The Journal of Physiology

Given recent declines in North Pacific humpback whale (Megaptera novaeangliae) reproductive output and calf survival, there is additional urgency to better understand how mother–calf pairs allocate energy resources across their migratory cycle. Here, unoccupied aerial system (UAS; or drone) photogrammetry was used to quantify the body size and condition (BC) of humpback whales on their Hawaiʻi (HI) breeding and Southeast Alaska (SEAK) feeding grounds. Between 2018 and 2022, we collected 2410 measurements of 1659 individuals. Rates of change in body volume (BV) and length (BL) were quantified using 803 repeat measurements of 275 individuals. On average, HI mothers lost 0.106 m³ or 96.84 kg day⁻¹ while fasting, equivalent to 2641 MJ day⁻¹ or 830 kg of krill and 424 kg of Pacific herring daily. HI calf BV and BL increased by 0.035 m³ and 2.6 cm day⁻¹, respectively. In SEAK, maternal BV increased by 0.015 m³ or 14.54 kg day⁻¹ (367 MJ day⁻¹), while calf BV and BL increased by 0.039 m³ and 0.93 cm day⁻¹, respectively. Maternal investment in calf growth correlated with both female BL and BC, with larger females producing larger, faster‐growing calves. Finally, using 330 measurements from 156 females, we quantified differences in BC increase over four feeding seasons. Lactating females exhibited an average BC increase of 6.10%, half that of unclassified females (13.51%) and six times lower than pregnant females (37%). These findings represent novel insights into the life history of humpback whales across their migratory cycle, providing key baseline data for bioenergetic models elucidating the effects of anthropogenic disturbance and rapidly changing ocean ecosystems. image Key points On average, Hawaiʻi (HI) mothers lost 0.106 m³ or 96.84 kg day⁻¹, equivalent to 2641 MJ day⁻¹. Over a 60 day period, this corresponded to an estimated mean energetic cost of 158 GJ, or ≈50 tons of krill or ≈25 tons of Pacific herring, surpassing the total energetic cost of gestation estimated for humpback whales of similar length. In Southeast Alaska (SEAK), maternal body volume (BV) increased by just 0.015 m³ or 14.54 kg day⁻¹ (367 MJ day⁻¹). Further, SEAK lactating females showed the slowest rates of growth in body width and condition over a 150 day period compared to non‐lactating females. Maternal investment in calf growth correlated with both maternal length and body condition, with larger females producing larger, faster‐growing calves. In HI, however, the ratio between maternal BV lost and calf BV gained (conversion efficiency) was relatively low compared to other mammals.

Improving our understanding of energy allocation in reproduction is key for accurately parameterizing bioenergetic models to assess population responses to environmental perturbations and anthropogenic disturbance. We quantified the energetic cost of gestation in humpback whales (Megaptera novaeangliae) using historical whaling records, non‐invasive unoccupied aerial system (UAS) photogrammetry and post mortem tissue samples. First, we estimated relative birth size using body length measurements of 678 mother–fetus pairs from historical whaling records and 987 mother–calf pairs measured in situ using UAS‐photogrammetry. The total energetic cost of gestation includes fetal growth (FG), heat increment of gestation and placental tissue development. FG was modelled from conception to birth, with fetal volume and mass estimated using the volume‐to‐length relationship of perinatal calves and published humpback whale tissue composition estimates. Tissue‐specific energy content was quantified using post mortem bone, muscle, viscera and blubber samples from a neonatal humpback whale. Placental tissue development was estimated using humpback whale placental tissue and published equations. Relative birth length was found to be 33.75% (95% CI: 32.10–34.61) of maternal length. FG rates and absolute birth size increased with maternal length, with exponential growth in fetal length, volume and mass resulting in minimal energetic costs over the first two quadmesters (0.01–1.08%) before increasing significantly in the final quadmester (98.92%). Gestational heat constituted the greatest energetic cost (90.42–94.95%), followed by fetal (4.58–7.76%) and placental (0.37–1.83%) tissue growth. Our findings highlight the energetic costs endured by capital breeding females preceding parturition, with the most substantial energetic costs of gestation coinciding with migration and fasting. image Key points We quantified the energetic cost of gestation using body length measurements of mother–fetus pairs from historical whaling records, length estimates of mother–calf pairs measured in situ using aerial photogrammetry and post mortem tissue samples. Fetal growth rates and birth size increased with maternal length, with fetal length, volume and mass increasing exponentially over gestation. Energetic costs over the first two quadmesters were negligible (0.01–1.08%) before increasing significantly in the final quadmester (98.92%). Though larger females incur nearly twice the energetic cost of smaller females, they are likely buffered by greater absolute energy reserves, suggesting smaller females may be less resilient to perturbations in energy balance. We demonstrate the significant energetic costs incurred by pregnant humpback whales, with most of the energetic expenditure occurring over the final 100 days of gestation. Late‐pregnant females are, therefore, particularly vulnerable to disruptions in energy balance, given periods of greatest energetic stress coincide with fasting and migration.

Preeclampsia (PE) is a hypertensive disorder during human pregnancy. Aryl hydrocarbon receptor (AhR) is a ligand‐activated transcription factor. Exogenous and endogenous AhR ligands can induce hypertension in male rats and mice. Herein, using rats as a model, we tested the hypothesis that over‐regulation of endogenous AhR ligands during pregnancy impairs vascular functions by disrupting the transcriptome in the placenta, contributing to the development of PE. Pregnant rats were injected daily with an endogenous AhR ligand, 2‐(1′H‐indole‐3′‐carbonyl)‐thiazole‐4‐carboxylic acid methyl ester (ITE), from gestational day (GD) 10 to 19. Maternal mean blood pressure was measured on GD16–20. Proteinuria and uteroplacental blood flow were monitored on GD20. Placentas collected on GD20 were used to determine changes in vascular density and transcriptome. Compared with the vehicle control, ITE elevated maternal mean blood pressure by 22% and 16% on GD16 and 17, respectively. ITE increased proteinuria by 50% and decreased uteroplacental blood flow by 26%. ITE reduced the placental vascular density by 18%. RNA sequencing analysis revealed that ITE induced 1316 and 2020 differentially expressed genes (DEGs) in female and male placentas, respectively. These DEGs were enriched in pathways relevant to heart diseases, vascular functions and inflammation. Bioinformatics analysis also predicted that ITE altered immune cell infiltration in placentas depending on fetal sex. These data suggest that over‐regulation of endogenous AhR ligands may lead to PE with impaired vascular functions and disrupted fetal sex‐specific transcriptomes and immune cell infiltration in placentas. These AhR ligand‐induced DEGs and pathways may represent promising therapeutic targets for PE‐induced cardiovascular dysfunctions. image Key points An endogenous AhR ligand (ITE) elevated maternal blood pressure and proteinuria in pregnant rats, and decreased uteroplacental blood flow and fetal and placental growth, all of which are hallmarks of preeclampsia. ITE reduced vascular density and altered immune cell distribution in rat placentas. ITE dysregulated transcriptomes in rat placentas in a fetal sex‐specific manner. These ITE‐dysregulated genes and pathways are highly relevant to diseases of heart, vascular functions and inflammatory responses.

Gut hormones control intestinal function, metabolism and appetite, and have been harnessed therapeutically to treat type 2 diabetes and obesity. Our understanding of the enteroendocrine axis arises largely from animal studies, but intestinal organoid models make it possible to identify, genetically modify and purify human enteroendocrine cells (EECs). This study aimed to map human EECs using single‐cell RNA sequencing. Organoids derived from human duodenum and ileum were genetically modified using CRISPR‐Cas9 to express the fluorescent protein Venus driven by the chromogranin‐A promoter. Fluorescent cells from CHGA‐Venus organoids were purified by flow cytometry and analysed by 10X single‐cell RNA sequencing. Cluster analysis separated EEC populations, allowing an examination of differentially expressed hormones, nutrient‐sensing machinery, transcription factors and exocytotic machinery. Bile acid receptor GPBAR1 was most highly expressed in L‐cells (producing glucagon‐like peptide 1 and peptide YY), long‐chain fatty acid receptor FFAR1 was highest in I‐cells (cholecystokinin), K‐cells (glucose‐dependent insulinotropic polypeptide) and L‐cells, short‐chain fatty acid receptor FFAR2 was highest in ileal L‐cells and enterochromaffin cells, olfactory receptor OR51E1 was notably expressed in ileal enterochromaffin cells, and the glucose‐sensing sodium glucose cotransporter SLC5A1 was highly and differentially expressed in K‐ and L‐cells, reflecting their known responsiveness to ingested glucose. The organoid EEC atlas was merged with published data from human intestine and organoids, with good overlap between enteroendocrine datasets. Understanding the similarities and differences between human EEC types will facilitate the development of drugs targeting the enteroendocrine axis for the treatment of conditions such as diabetes, obesity and intestinal disorders. image Key points Gut hormones regulate intestinal function, nutrient homeostasis and metabolism and form the basis of the new classes of drugs for obesity and diabetes. As enteroendocrine cells (EECs) comprise only ∼1% of the intestinal epithelium, they are under‐represented in current single‐cell atlases. To identify, compare and characterise human EECs we generated chromogranin‐A labelled organoids from duodenal and ileal biopsies by CRISPR‐Cas9. Fluorescent chromogranin‐A positive EECs were purified and analysed by single‐cell RNA sequencing, revealing predominant cell clusters producing different gut hormones. Cell clusters exhibited differential expression of nutrient‐sensing machinery including bile acid receptors, long‐ and short‐chain fatty acid receptors and glucose transporters. Organoid‐derived EECs mapped well onto data from native intestinal cell populations, extending coverage of EECs.

Cardiometabolic syndromes including diabetes and obesity are associated with occurrence of heart failure with diastolic dysfunction. There are no specific treatments for diastolic dysfunction, and therapies to manage symptoms have limited efficacy. Understanding of the cardiomyocyte origins of diastolic dysfunction is an important priority to identify new therapeutics. The investigative goal was to experimentally define in vitro stiffness properties of isolated cardiomyocytes derived from rodent hearts exhibiting diastolic dysfunction in vivo in response to dietary induction of cardiometabolic disease. Male mice fed a high fat/sugar diet (HFSD vs. control) exhibited diastolic dysfunction (echo E/e′ Doppler ratio). Intact paced cardiomyocytes were functionally investigated in three conditions: non‐loaded, loaded and stretched. Mean stiffness of HFSD cardiomyocytes was 70% higher than control. E/e′ for the HFSD hearts was elevated by 35%. A significant relationship was identified between in vitro cardiomyocyte stiffness and in vivo dysfunction severity. With conversion from the non‐loaded to loaded condition, the decrement in maximal sarcomere lengthening rate was more accentuated in HFSD cardiomyocytes (vs. control). With stretch, the Ca²⁺ transient decay time course was prolonged. With increased pacing, cardiomyocyte stiffness was elevated, yet diastolic Ca²⁺ elevation was attenuated. Our findings show unequivocally that cardiomyocyte mechanical dysfunction cannot be detected by analysis of non‐loaded shortening. Collectively, these findings demonstrate that a component of cardiac diastolic dysfunction in cardiometabolic disease is derived from cardiomyocyte stiffness. Differential responses to load, stretch and pacing suggest that a previously undescribed alteration in myofilament–Ca²⁺ interaction contributes to intrinsic cardiomyocyte stiffness in cardiometabolic disease. image Key points Understanding cardiomyocyte stiffness components is an important priority for identifying new therapeutics for diastolic dysfunction, a key feature of cardiometabolic disease. In this study cardiac function was measured in vivo (echocardiography) for mice fed a high‐fat/sugar diet (HFSD, ≥25 weeks). Performance of intact isolated cardiomyocytes derived from the same hearts was measured during pacing under non‐loaded, loaded and stretched conditions in vitro. Calibrated cardiomyocyte stretches demonstrated that stiffness (stress/strain) was elevated in HFSD cardiomyocytes in vitro and correlated with diastolic dysfunction (E/e′) in vivo. HFSD cardiomyocyte Ca²⁺ transient decay was prolonged in response to stretch. Stiffness was accentuated with pacing increase while the elevation in diastolic Ca²⁺ was attenuated. Data show unequivocally that cardiomyocyte mechanical dysfunction cannot be detected by analysis of non‐loaded shortening. These findings suggest that stretch‐dependent augmentation of the myofilament–Ca²⁺ response during diastole partially underlies elevated cardiomyocyte stiffness and diastolic dysfunction of hearts of animals with cardiometabolic disease.

It has been hypothesised that skeletal muscle protein turnover is affected by menstrual cycle phase with a more anabolic environment during the follicular vs. the luteal phase. We assessed the influence of menstrual cycle phase on muscle protein synthesis and myofibrillar protein breakdown in response to 6 days of controlled resistance exercise in young females during peak oestrogen and peak progesterone, using stable isotopes, unbiased metabolomics and muscle biopsies. We used comprehensive menstrual cycle phase‐detection methods, including cycle tracking, blood samples and urinary test kits, to classify menstrual phases. Participants (n = 12) completed two 6 day study phases in a randomised order: late follicular phase and mid‐luteal phase. Participants performed unilateral resistance exercise in each menstrual cycle phase, exercising the contralateral leg in each phase in a counterbalanced manner. Follicular phase myofibrillar protein synthesis (MPS) rates were 1.33 ± 0.27% h⁻¹ in the control leg and 1.52 ± 0.27% h⁻¹ in the exercise leg. Luteal phase MPS was 1.28 ± 0.27% h⁻¹ in the control leg and 1.46 ± 0.25% h⁻¹ in the exercise leg. We observed a significant effect of exercise (P < 0.001) but no effect of cycle phase or interaction. There was no significant effect of menstrual cycle phase on whole‐body myofibrillar protein breakdown (P = 0.24). Using unbiased metabolomics, we observed no notable phase‐specific changes in circulating blood metabolites associated with any particular menstrual cycle phase. Fluctuations in endogenous ovarian hormones influenced neither MPS, nor MPB in response to resistance exercise. Skeletal muscle is not more anabolically responsive to resistance exercise in a particular menstrual cycle phase. image Key points It has been hypothesised that the follicular (peak oestrogen) vs. the luteal (peak progesterone) phase of the menstrual cycle is more advantageous for skeletal muscle anabolism in response to resistance exercise. Using best practice methods to assess menstrual cycle status, we measured integrated (over 6 days) muscle protein synthesis (MPS) and myofibrillar protein breakdown (MPB) following resistance exercise in females (n = 12) in their follicular and luteal phases. We observed the expected differences in oestrogen and progesterone concentrations that confirmed our participants’ menstrual cycle phase; however, there were no notable metabolic pathway differences, as measured using metabolomics, between cycle phases. We observed that resistance exercise stimulated MPS, but there was no effect of menstrual cycle phase on either resting or exercise‐stimulated MPS or MPB. Our data show no greater anabolic effect of resistance exercise in the follicular vs. the luteal phase of the menstrual cycle.

Kv4 channels generate A‐type current known to regulate neuronal excitability. Its role in processing timing information is understudied, especially in the auditory system where temporal information is crucial for hearing. In the cochlear nucleus, principal bushy neurons are specialized for temporal processing with distinct biophysical properties owing to their expression of various voltage‐gated ion channels. Previous studies reported conflicting information regarding the expression and potential role of Kv4 channels in these neurons. We explored these questions using electrophysiology in CBA/CaJ mice of either sex. A‐type current was isolated from 88% of bushy neurons using Kv4 channel‐selective blocker Jingzhaotoxin‐X (JZ‐X), which increased the intrinsic excitability of bushy neurons without altering their synaptic input. During high‐rate activity, JZ‐X treatment significantly increased the spike jitter and reduced the firing threshold of bushy neurons. In old mice, A‐type current in bushy neurons reduced in magnitude but maintained current density, accompanied by decreased membrane surface area. In contrast, TEA‐sensitive Kv3 current reduced in both magnitude and current density, indicative of a greater contribution to the altered biophysical properties of bushy neurons during ageing. Our findings suggest that Kv4 channels play significant roles in regulating neuronal excitability and improving the temporal processing of bushy neurons. Such function is likely retained with age and is not the primary mechanism driving compromised temporal processing under age‐related hearing loss. image Key points Most bushy neurons of the cochlear nucleus exhibit Kv4‐mediated A‐type current. A‐type current regulates neuronal excitability of bushy neurons without contributing to the synaptic transmission at the endbulb of Held. A‐type current increases the firing threshold and improves the temporal precision of spikes in bushy neurons during high‐rate activity. A‐type current reduces peak amplitude in bushy neurons during ageing but maintains current density. Decreased Kv3 current, rather than Kv4 current, likely play more significant roles in altering the biophysical properties of bushy neurons during ageing, contributing to compromised temporal processing during age‐related hearing loss.

A fundamental question in sensory neuroscience revolves around how neurons represent complex visual stimuli. In mammalian primary visual cortex (V1), neurons decode intricate visual features to identify objects, with most being selective for edge orientation, but with half of those also developing invariance to edge position within their receptive fields. Position invariance allows cells to continue to code an edge even when it moves around. Combining feature selectivity and invariance is integral to successful object recognition. Considering the marsupial–eutherian divergence 160 million years ago, we explored whether feature selectivity and invariance was similar in marsupials and eutherians. We recovered the spatial filters and non‐linear processing characteristics of the receptive fields of neurons in wallaby V1 and compared them with previous results from cat cortex. We stimulated the neurons in V1 with white Gaussian noise and analysed responses using the non‐linear input model. Wallabies exhibit the same high percentage of orientation selective neurons as cats. However, in wallabies we observed a notably higher prevalence of neurons with three or more filters compared to cats. We show that having three or more filters substantially increases phase invariance in the V1s of both species, but that wallaby V1 accentuates this feature, suggesting that the species condenses more processing into the earliest cortical stage. These findings suggest that evolution has led to more than one solution to the problem of creating complex visual processing strategies. image Key points Previous studies have shown that the primary visual cortex (V1) in mammals is essential for processing complex visual stimuli, with neurons displaying selectivity for edge orientation and position. This research explores whether the visual processing mechanisms in marsupials, such as wallabies, are similar to those in eutherian mammals (e.g. cats). The study found that wallabies have a higher prevalence of neurons with multiple spatial filters in V1, indicating more complex visual processing. Using a non‐linear input model, we demonstrated that neurons with three or more filters increase phase invariance. These findings suggest that marsupials and eutherian mammals have evolved similar strategies for visual processing, but marsupials have condensed more capacity to build phase invariance into the first step in the cortical pathway.

Pulmonary hypertension (PH) is a chronic, progressive disease characterized by pulmonary vascular remodelling, dyspnoea and exercise intolerance. Key facets of dyspnoea and exercise intolerance include skeletal and respiratory muscle contractile and metabolic disturbances; however, muscle perfusion during exercise has not been investigated. We hypothesized that diaphragm blood flow (Q̇$\dot{Q}$) would be increased and locomotory muscle Q̇$\dot{Q}$ would be decreased during submaximal treadmill running in PH rats compared to healthy controls. Female Sprague–Dawley rats were injected (i.p.) with monocrotaline to induce PH (n = 16), or a vehicle control (n = 15). Disease progression was monitored via echocardiography. When moderate disease severity was confirmed, maximal oxygen uptake (V̇O2max${{\dot{V}}_{{{{\mathrm{O}}}_{{{2}^{{\mathrm{max}}}}}}}}$) tests were performed. Rats were given >24 h to recover, and then fluorescent microspheres were infused during treadmill running (20 m/min, 10% grade; ∼40–50% maximal speed attained during the V̇O2max${{\dot{V}}_{{{{\mathrm{O}}}_{{{2}^{{\mathrm{max}}}}}}}}$ test) to determine tissue Q̇$\dot{Q}$. In PH rats compared with healthy controls, V̇O2max${{\dot{V}}_{{{{\mathrm{O}}}_{{{2}^{{\mathrm{max}}}}}}}}$ was lower (84 (7) vs. 67 (11) ml/min/kg; P < 0.001), exercising diaphragm Q̇$\dot{Q}$ was 35% higher and soleus Q̇$\dot{Q}$ was 28% lower. Diaphragm Q̇$\dot{Q}$ was negatively correlated with soleus Q̇$\dot{Q}$ and V̇O2max${{\dot{V}}_{{{{\mathrm{O}}}_{{{2}^{{\mathrm{max}}}}}}}}$ in PH rats. Furthermore, there was regional Q̇$\dot{Q}$ redistribution in the diaphragm in PH compared to healthy rats, which may represent or underlie diaphragmatic weakness in PH. These findings suggest the presence of a pathological respiratory muscle blood flow steal phenomenon in PH and that this may contribute to the exercise intolerance reported in patients. image Key points Pulmonary hypertension (PH) impairs exercise tolerance, which is associated with skeletal and respiratory muscle dysfunction. Increased work of breathing in PH may augment diaphragm blood flow and lower locomotory muscle blood flow during exercise, hindering exercise tolerance. Our findings demonstrate that respiratory muscle blood flow is increased while the locomotory muscle is decreased in PH compared to healthy rats during exercise, suggesting that blood flow is preferentially redistributed to sustain ventilatory demand. Furthermore, blood flow is regionally redistributed within the diaphragm in PH, which may underlie diaphragm dysfunction. Greater respiratory muscle work at a given workload in PH commands higher respiratory muscle blood flow, impairing locomotory muscle oxygen delivery and compromising exercise tolerance, which may be improved by therapeutics which target the diaphragm vasculature.

GABA is the primary inhibitory neurotransmitter. Membrane currents evoked by GABAA receptor activation have uniquely small driving forces: their reversal potential (EGABA) is very close to the resting membrane potential. As a consequence, GABAA currents can flow in either direction, depending on both the membrane potential and the local intra and extracellular concentrations of the primary permeant ion, chloride (Cl). Local cytoplasmic Cl concentrations vary widely because of displacement of mobile Cl ions by relatively immobile anions. Here, we use new reporters of extracellular chloride (Cl⁻o) to demonstrate that Cl is displaced in the extracellular space by high and spatially heterogenous concentrations of immobile anions including sulfated glycosaminoglycans (sGAGs). Cl⁻o varies widely, and the mean Cl⁻o is only half the canonical concentration (i.e. the Cl concentration in the cerebrospinal fluid). These unexpectedly low and heterogenous Cl⁻o domains provide a mechanism to link the varied but highly stable distribution of sGAGs and other immobile anions in the brain's extracellular space to neuronal signal processing via the effects on the amplitude and direction of GABAA transmembrane Cl currents. image Key points Extracellular chloride concentrations in the brain were measured using a new chloride‐sensitive organic fluorophore and two‐photon fluorescence lifetime imaging. In vivo, the extracellular chloride concentration was spatially heterogenous and only half of the cerebrospinal fluid chloride concentration Stable displacement of extracellular chloride by immobile extracellular anions was responsible for the low extracellular chloride concentration The changes in extracellular chloride were of sufficient magnitude to alter the conductance and reversal potential of GABAA chloride currents The stability of the extracellular matrix, the impact of the component immobile anions, including sulfated glycosaminoglycans on extracellular chloride concentrations, and the consequent effect on GABAA signalling suggests a previously unappreciated mechanism for modulating GABAA signalling.

The pituitary gland produces and secretes a variety of hormones that are essential to life, such as for the regulation of growth and development, metabolism, reproduction, and the stress response. This is achieved through an intricate signalling interplay between the brain and peripheral feedback signals that shape pituitary cell excitability by regulating the ion channel properties of these cells. In addition, endocrine anterior pituitary cells spontaneously fire action potentials to regulate the intracellular calcium ([Ca²⁺]i) level, an essential signalling conduit for hormonal secretion. To this end, pituitary cells must regulate their resting membrane potential (RMP) close to the firing threshold, but the molecular identity of the ionic mechanisms responsible for this remains largely unknown. Here, we revealed that the sodium leak channel NALCN, known to modulate neuronal excitability elsewhere in the brain, regulates excitability in the mouse anterior endocrine pituitary cells. Using viral transduction combined with powerful electrophysiology methods and calcium imaging, we show that NALCN forms the major Na⁺ leak conductance in these cells, appropriately tuning cellular RMP for sustaining spontaneous firing activity. Genetic depletion of NALCN channel activity drastically hyperpolarised these cells, suppressing their firing and [Ca²⁺]i oscillations. Remarkably, despite this profound function of NALCN conductance in controlling pituitary cell excitability, it represents a very small fraction of the total cell conductance. Because NALCN responds to hypothalamic hormones, our results also provide a plausible mechanism through which hormonal feedback signals from the brain and body could powerfully affect pituitary activity to influence hormonal function. image Key points Pituitary hormones are essential to life as they regulate important physiological processes, such as growth and development, metabolism, reproduction and the stress response. Pituitary hormonal secretion relies on the spontaneous electrical activity of pituitary cells and co‐ordinated inputs from the brain and periphery. This appropriately regulates intracellular calcium signals in pituitary cells to trigger hormonal release. Using viral transduction in combination with electrophysiology and calcium imaging, we show that the activity of the background leak channel NALCN is a major controlling factor in eliciting spontaneous electrical activity and intracellular calcium signalling in pituitary cells. Remarkably, our results revealed that a minute change in NALCN activity could have a major influence on pituitary cell excitability. Our study provides a plausible mechanism through which the brain and body could intricately control pituitary activity to influence hormonal function.

The striking increase of uterine blood flow during pregnancy is essential for normal fetal development as well as for cardiovascular well‐being of the mother. Yet, the underlying mechanisms of pregnancy‐mediated vasodilatation of the uterine artery are not fully understood. In this study, we test the hypothesis that Rad, a monomeric G protein, is a novel regulatory mechanism in inhibiting CaV1.2 channel currents in uterine artery haemodynamic adaptation to pregnancy in a sheep model. We found that pregnancy significantly upregulates Rad expression and decreases CaV1.2 channel currents in uterine arterial smooth muscle cells. Rad knockdown ex vivo and in vivo increases CaV1.2 activity and channel window currents by reducing steady‐state inactivation in uterine arteries of pregnant sheep, recapitulating the phenotype of uterine arteries in non‐pregnant animals. Moreover, Rad knockdown in vivo in pregnant sheep enhances myogenic tone and phenylephrine‐induced vasoconstriction of uterine arteries. Whereas knockdown of Rad has no effect on mesenteric arterial CaV1.2 channel activity and mean arterial blood pressure, it significantly increases uterine vascular resistance and decreases uterine artery blood flow. Our study reveals a novel cause‐and‐effect mechanism of Rad in pregnancy‐induced suppression of CaV1.2 channel activity in uterine arteries to facilitate increased uterine blood flow, providing new insights into fundamental mechanisms of uterine haemodynamic adaptation to pregnancy. image Key points Pregnancy suppresses CaV1.2 channel currents in uterine arterial smooth muscle cells. Rad, a monomeric G protein, is upregulated in uterine arteries of pregnant sheep. Rad knockdown ex vivo or in vivo increases CaV1.2 channel currents in uterine arteries from pregnant ewes. In vivo knockdown of Rad elevates uterine vascular resistance and decreases uterine blood flow in pregnant sheep. The study reveals a novel mechanism of Rad in pregnancy‐induced suppression of CaV1.2 channel activity in uterine arterial haemodynamic adaptation to pregnancy.

In recent years, the ageing population has increasingly grown. This process carries a range of pathophysiological changes involving alterations in the skeletal muscle, vascular endothelium and brain function, becoming an important risk factor for developing cognitive disorders and cardiovascular diseases. With ageing, there is a decrease in muscle mass and muscle strength, and a relationship between muscle strength decrease and cognitive decline has been shown. Lower handgrip strength has been linked to memory impairment, lower global cognitive function, decreased attention and reduced visuospatial abilities in the elderly, but understanding of the underlying mechanisms that explain the link between altered skeletal muscle function and structure, endothelial dysfunction, and the role of endothelial dysfunction in the onset of cognitive disorders has been scarcely explored. This review aims to detail the cellular and molecular mechanisms by which the progressive changes associated with ageing can alter healthy skeletal muscle and endothelial function, creating an environment of oxidative stress, inflammation and mitochondrial dysfunction. These changes can lead to reduced muscle strength, and the secretion of detrimental endothelial factors, resulting in endothelial dysfunction, blood–brain barrier disruption, and damage to neurons and microglia, ultimately accelerating the onset of cognitive disorders in the elderly. In addition, we aimed to describe the mechanisms that potentially explain how preserving muscular function with resistance training could prevent brain function deterioration, including the production of different factors that allow an improved endothelial function, haemodynamic parameters and brain plasticity, ultimately delaying the onset of cognitive impairment and chronic diseases. image

The standard conception of cardiac conduction is based on the cable theory of nerve conduction, which treats cardiac tissue as a continuous syncytium described by the Hodgkin–Huxley equations. However, cardiac tissue is composed of discretized cells with microscopic and macroscopic heterogeneities and discontinuities, such as subcellular localizations of sodium channels and connexins. In addition to this, there are heterogeneities in the distribution of sympathetic and parasympathetic nerves, which powerfully regulate impulse propagation. In the continuous models, the ultrastructural details, i.e. the microscopic heterogeneities and discontinuities, are ignored by ‘coarse graining’ or ‘smoothing’. However, these ultrastructural components may play crucial roles in cardiac conduction and arrhythmogenesis, particularly in disease states. We discuss the current progress of modelling the effects of ultrastructural components on electrical conduction, the issues and challenges faced by the cardiac modelling community, and how to scale up conduction properties at the subcellular (microscopic) scale to the tissue and whole‐heart (macroscopic) scale in future modelling and experimental studies, i.e. how to link the ultrastructure at different scales to impulse conduction and arrhythmogenesis in the heart. image

The Drosophila neuromuscular junction (NMJ) is a powerful genetic system that has revealed numerous conserved mechanisms for synapse development and homeostasis. The fly NMJ uses glutamate as the excitatory neurotransmitter and relies on kainate‐type glutamate receptors and their auxiliary protein Neto for synapse assembly and function. However, despite decades of study, the reconstitution of NMJ glutamate receptors using heterologous systems has been achieved only recently, and there are no reports on the gating properties for the recombinant receptors. Here, using outside‐out, patch clamp recordings and fast ligand application, we examine for the first time the biophysical properties of native type‐A and type‐B NMJ receptors in complexes with either Neto‐α or Neto‐β and compare them with recombinant receptors expressed in HEK293T cells. We found that type‐A and type‐B receptors have strikingly different gating properties that are further modulated by Neto‐α and Neto‐β. We captured single‐channel events and revealed major differences between type‐A and type‐B receptors and also between Neto splice variants. Surprisingly, we found that deactivation is extremely fast and that the decay of synaptic currents resembles the rate of ionotropic glutamate receptor (iGluR) desensitization. The functional analyses of recombinant iGluRs that we report here should greatly facilitate the interpretation of compound in vivo phenotypes of mutant animals. image Key points We report the reconstitution of Drosophila neuromuscular junction ionotropic glutamate receptors (iGluRs) with Neto splice forms. Using outside‐out patches and fast ligand application, we examine the deactivation and desensitization of the four iGluR/Neto complexes found in vivo. Expression of functional channels is absolutely dependent on Neto. Single‐channel recordings revealed different lifetimes for different receptor complexes. The decay of synaptic currents is controlled by desensitization.

Through the modulation of its surround, an identical visual stimulus can be perceived as more or less salient, allowing it to either stand out or seamlessly integrate with the rest of the visual scene. Gamma rhythms are associated with processing stimulus features across extensive areas of the visual field. Consistent with this concept, the magnitude of visually induced gamma rhythm depends on how well stimulus features aligned both within and outside the classical receptive field (CRF) at the recording site. However, there still exists some uncertainty regarding the encoding of context‐modulated orientation discontinuity by gamma rhythms. To address this concern, we conducted extracellular recordings in layers II/III and IV of area V1 using lightly anaesthetized mice to investigate the gamma tuning for stimuli with orientation discontinuity. Our study revealed that gamma rhythms exhibit a preference for stimuli with orientation discontinuity similar to the spiking responses observed in V1, which contradicts the findings of previous studies. Furthermore, the gamma tuning of discontinuous orientations exhibits a moderate correlation with spike tuning and a positive correlation with the strength of surround suppression. Therefore, our study suggests a close association between gamma tuning and nearby spiking tuning; additionally, it highlights the connection between the encoding of visual features by gamma rhythms and functional architecture, as well as neural signal integration. image Key points Visual context modulates the gamma rhythms in the primary visual cortex. Discontinuous orientation elicits significantly enhanced gamma rhythms compared to the iso‐orientation stimulus. The gamma tuning of discontinuous orientations exhibits a moderate correlation with spike tuning. Gamma tuning of orientation discontinuity exhibits a positive correlation with the strength of surround suppression.

We investigated acute effects of the Na⁺,K⁺‐ATPase (NKA) inhibitor, digoxin, on muscle NKA content and isoforms, arterial plasma [K⁺] ([K⁺]a) and fatigue with intense exercise. In a randomised, crossover, double‐blind design, 10 healthy adults ingested 0.50 mg digoxin (DIG) or placebo (CON) 60 min before cycling for 1 min at 60% V̇O2peak${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{peak}}}}$ then at 95% V̇O2peak${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{peak}}}}$ until fatigue. Pre‐ and post‐exercise muscle biopsies were analysed for [³H]‐ouabain binding site content without (OB‐Fab) and after incubation in digoxin antibody (OB+Fab) and NKA α1‐2 and β1‐2 isoform proteins. In DIG, pre‐exercise serum [digoxin] reached 3.36 (0.80) nM [mean (SD)] and muscle NKA–digoxin occupancy was 8.2%. Muscle OB‐Fab did not differ between trials, whereas OB+Fab was higher in DIG than CON (8.1%, treatment main effect, P = 0.001), whilst muscle NKA α1‐2 and β1‐2 abundances were unchanged by digoxin. Fatigue occurred earlier in DIG than CON [−7.7%, 2.90 (0.77) vs. 3.14 (0.86) min, respectively; P = 0.037]. [K⁺]a increased during exercise until 1 min post‐exercise (P = 0.001), and fell below baseline at 3–10 (P = 0.001) and 20 min post‐exercise (P = 0.022, time main effect). In DIG, [K⁺]a (P = 0.035, treatment effect) and [K⁺]a rise pre‐fatigue were greater [1.64 (0.73) vs. 1.55 (0.73), P = 0.016], with lesser post‐exercise [K⁺]a decline than CON [−2.55 (0.71) vs. −2.74 (0.62) mM, respectively, P = 0.003]. Preserved muscle OB‐Fab with digoxin, yet increased OB+Fab with unchanged NKA isoforms, suggests a rapid regulatory assembly of existing NKA α and β subunits exists to preserve muscle NKA capacity. Nonetheless, functional protection against digoxin was incomplete, with earlier fatigue and perturbed [K⁺]a with exercise. image Key points Intense exercise causes marked potassium (K⁺) shifts out of contracting muscle cells, which may contribute to muscle fatigue. Muscle and systemic K⁺ perturbations with exercise are largely regulated by increased activity of Na⁺,K⁺‐ATPase in muscle, which can be specifically inhibited by the cardiac glycoside, digoxin. We found that acute oral digoxin in healthy adults reduced time to fatigue during intense exercise, elevated the rise in arterial plasma K⁺ concentration during exercise and slowed K⁺ concentration decline post‐exercise. Muscle functional Na⁺,K⁺‐ATPase content was not reduced by acute digoxin, despite an 8.2% digoxin occupancy, and was unchanged at fatigue. Muscle Na⁺,K⁺‐ATPase isoform protein abundances were unchanged by digoxin or fatigue. These suggest possible rapid assembly of existing subunits into functional pumps. Thus, acute digoxin impaired performance and exacerbated plasma K⁺ disturbances with intense, fatiguing exercise in healthy participants. These occurred despite the preservation of functional Na⁺,K⁺‐ATPase in muscle.