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VU0546110 Inhibits SLO3-γ2 Channels in HEK293 Cells. (A) Chemical structure of VU0546110. (B) Diagram of whole-cell patch-clamp configuration and intra-and extracellular ionic compositions. (C) Representative recordings of whole-cell currents at indicated VU0546110 concentrations. Currents at +100 mV are highlighted in red. (D) Representative trace of SLO3-γ2 currents in the presence and absence of 10 µM quinidine. Quinidine-sensitive currents were derived by subtracting currents in the presence of quinidine from control currents. (E) Currents at +100 mV were normalized to the current with no VU0546110 (1) and 10 µM quinidine (0) and fit with a modified Hill equation to derive the IC50.
Source publication
To fertilize an oocyte, the membrane potential of both mouse and human sperm must hyperpolarize (become more negative inside). Determining the molecular mechanisms underlying this hyperpolarization is vital for developing new contraceptive methods and detecting causes of idiopathic male infertility. In mouse sperm, hyperpolarization is caused by ac...
Contexts in source publication
Context 1
... Based on its initial potency for SLO3 inhibition, one of the most promising compounds identified in the high-throughput screen was VU0546110 ( Fig. 2A). To confirm the ability of this compound to inhibit SLO3, we performed whole-cell patch-clamp experiments on HEK293 cells that stably expressed human SLO3 channels and the γ2 accessory subunit (Fig. 2B). The human SLO3 current was almost completely inhibited at 10 µM VU0546110 (Fig. 2C). To eliminate possible effects of VU0546110 on ...
Context 2
... Based on its initial potency for SLO3 inhibition, one of the most promising compounds identified in the high-throughput screen was VU0546110 ( Fig. 2A). To confirm the ability of this compound to inhibit SLO3, we performed whole-cell patch-clamp experiments on HEK293 cells that stably expressed human SLO3 channels and the γ2 accessory subunit (Fig. 2B). The human SLO3 current was almost completely inhibited at 10 µM VU0546110 (Fig. 2C). To eliminate possible effects of VU0546110 on currents from channels endogenously expressed in HEK293 cells, we treated the cells with the non-selective K + channel inhibitor quinidine (19). For each concentration of VU0546110 tested, we subtracted ...
Context 3
... identified in the high-throughput screen was VU0546110 ( Fig. 2A). To confirm the ability of this compound to inhibit SLO3, we performed whole-cell patch-clamp experiments on HEK293 cells that stably expressed human SLO3 channels and the γ2 accessory subunit (Fig. 2B). The human SLO3 current was almost completely inhibited at 10 µM VU0546110 (Fig. 2C). To eliminate possible effects of VU0546110 on currents from channels endogenously expressed in HEK293 cells, we treated the cells with the non-selective K + channel inhibitor quinidine (19). For each concentration of VU0546110 tested, we subtracted the currents that remained in the presence of 10 µM quinidine (Fig. 2D). We then ...
Context 4
... at 10 µM VU0546110 (Fig. 2C). To eliminate possible effects of VU0546110 on currents from channels endogenously expressed in HEK293 cells, we treated the cells with the non-selective K + channel inhibitor quinidine (19). For each concentration of VU0546110 tested, we subtracted the currents that remained in the presence of 10 µM quinidine (Fig. 2D). We then measured the steady-state current evoked at +100 mV potential, normalized the values to those obtained in the absence of VU0546110, and generated a doseresponse curve, which we fitted with the Hill Equation (Fig. 2E). We determined that VU0546110 inhibited SLO3 currents with an IC50 of 1.287 ± 0.1004 ...
Context 5
... For each concentration of VU0546110 tested, we subtracted the currents that remained in the presence of 10 µM quinidine (Fig. 2D). We then measured the steady-state current evoked at +100 mV potential, normalized the values to those obtained in the absence of VU0546110, and generated a doseresponse curve, which we fitted with the Hill Equation (Fig. 2E). We determined that VU0546110 inhibited SLO3 currents with an IC50 of 1.287 ± 0.1004 ...
Context 6
... they traverse through the male and female reproductive tracts, sperm experience environments with different pH. Thus, we wanted to determine whether the effects of VU0546110 depended on external pH. SI Appendix, Fig. S2A shows that VU0546110 was equally effective in inhibiting SLO3 at external pH 7. 2 To determine whether VU0546110 was selective for SLO3 over SLO1, we stably expressed SLO1 in HEK293 cells and measured the dose-response of SLO1 currents to VU0546110 (Fig. 3A). The IC50 for SLO1 was 59.80 ± 14.47 µM, more than 40-fold higher than the ...
Citations
... which is necessary for later capacitation events. However, several studies have demonstrated the importance of the K + channel Slo3 for capacitation/fertilization.89,90,255 Thus, this section reviews the literature regarding the physiological function of Slo3 in detail and proposes a hypothesis regarding the physiological role of Slo3 in capacitation/fertilization. ...
... As mentioned above, genetic and pharmacological approaches have been employed to elucidate the physiological functions of Slo3. Both Slo3 inhibition and genetic deletion of Slo3 inhibit overall capacitation-associated events (i.e., hyperpolarization of Em, hyperactivation, AR, and IVF).89,90,255 Further studies were conducted to elucidate the mechanism of Slo3 channel regulation of capacitation/fertilization and revealed the association between Slo3 and CatSper: Slo3 activation leads to the activation of the CatSper channel via hyperpolarization of Em to express hyperactivated motility.90,234,256 ...
... Both Slo3 inhibition and genetic deletion of Slo3 inhibit overall capacitation-associated events (i.e., hyperpolarization of Em, hyperactivation, AR, and IVF).89,90,255 Further studies were conducted to elucidate the mechanism of Slo3 channel regulation of capacitation/fertilization and revealed the association between Slo3 and CatSper: Slo3 activation leads to the activation of the CatSper channel via hyperpolarization of Em to express hyperactivated motility.90,234,256 Because CatSper plays a crucial role in capacitation, especially hyperactivation, this hypothesis seems likely.When the phenotypes of spermatozoa of Slo3 null mice were more closely compared with those of CatSper null mice, Slo3 null spermatozoa showed more severe defects than those of CatSper null spermatozoa; CatSper null spermatozoa exhibited normal AR and were able to fertilize ZP-free eggs45 whereas Slo3 null spermatozoa were unable to undergo AR and fertilize ZP-free eggs.89 ...
Background
Mammalian spermatozoa have to be “capacitated” to be fertilization‐competent. Capacitation is a collective term for the physiological and biochemical changes in spermatozoa that occur within the female body. However, the regulatory mechanisms underlying capacitation have not been fully elucidated.
Methods
Previously published papers on capacitation, especially from the perspective of ions/channels/transporters, were extracted and summarized.
Results
Capacitation can be divided into two processes: earlier events (membrane potential hyperpolarization, intracellular pH rise, intracellular Ca²⁺ rise, etc.) and two major later events: hyperactivation and the acrosome reaction. Earlier events are closely interconnected with each other. Various channels/transporters are involved in the regulation of them, which ultimately lead to the later events. Manipulating the extracellular K⁺ concentration based on the oviductal concentration modifies membrane potential; however, the later events and fertilization are not affected, suggesting the uninvolvement of membrane potential in capacitation. Hyperpolarization is a highly conserved phenomenon among mammalian species, indicating its importance in capacitation. Therefore, the physiological importance of hyperpolarization apart from membrane potential is suggested.
Conclusion
The hypotheses are (1) hyperpolarizing Na⁺ dynamics (decrease in intracellular Na⁺) and Na⁺‐driven secondary active transporters play a vital role in capacitation and (2) the sperm‐specific potassium channel Slo3 is involved in volume and/or morphological regulation.
... Thus, to gain further insights into the molecular makeup and orchestration of the signal transduction pathways in human sperm, kinetic multiplexed recordings of intracellular Ca 2+ , pH, and the membrane potential are required, using, for example, frequency-and spectrally-tuned multiplexing of fluorescent probes (FAST M ) (Kierzek et al., 2021) to investigate the chemosensory signal flow. The use of specific inhibitors for Slo3 channels (Lyon et al., 2023;Zhang et al., 2024) might allow to disentangle its role in chemosensory signalling. ...
To locate and fertilize the egg, sperm probe the varying microenvironment prevailing at different stages during their journey across the female genital tract. To this end, they are equipped with a unique repertoire of mostly sperm-specific proteins. In particular, the flagellar Ca²⁺ channel CatSper has come into focus as a polymodal sensor used by human sperm to register ligands released into the female genital tract. Here, we provide the first comprehensive study on the pharmacology of the sperm-specific human Slo3 channel, shedding light on its modulation by reproductive fluids and their constituents. We show that seminal fluid and contained prostaglandins and Zn²⁺ do not affect the channel, whereas human Slo3 is inhibited in a non-genomic fashion by diverse steroids as well as by albumin, which are released into the oviduct along with the egg. This indicates that not only CatSper but also Slo3 harbours promiscuous ligand-binding sites that can accommodate structurally diverse molecules, suggesting that Slo3 is involved in chemosensory signalling in human sperm.
... We aim to release annual updates with newly published compounds that modulate the function of spermatozoa. In our next release we aim to include compounds that were published during the collection of the data for this first release e.g., a sAC inhibitor TDI-11861 [4], a CatSper inhibitor RU1968 [66], a SLO3 inhibitor [67] or other contributions from the research community. The STB is a reference for compounds that modulate sperm function and can become an important resource for benchmarking new assays and new compounds. ...
Male contraceptive options and infertility treatments are limited, and almost all innovation has been limited to updates to medically assisted reproduction protocols and methods. To accelerate the development of drugs that can either improve or inhibit fertility, we established a small molecule library as a toolbox for assay development and screening campaigns using human spermatozoa. We have profiled all compounds in the Sperm Toolbox in several automated high-throughput assays that measure stimulation or inhibition of sperm motility or the acrosome reaction. We have assayed motility under non-capacitating and capacitating conditions to distinguish between pathways operating under these different physiological states. We also assayed cell viability to ensure any effects on sperm function are specific. A key advantage of our studies is that all compounds are assayed together in the same experimental conditions, which allows quantitative comparisons of their effects in complementary functional assays. We have combined the resulting datasets to generate fingerprints of the Sperm Toolbox compounds on sperm function. The data are included in an on-line R-based app for convenient querying.
... Like CatSper, SLO3 is specific to sperm and has functions essential for male fertility, making it an ideal target for male contraception [114][115][116]. A highly specific inhibitor of SLO3, VU0546110, has been identified and shown in vitro to inhibit sperm motility and acrosome reactions [117]. Better yet, at least one compound (termed "7 a" by Carlson et al. 2022) has been identified that blocks both SLO3 and CatSper, indicating potential for synergistic inhibition of sperm motility [111]. ...
Background
Since the release of the combined oral contraceptive pill in 1960, women have shouldered the burden of contraception and family planning. Over 60 years later, this is still the case as the only practical, effective contraceptive options available to men are condoms and vasectomy. However, there are now a variety of promising hormonal and non-hormonal male contraceptive options being studied. The purpose of this narrative review is to provide clinicians and laypeople with focused, up-to-date descriptions of novel strategies and targets for male contraception. We include a cautiously optimistic discussion of benefits and potential drawbacks, highlighting several methods in preclinical and clinical stages of development.
Results
As of June 2023, two hormonal male contraceptive methods are undergoing phase II clinical trials for safety and efficacy. A large-scale, international phase IIb trial investigating efficacy of transdermal segesterone acetate (Nestorone) plus testosterone gel has enrolled over 460 couples with completion estimated for late 2024. A second hormonal method, dimethandrolone undecanoate, is in two clinical trials focusing on safety, pharmacodynamics, suppression of spermatogenesis and hormones; the first of these two is estimated for completion in December 2024. There are also several non-hormonal methods with strong potential in preclinical stages of development.
Conclusions
There exist several hurdles to novel male contraception. Therapeutic development takes decades of time, meticulous work, and financial investment, but with so many strong candidates it is our hope that there will soon be several safe, effective, and reversible contraceptive options available to male patients.
... Expression of the human SLO3 alpha subunit by itself does not result in measurable whole-cell currents. Human SLO3 whole-cell currents can only be obtained in the presence of the human γ2 subunit [67,85,92]. The human SLO3 channel, even in the presence of the γ2 subunit, activates at more positive potentials than mouse or bovine SLO3 in Xenopus oocytes [67]. ...
... These discrepancies may be caused by the different recording conditions used [67,89]. We recently measured the effect of iberiotoxin on human SLO3 expressed in HEK-293 cells and found that it inhibited SLO3 at about 20-fold higher concentrations than SLO1 and had a much wider inhibition curve, making its inhibition of SLO3 currents highly susceptible to different recording conditions [92]. Paxilline, on the other hand, maintained a strong selectivity for SLO1 over human SLO3, as was observed in mice, making it a more useful tool for comparing the inhibition of SLO1 or SLO3 channels across species [92,107]. ...
... We recently measured the effect of iberiotoxin on human SLO3 expressed in HEK-293 cells and found that it inhibited SLO3 at about 20-fold higher concentrations than SLO1 and had a much wider inhibition curve, making its inhibition of SLO3 currents highly susceptible to different recording conditions [92]. Paxilline, on the other hand, maintained a strong selectivity for SLO1 over human SLO3, as was observed in mice, making it a more useful tool for comparing the inhibition of SLO1 or SLO3 channels across species [92,107]. ...
Sperm cells must undergo a complex maturation process after ejaculation to be able to fertilize an egg. One component of this maturation is hyperpolarization of the membrane potential to a more negative value. The ion channel responsible for this hyperpolarization, SLO3, was first cloned in 1998, and since then much progress has been made to determine how the channel is regulated and how its function intertwines with various signaling pathways involved in sperm maturation. Although Slo3 was originally thought to be present only in the sperm of mammals, recent evidence suggests that a primordial form of the gene is more widely expressed in some fish species. Slo3, like many reproductive genes, is rapidly evolving with low conservation between closely related species and different regulatory and pharmacological profiles. Despite these differences, SLO3 appears to have a conserved role in regulating sperm membrane potential and driving large changes in response to stimuli. The effect of this hyperpolarization of the membrane potential may vary among mammalian species just as the regulation of the channel does. Recent discoveries have elucidated the role of SLO3 in these processes in human sperm and provided tools to target the channel to affect human fertility.
... 42,43 This structure is the basis for the sensitivity of Slo1 to intracellular calcium ion concentration. However, in 2017, Geng et al. 44 found that Slo3 variants in humans differ from the wild type and are both sensitive to pH and Ca 2+ , and then Lyon et al. concluded that Slo3 is the sole K channel responsible for hyperpolarization in 2023, 45 meaning the controversy continues. ...
The ion channels in sperm tail play an important role in triggering key physiological reactions, e.g., progressive motility, hyperactivation, required for successful fertilization. Among them, CatSper and KSper have been shown to be important ion channels for the transport of Ca²⁺ and K⁺. Moreover, the voltage‐gated proton channel Hv1, the sperm‐specific sodium‐hydrogen exchanger (sNHE), the epithelial sodium channel (ENaC), members of the temperature‐sensitive TRP channel family, and the cystic fibrosis transmembrane regulator (CFTR) are also found in the flagellum. This review focuses on the latest advances in ion channels located at the flagellum, describes how they affect sperm physiological function, and summarizes some primary mutual regulation mechanism between ion channels, including PH, membrane potential, and cAMP. These ion channels may be promising targets for clinical application in infertility.
... Expression of the human SLO3 alpha subunit by itself does not result in measurable whole-cell currents. Human SLO3 whole-cell currents can only be obtained in the presence of the human γ2 subunit [65,83,90]. The human SLO3 channel, even in the presence of the γ2 subunit activates at more positive potentials than mouse or bovine SLO3 in Xenopus oocytes [65]. ...
... These discrepancies may be caused by different recording conditions used [65,87]. We recently measured the effect of iberiotoxin on human SLO3 expressed in HEK-293 cells and found that it inhibited SLO3 at about 20-fold higher concentrations than SLO1 and had a much wider inhibition curve, making its inhibition of SLO3 currents highly susceptible to different recording conditions [90]. Paxilline on the other hand maintained a strong selectivity for SLO1 over human SLO3, as was observed in mice, making it a more useful tool for comparing the inhibition of SLO1 or SLO3 channels across species [90,108]. ...
... We recently measured the effect of iberiotoxin on human SLO3 expressed in HEK-293 cells and found that it inhibited SLO3 at about 20-fold higher concentrations than SLO1 and had a much wider inhibition curve, making its inhibition of SLO3 currents highly susceptible to different recording conditions [90]. Paxilline on the other hand maintained a strong selectivity for SLO1 over human SLO3, as was observed in mice, making it a more useful tool for comparing the inhibition of SLO1 or SLO3 channels across species [90,108]. ...
Sperm cells must undergo a complex maturation process after ejaculation to be able to fertilize an egg. One component of this maturation is hyperpolarization of the membrane potential to a more negative value. The ion channel responsible for this hyperpolarization, SLO3, was first cloned in 1998, and since then much progress has been made to determine how the channel is regulated and how its function intertwines with various signaling pathways involved in sperm maturation. Although SLO3 was originally thought to be present only in the sperm of mammals, recent evidence suggests that a primordial form of the gene is more widely expressed in some fish species. As with many reproductive genes, SLO3 is rapidly evolving with low conservation between closely related species and different regulatory and pharmacological profiles. Despite these differences, SLO3 appears to have a conserved role in regulating sperm membrane potential and driving large changes in response to stimuli. As with the differences in regulation of the channel, the effect of this hyperpolarization of the membrane potential may vary among mammalian species. Recent discoveries have elucidated the role of SLO3 in these processes in human sperm and provided tools to target the channel to affect human fertility.
... Although additional studies are needed to pinpoint the molecular nature of the human KSper channel, it seems that its pore domain is composed of a combination of SLO3 and SLO1 (also known as KCNMA1) subunits (Ló pez-Gonzá lez et al., 2014;Sá nchez-Carranza et al., 2015). This hypothesis finds support in observations that (i) both SLO3 and SLO1 are present in the principal piece of the human sperm flagellum (Mannowetz et al., 2013;Brenker et al., 2014) and (ii) SLO3 and SLO1 selective inhibitors induce different levels of human I KSper inhibition, thus decreasing capacitation-induced hyperpolarization (Mannowetz et al., 2013;Brenker et al., 2014;Ló pez-Gonzá lez et al., 2014;Lyon et al., 2023). Human SLO3 sensitiveness to intracellular Ca 2þ is positively modulated by the auxiliary subunit LRRC52 and progesterone-induced CatSper activation (Brenker et al., 2014). ...
... Human SLO3 sensitiveness to intracellular Ca 2þ is positively modulated by the auxiliary subunit LRRC52 and progesterone-induced CatSper activation (Brenker et al., 2014). Using pharmacological tools, Lyon et al. (2023) recently provided compelling evidence that SLO3 is responsible for I KSper in human spermatozoa. By screening over 50 000 compounds for selective human SLO3 inhibitors, the authors identified the compound VU0456110, which showed over 40-fold higher potency to inhibit SLO3 than SLO1 (Figs 1B and 2). ...
... By screening over 50 000 compounds for selective human SLO3 inhibitors, the authors identified the compound VU0456110, which showed over 40-fold higher potency to inhibit SLO3 than SLO1 (Figs 1B and 2). In vitro exposure of human spermatozoa to VU0456110 blocked I KSper , thus pHi-induced membrane hyperpolarization and both A23187-and progesteroneinduced acrosome exocytosis (Lyon et al., 2023). ...
Background:
The high rates of unintended pregnancy and the ever-growing world population impose health, economic, social, and environmental threats to countries. Expanding contraceptive options, including male methods, are urgently needed to tackle these global challenges. Male contraception is limited to condoms and vasectomy, which are unsuitable for many couples. Thus, novel male contraceptive methods may reduce unintended pregnancies, meet the contraceptive needs of couples, and foster gender equality in carrying the contraceptive burden. In this regard, the spermatozoon emerges as a source of druggable targets for on-demand, non-hormonal male contraception based on disrupting sperm motility or fertilization.
Objective and rationale:
A better understanding of the molecules governing sperm motility can lead to innovative approaches toward safe and effective male contraceptives. This review discusses cutting-edge knowledge on sperm-specific targets for male contraception, focusing on those with crucial roles in sperm motility. We also highlight challenges and opportunities in male contraceptive drug development targeting spermatozoa.
Search methods:
We conducted a literature search in the PubMed database using the following keywords: 'spermatozoa', 'sperm motility', 'male contraception', and 'drug targets' in combination with other related terms to the field. Publications until January 2023 written in English were considered.
Outcomes:
Efforts for developing non-hormonal strategies for male contraception resulted in the identification of candidates specifically expressed or enriched in spermatozoa, including enzymes (PP1γ2, GAPDHS, and sAC), ion channels (CatSper and KSper), transmembrane transporters (sNHE, SLC26A8, and ATP1A4), and surface proteins (EPPIN). These targets are usually located in the sperm flagellum. Their indispensable roles in sperm motility and male fertility were confirmed by genetic or immunological approaches using animal models and gene mutations associated with male infertility due to sperm defects in humans. Their druggability was demonstrated by the identification of drug-like small organic ligands displaying spermiostatic activity in preclinical trials.
Wider implications:
A wide range of sperm-associated proteins has arisen as key regulators of sperm motility, providing compelling druggable candidates for male contraception. Nevertheless, no pharmacological agent has reached clinical developmental stages. One reason is the slow progress in translating the preclinical and drug discovery findings into a drug-like candidate adequate for clinical development. Thus, intense collaboration among academia, private sectors, governments, and regulatory agencies will be crucial to combine expertise for the development of male contraceptives targeting sperm function by (i) improving target structural characterization and the design of highly selective ligands, (ii) conducting long-term preclinical safety, efficacy, and reversibility evaluation, and (iii) establishing rigorous guidelines and endpoints for clinical trials and regulatory evaluation, thus allowing their testing in humans.
... The identity of the main K + channel in humans is suggested to be Slo1 [13]. Slo3 in human spermatozoa also plays a vital role in sperm physiology, as homozygous mutations in Slo3 result in severe asthenozoospermia and selective inhibition impairs sperm function [18,21,22]. In mice, electrophysiological data favor Slo3 as the principal route of K + conductance [9,23]. ...
Sperm ion channels are associated with the quality and type of flagellar movement, and their differential regulation is crucial for sperm function during specific phases. The principal potassium ion channel is responsible for the majority of K⁺ ion flux, resulting in membrane hyperpolarization, and is essential for sperm capacitation-related signaling pathways. The molecular identity of the principal K⁺ channel varies greatly between different species, and there is a lack of information about boar K⁺ channels. We aimed to determine the channel identity of boar sperm contributing to the primary K⁺ current using pharmacological dissection. A series of Slo1 and Slo3 channel modulators were used for treatment. Sperm motility and related kinematic parameters were monitored using a computer-assisted sperm analysis system under non-capacitated conditions. Time-lapse flow cytometry with fluorochromes was used to measure changes in different intracellular ionic concentrations, and conventional flow cytometry was used to determine the acrosome reaction. Membrane depolarization, reduction in acrosome reaction, and motility parameters were observed upon the inhibition of the Slo3 channel, suggesting that the Slo3 gene encodes the main K⁺ channel in boar spermatozoa. The Slo3 channel was localized on the sperm flagellum, and the inhibition of Slo3 did not reduce sperm viability. These results may aid potential animal-model-based extrapolations and help to ameliorate motility and related parameters, leading to improved assisted reproductive methods in industrial livestock production.
... The SLO3 K + channel has previously been shown to be essential for mediating the hyperpolarization observed in capacitated mouse sperm [56]. A recent study utilized a novel specific inhibitor of the human SLO3 K + channel, VU0546110, that prevented human sperm from hyperpolarizing and undergoing hyperactivated activity, and prevented the Ca 2+ -or progesterone-induced acrosome reaction [57]. Interestingly, a study using human sperm found no evidence of alkalization of either the sperm head or flagellum in response to valinomycin-induced hyperpolarization [26], suggesting a potential different role of NHE10 and/or NHE11 in human sperm as compared to sea urchin sperm, in which the suSLC9C protein was shown to be responsible for the hyperpolarization-evoked alkalization in response to speract stimulation [19]. ...
Na⁺/H⁺ exchangers (NHEs) are a family of ion transporters that regulate the pH of various cell compartments across an array of cell types. In eukaryotes, NHEs are encoded by the SLC9 gene family comprising 13 genes. SLC9C2, which encodes the NHE11 protein, is the only one of the SLC9 genes that is essentially uncharacterized. Here, we show that SLC9C2 exhibits testis/sperm-restricted expression in rats and humans, akin to its paralog SLC9C1 (NHE10). Similar to NHE10, NHE11 is predicted to contain an NHE domain, a voltage sensing domain, and finally an intracellular cyclic nucleotide binding domain. An immunofluorescence analysis of testis sections reveals that NHE11 localizes with developing acrosomal granules in spermiogenic cells in both rat and human testes. Most interestingly, NHE11 localizes to the sperm head, likely the plasma membrane overlaying the acrosome, in mature sperm from rats and humans. Therefore, NHE11 is the only known NHE to localize to the acrosomal region of the head in mature sperm cells. The physiological role of NHE11 has yet to be demonstrated but its predicted functional domains and unique localization suggests that it could modulate intracellular pH of the sperm head in response to changes in membrane potential and cyclic nucleotide concentrations that are a result of sperm capacitation events. If NHE11 is shown to be important for male fertility, it will be an attractive target for male contraceptive drugs due to its exclusive testis/sperm-specific expression.
