K M Sanders

University of Nevada, Reno, Reno, Nevada, United States

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Publications (368)1730.11 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Four types of electrical activity were recorded and related to cell structure by intracellular recording and dye injection into impaled cells in muscles of rabbit small intestine. The specific cell-types from which recordings were made were longitudinal smooth muscle cells (LSMCs), circular smooth muscle cells (CSMCs), interstitial cells of Cajal distributed in the myenteric region (ICC-MY) and fibroblast-like cells (FLCs). Slow waves (slow wavesSMC) were recorded from LSMCs and CSMCs. Slow waves (slow wavesICC) were of greatest amplitude (>50 mV) and highest maximum rate-of-rise (> 10 V s−1) in ICC. The dominant activity in FLCs was spontaneous transient hyperpolarizations (STHs), with maximum amplitudes more than 30 mV. STHs were often superimposed upon small amplitude slow waves (slow wavesFLC). STHs displayed a cyclical patterned discharge irrespective of background slow wave activity. STHs were inhibited by MRS2500 (3 μM), a P2Y1 antagonist, and abolished by apamin (0.3 μM), a blocker of small conductance Ca2+-activated K+ (SK) channels. Small amplitude STHs (< 15 mV) were detected in smooth muscle layers, whereas STHs were not resolved in cells identified as ICC-MY. Electrical field stimulation (EFS) evoked purinergic inhibitory junction potentials (IJPs) in CSMCs. Purinergic IJPs were not recorded from ICC-MY. These results suggest that FLCs may regulate smooth muscle excitability in the rabbit small intestine via generation of rhythmic apamin-sensitive STHs. Stimulation of P2Y1 receptors modulates the amplitudes of STHs. Our results also suggest that purinergic inhibitory motor neurons regulate the motility of the rabbit small intestine by causing IJPs in FLCs that conduct to CSMCs.This article is protected by copyright. All rights reserved
    The Journal of Physiology 09/2014; · 4.38 Impact Factor
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    ABSTRACT: Enteric inhibitory neurotransmission is an important feature of the neural regulation of gastrointestinal (GI) motility. Purinergic neurotransmission, via P2Y1 receptors, mediates one phase of inhibitory neural control. For decades ATP has been assumed to be the purinergic neurotransmitter and smooth muscle cells (SMCs) have been considered the primary targets for inhibitory neurotransmission. Recent experiments have cast doubt upon both of these assumptions and suggested another cell type, PDGFRα(+) cells, as the target for purinergic neurotransmission. We compared responses of PDGFRα(+) cells and SMCs to several purine compounds to determine if these cells responded in a manner consistent with enteric inhibitory neurotransmission. ATP hyperpolarized PDGFRα(+) cells but depolarized SMCs. Only part of the ATP response in PDGFRα(+) cells was blocked by MRS2500, a P2Y1 antagonist. ADP, MRS2365, β-NAD and ADPR (P2Y1 agonists) hyperpolarized PDGFRα(+) cells, and these responses were blocked by MRS2500. ADPR was more potent in eliciting hyperpolarization responses than β-NAD. P2Y1 agonists failed to elicit responses in SMCs. Small hyperpolarization responses were elicited in SMCs by an SK channel agonist, CyPPA, consistent with the low expression and current density of SK channels in these cells. Large amplitude hyperpolarization responses, elicited in PDGFRα(+) cells but not SMCs by P2Y1 agonists, are consistent with the generation of inhibitory junction potentials in intact muscles in response to purinergic neurotransmission. The responses of PDGFRα(+) cells and SMCs to purines suggest that SMCs are unlikely targets for purinergic neurotransmission in colonic muscles.
    American journal of physiology. Cell physiology. 07/2014;
  • Kenton M Sanders, Sean M Ward, Sang Don Koh
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    ABSTRACT: Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.
    Physiological reviews. 07/2014; 94(3):859-907.
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    ABSTRACT: Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha (PDGFRα+) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRα+ cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.
    Journal of neurogastroenterology and motility 06/2014;
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    ABSTRACT: Several motility disorders are associated with disruption of interstitial cells of Cajal (ICC), which provide important functions, such as pacemaker activity, mediation of neural inputs and responses to stretch in the gastrointestinal (GI) tract. Restoration of ICC networks may be therapeutic for GI motor disorders. Recent reports have suggested that Kit(+) cells can be restored to the GI tract via bone marrow (BM) transplantation. We tested whether BM derived cells can lead to generation of functional activity in intestines naturally lacking ICC.
    Journal of neurogastroenterology and motility 05/2014;
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    ABSTRACT: Interstitial cells of Cajal (ICC) play important functions in motor activity of the gastrointestinal tract. The role of ICC as pace-makers is well established, however their participation in neurotransmission is controversial. Studies using mutant animals that lack ICC have yielded variable conclusions on their importance in enteric motor responses. The purpose of this study was to: (1) clarify the role of intramuscular ICC (ICC-IM) in gastric motor-neurotransmission and (2) evaluate remodeling of enteric mo-tor responses in W/W(V) mice.
    Journal of neurogastroenterology and motility 04/2014; 20(2):171-84.
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    ABSTRACT: Interstitial cells of Cajal (ICC) generate slow waves in gastrointestinal (GI) muscles. Previous studies have suggested that slow wave generation and propagation depends upon a voltage-dependent Ca(2+) entry mechanism with the signature of a T-type Ca(2+) conductance. We studied voltage-dependent inward currents in isolated ICC. ICC displayed two phases of inward current upon depolarization: a low voltage-activated inward current and a high voltage-activated current. The latter was of smaller current density and blocked by nicardipine. Ni(2+) (30μM) or mibefradil (1μM) blocked the low voltage-activated current. Replacement of extracellular Ca(2+) with Ba(2+) did not affect the current, suggesting that either charge carrier was equally permeable. Half-activation and half-inactivation occurred at -36 mV and -59 mV, respectively. Temperature sensitivity of the Ca(2+) current was also characterized. Increasing temperature (20° to 30°C) augmented peak current from -7 to -19 pA and decreased the activation time from 20.6 to 7.5 ms (Q10=3.0). Molecular studies showed expression of Cacna1g (Cav3.1) and Cacna1h (Cav3.2) in ICC. The temperature dependence of slow waves in intact jejunal muscles of wildtype and Cacna1h(-/-) mice was tested. Reducing temperature decreased the upstroke velocity significantly. Upstroke velocity was also reduced in muscles of Cacna1h(-/-) mice and Ni(2+) or reduced temperature had little effect on these muscles. Our data show that a T-type conductance is expressed and functional in ICC. With previous studies our data suggest that T-type current is required for entrainment of pacemaker activity within ICC and for active propagation of slow waves in ICC networks.
    AJP Cell Physiology 01/2014; · 3.71 Impact Factor
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    ABSTRACT: 5-Hydroxytryptamine (5-HT, serotonin) is an important regulator of colonic motility and secretion; yet the role of serotonergic neurons in the colon is controversial. We used immunohistochemical techniques to examine their projections throughout the enteric nervous system and interstitial cells of Cajal (ICC) networks in the murine proximal to mid colon. Serotonergic neurons, which were mainly calbindin positive, occurred only in myenteric ganglia (1 per 3 ganglia). They were larger than nNOS neurons but similar in size to Dogiel Type II (AH) neurons. 5-HT neurons, appeared to make numerous varicose contacts with each other, most nNOS neurons, Dogiel Type II/AH neurons and glial cells. 5-HT, calbindin and nNOS nerve fibers also formed a thin perimuscular nerve plexus that was associated with ganglia, which contained both nNOS positive and negative neurons, which lay directly upon the submucosal pacemaker ICC network. Neurons in perimuscular ganglia were surrounded by 5-HT varicosities. Submucous ganglia contained nNOS positive and negative neurons, and calbindin positive neurons, which also appeared richly supplied by serotonergic nerve varicosities. Serotonergic nerve fibers ran along submucosal arterioles, but not veins. Varicosities of serotonergic nerve fibers were closely associated with pacemaker ICC networks and with intramuscular ICC (ICC-IM). 5-HT2B receptors were found on a subpopulation of non-5-HT containing myenteric neurons and their varicosities, pacemaker ICC-MY and ICC-IM. Myenteric serotonergic neurons, whose axons exhibit considerable divergence, regulate the entire enteric nervous system and are important in coordinating motility with secretion. They are not just interneurons, as regularly assumed, but possibly also motor neurons to ICC and blood vessels, and some may even be sensory neurons.
    Neurogastroenterology and Motility 01/2014; · 2.94 Impact Factor
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    ABSTRACT: Purines induce transient contraction and prolonged relaxation of detrusor muscles. Transient contraction could be due to activation of inward currents in smooth muscle cells, but the mechanism of purinergic relaxation has not been determined. We recently reported a new class of interstitial cells in detrusor muscles and showed these cells could be identified with antibodies against platelet-derived growth factor receptor-α (PDGFRα(+) cells). The current density of small conductance Ca(2+)-activated K(+) (SK) channels in these cells is far higher (~100 times) than in smooth muscle cells. Thus, we examined P2Y receptor-mediated SK channel activation as a mechanism for purinergic relaxation. P2Y receptors (mainly P2ry1) were highly expressed in PDGFRα(+) cells. Under voltage clamp conditions ATP activated large outward currents in PDGFRα(+) cellsthat were inhibited by blockers of SK channels. ATP also induced significant hyperpolarization under current clamp conditions. A P2Y1 agonist, MRS2365, mimicked the effects of ATP, and a P2Y1 antagonist, MRS2500, inhibited ATP-activated SK currents. Responses to ATP were largely abolished in PDGFRα(+) cells of P2ry1(-/-) mice, and no response was elicited by MRS2365 in these cells. A P2X receptor agonist had no effect on PDGFRα(+) cells but, like ATP, activated transient inward currents in SMCs. A P2Y1 antagonist decreased nerve-evoked relaxation. These data suggest that purines activate SK currents via mainly P2Y1 receptor in PDGFRα+ cells. Our findings provide an explanation for purinergic relaxation in detrusor muscles and show that while there are not discrete inhibitory nerve fibers. A dual receptive field for purines provides the basis for inhibitory neural regulation of excitability.
    The Journal of Physiology 01/2014; · 4.38 Impact Factor
  • Kenton M Sanders, Bhupal P Bhetwal, Brian A Perrino
    The Journal of Physiology 11/2013; 591(Pt 21):5415-6. · 4.38 Impact Factor
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    ABSTRACT: Platelet Derived Growth Factor Receptor α positive (PDGFRα+) cells are suggested to mediate purinergic inputs in GI muscles, but responsiveness of these cells to purines in situ has not been evaluated. We developed techniques to label and visualize PDGFRα+ cells in murine gastric fundus, load cells with Ca2+ indicators, and follow their activity via digital imaging. Immuno-labeling demonstrated a high density of PDGFRα+ cells in the fundus. Cells were isolated and purified by FACS using endogenous expression of eGFP driven off the Pdgfra promoter. Quantitative PCR showed high levels of expression of P2Y1 receptors and SK3 channels in PDGFRα+ cells. Ca2+ imaging was used to characterize spontaneous Ca2+ transients and responses to purines in PDGFRα+ cells in situ. ATP, ADP, UTP and β-NAD elicited robust Ca2+ transients in PDGFRα+ cells. Ca2+ transients were also elicited by the P2Y1-specific agonist N)-methanocarba-2MeSADP (MRS-2365), and inhibited by MRS-2500, a P2Y1-specific antagonist. Responses to ADP, MRS-2365 and β-NAD were absent in PDGFRα+ cells from P2ry1(-/-) mice, but responses to ATP were retained. Purine evoked Ca2+ transients were mediated through Ca2+ release mechanisms. Inhibitors of PLC (U-73122), IP3 and ryanodine receptors, SERCA pump (cyclopiazonic acid (CPA) and thapsigargin) abolished Ca2+ transients elicited by purines. This study provides a link between purine binding to P2Y1 receptors and activation of SK3 channels in PDGFRα+ cells. Activation of Ca2+ release is likely to be the signaling mechanism in PDGFRα+ cells responsible for transduction of purinergic enteric inhibitory input in gastric fundus muscles.
    The Journal of Physiology 10/2013; · 4.38 Impact Factor
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    ABSTRACT: Purinergic signaling provides regulation of colonic motility. Smooth muscle cells (SMC), interstitial cells of Cajal (ICC), and platelet-derived growth factor receptor α-positive (PDGFRα(+) ) cells are electrically coupled and form a functional (SIP) syncytium that constitutes the receptive field for motor neurotransmitters in the tunica muscularis. Each cell type in the SIP syncytium has specialized functions in mediating motor neurotransmission. We compared gene transcripts for purinergic receptors and membrane-bound enzymes for purine degradation expressed by each cell type of the SIP syncytium. Fluorescence-activated cell sorting (FACS) was used to purify SMC, ICC, and PDGFRα(+) cells from mixed cell populations of colonic muscles dispersed from reporter strains of mice with constitutive expression of green fluorescent proteins. Differential expression of functional groups of genes related to purinergic signaling was determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). We detected marked phenotypic differences among SMC, ICC, and PDGFRα(+) cells. Substantial numbers of genes of importance in purinergic neurotransmission were enriched in PDGFRα(+) cells in relation to SMC and ICC. Notably, genes related to mediating effects and extracellular biotransformation of enteric purinergic inhibitory neurotransmitters were strongly expressed by PDGFRα(+) cells. Our results demonstrate differential expression of genes for proteins involved in purinergic signaling in the SIP syncytium. These results may further clarify the specific functions of each cell type, identify novel biomarkers for postjunctional cells, and provide hypotheses for further studies to understand the physiological roles of cells of the SIP syncytium.
    Neurogastroenterology and Motility 06/2013; · 2.94 Impact Factor
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    ABSTRACT: BACKGROUND: Loss or disruption of Kit(+) -interstitial cells of Cajal (ICC) capable of generating pacemaker activity has been implicated in the development of numerous gastrointestinal motility disorders. We sought to develop a model where ICC could be allotransplanted into intestines naturally devoid of these cells. METHODS: Enzymatically dispersed cells from the intestinal tunica muscularis of Kit(+/copGFP) and Kit(V558Δ) /+ gain-of-function mice were allotransplanted into myenteric plexus regions of W/W(V) mutant intestines that lack ICC at the level of the myenteric plexus (ICC-MY) and pacemaker activity. Immunohistochemical analysis fate mapped the development of ICC-MY networks and intracellular microelectrode recordings provided evidence for the development of functional pacemaker activity. KEY RESULTS: Kit(+) -ICC developed into distinct networks at the level of the myenteric plexus in organotypic cultures over 28 days and displayed robust rhythmic pacemaker activity. CONCLUSIONS & INFERENCES: This study demonstrates the feasibility of allotransplantation of ICC into the myenteric region of the small intestine and the establishment of functional pacemaker activity into tissues normally devoid of ICC-MY and slow waves, thus providing a possible basis for the therapeutic treatment of patients where ICC networks have been disrupted due to a variety of pathophysiological conditions.
    Neurogastroenterology and Motility 05/2013; · 2.94 Impact Factor
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    ABSTRACT: Ca(2+) sensitization of contraction has typically been investigated by bathing muscles in solutions containing agonists. However, it is unknown whether bath applied agonists and enteric neurotransmission activate similar Ca2+ sensitization mechanisms. We investigated protein kinase c (PKC)-potentiated phosphatase inhibitor protein of 17 kDa (CPI-17) and myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation in murine gastric fundus muscles stimulated by bath-applied carbachol (CCh) or cholinergic motor neurotransmission. CCh increased MYPT1 phosphorylation at T696 (pT696) and T853 (pT853), CPI-17 at T38 (pT38), and myosin light chain at S19 (pS19). Electrical field stimulation (EFS) only increased pT38. In the presence of neostigmine, EFS increased pT38, pT853, and pS19. In fundus muscles of W/Wv mice, EFS alone increased pT38 and pT853. Atropine blocked all contractions and all increases in pT696, pT853, pT38, and pS19. The Rho kinase (ROCK) inhibitor SAR1x blocked increases in pT853 and pT696. The PKC inhibitors Go6976 and Gf109203x or nicardipine blocked increases in pT38 and pT696. These findings suggest that cholinergic motor neurotransmission activates PKC-dependent CPI-17 phosphorylation. Bath-applied CCh recruits additional ROCK-dependent MYPT1 phosphorylation due to exposure of the agonist to a wider population of muscarinic receptors. Intramuscular interstitial cells of Cajal (ICC-IM) and cholinesterases restrict ACh accessibility to a select population of muscarinic receptors, possibly only those expressed by ICC-IM. These results provide the first biochemical evidence for focalized (or synaptic-like) neurotransmission, rather than diffuse 'volume' neurotransmission in a smooth muscle tissue. Furthermore, these findings demonstrate that bath application of contractile agonists to gastrointestinal (GI) smooth muscles does not mimic physiological responses to cholinergic neurotransmission.
    The Journal of Physiology 04/2013; · 4.38 Impact Factor
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    ABSTRACT: Recently platelet-derived growth factor α-positive cells (PDGFRα(+) cells), previously called 'fibroblast-like' cells, have been described in the muscle layers of the gastrointestinal (GI) tract. These cells form networks and are involved in purinergic motor neurotransduction. Examination of colon from mice with eGFP driven from the endogenous Pdgfra (PDGFRα-eGFP mice) revealed a unique population of PDGFRα(+) cells in the mucosal layer of colon. We investigated the phenotype and potential role of these cells, which have not been characterized previously. Expression of PDGFRα and several additional proteins were surveyed in human and murine colonic mucosae by immuno-labeling, PDGFRα(+) cells in colonic mucosa were isolated from PDGFRα-eGFP mice, and the gene expression profile was analyzed by quantitative polymerase chain reaction. We found for the first time that PDGFRα was expressed in subepithelial cells (subepithelial PDGFRα(+) cells) forming a pericryptal sheath from the base to the tip of crypts. These cells were in close proximity to the basolateral surface of epithelial cells and distinct from subepithelial myofibroblasts, which were identified by expression of α smooth muscle actin and smooth muscle myosin. PDGFRα(+) cells also lay in close proximity to varicose processes of nerve fibers. Mouse subepithelial PDGFRα(+) cells expressed Toll-like receptor genes, purinergic receptor genes, 5-HT4 receptor gene and Hedgehog signaling genes. Subepithelial PDGFRα(+) cells occupy an important niche in the lamina propria and may function in transduction of sensory and immune signals and in the maintenance of mucosal homeostasis.
    AJP Gastrointestinal and Liver Physiology 02/2013; · 3.65 Impact Factor
  • K-J Won, K M Sanders, S M Ward
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    ABSTRACT: Background  The colon undergoes distension-induced changes in motor activity as luminal contents or feces increase wall pressure. Input from enteric motor neurons regulates this motility. Here we examined stretch-dependent responses in circular muscle strips of murine colon. Methods  Length ramps (6-31μm s(-1) ) were applied in the axis of the circular muscle layer in a controlled manner until 5 mN isometric force was reached. Key Results  Length ramps produced transient membrane potential hyperpolarizations and attenuation of action potential (AP) complexes. Responses were reproducible when ramps were applied every 30 s. Stretch-dependent hyperpolarization was blocked by TTX, suggesting AP-dependent release of inhibitory neurotransmitter(s). Atropine did not potentiate stretch-induced hyperpolarizations, but increased compliance of the circular layer. N(ω) -nitro-l-arginine (l-NNA) inhibited stretch-dependent hyperpolarization and decreased muscle compliance, suggesting release of NO mediates stretch-dependent inhibition. Control membrane potential was restored by the NO donor sodium nitorprusside. Stretch-dependent hyperpolarizations were blocked by l-methionine, an inhibitor of stretch-dependent K(+) (SDK) channels in colonic muscles. Loss of interstitial cells of Cajal, elicited by Kit neutralizing antibody, also inhibited responses to stretch. In presence of l-NNA and apamin, stretch responses became excitatory and were characterized by membrane depolarization and increased AP firing. A neurokinin-1 receptor antagonist inhibited this stretch-dependent increase in excitability. Conclusions and Inferences  Our data show that stretch-dependent responses in colonic muscles require tonic firing of enteric inhibitory neurons, but reflex activation of neurons does not appear to be necessary. NO causes activation of SDK channels, and stretch of muscles further activates these channels, explaining the inhibitory response to stretch in colonic muscle strips.
    Neurogastroenterology and Motility 01/2013; · 2.94 Impact Factor
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    ABSTRACT: Background  The purinergic component of enteric inhibitory neurotransmission is important for normal motility in the gastrointestinal (GI) tract. Controversies exist about the purine(s) responsible for inhibitory responses in GI muscles: ATP has been assumed to be the purinergic neurotransmitter released from enteric inhibitory motor neurons; however, recent studies demonstrate that β-nicotinamide adenine dinucleotide (β-NAD(+) ) and ADP-ribose mimic the inhibitory neurotransmitter better than ATP in primate and murine colons. The study was designed to clarify the sources of purines in colons of Cynomolgus monkeys and C57BL/6 mice. Methods  High-performance liquid chromatography with fluorescence detection was used to analyze purines released by stimulation of nicotinic acetylcholine receptors (nAChR) and serotonergic 5-HT(3) receptors (5-HT(3) R), known to be present on cell bodies and dendrites of neurons within the myenteric plexus. Key Results  Nicotinic acetylcholine receptor or 5-HT(3) R agonists increased overflow of ATP and β-NAD(+) from tunica muscularis of monkey and murine colon. The agonists did not release purines from circular muscles of monkey colon lacking myenteric ganglia. Agonist-evoked overflow of β-NAD(+) , but not ATP, was inhibited by tetrodotoxin (0.5 μmol L(-1) ) or ω-conotoxin GVIA (50 nmol L(-1) ), suggesting that β-NAD(+) release requires nerve action potentials and junctional mechanisms known to be critical for neurotransmission. ATP was likely released from nerve cell bodies in myenteric ganglia and not from nerve terminals of motor neurons. Conclusions & Inferences  These results support the conclusion that ATP is not a motor neurotransmitter in the colon and are consistent with the hypothesis that β-NAD(+) , or its metabolites, serve as the purinergic inhibitory neurotransmitter.
    Neurogastroenterology and Motility 01/2013; · 2.94 Impact Factor
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    ABSTRACT: We sought to characterize molecular expression and ionic conductances in a novel population of interstitial cells (PDGFRα+ cells) in murine bladder to determine how these cells might participate in regulation of detrusor excitability. PDGFRα+ cells and smooth muscle cells (SMCs) were isolated from detrusor muscles of PDGFR&α(+)/eGFP and smMHC/Cre/eGFP mice and sorted by FACS. PDGFRα(+) cells were highly enriched in Pdgfra (12 fold vs. unsorted cell) and minimally positive for Mhc (SMC marker), Kit (ICC marker) and Pgp9.5 (neuronal marker). SK3 was dominantly expressed in PDGFRα(+) cells in comparison to SMCs. αSlo (BK marker) was more highly expressed in SMCs. SK3 protein was observed in PDGFRα(+) cells by immunohistochemistry but could not be resolved in SMCs. Depolarization evoked voltage-dependent (Ca2+) currents in SMCs, but inward current conductances were not activated in PDGFRα(+) cells under the same conditions. PDGFRα(+) cells displayed spontaneous transient outward currents (STOCs) at potentials positive to -60 mV that were inhibited by apamin. SK channel modulators, CyPPA and SKA-31, induced significant hyperpolarization of PDGFRα(+) cells and activated SK currents under voltage clamp. Similar responses were not resolved in SMCs at physiological potentials. Single channel measurements confirmed the presence of functional SK3 channels (i.e. single channel conductance of 10 pS and sensitivity to intracellular Ca(2+)) in PDGFRα(+) cells. The apamin-sensitive stabilizing factor regulating detrusor excitability is likely to be due to the expression of SK3 channels in PDGFRα(+) cells because SK agonists failed to elicit resolvable currents and hyperpolarization in SMCs at physiological potentials.
    The Journal of Physiology 11/2012; · 4.38 Impact Factor
  • Kenton M Sanders, Sang Don Koh, Seungil Ro, Sean M Ward
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    ABSTRACT: Gastrointestinal motility results from coordinated contractions of the tunica muscularis, the muscular layers of the alimentary canal. Throughout most of the gastrointestinal tract, smooth muscles are organized into two layers of circularly or longitudinally oriented muscle bundles. Smooth muscle cells form electrical and mechanical junctions between cells that facilitate coordination of contractions. Excitation-contraction coupling occurs by Ca(2+) entry via ion channels in the plasma membrane, leading to a rise in intracellular Ca(2+). Ca(2+) binding to calmodulin activates myosin light chain kinase; subsequent phosphorylation of myosin initiates cross-bridge cycling. Myosin phosphatase dephosphorylates myosin to relax muscles, and a process known as Ca(2+) sensitization regulates the activity of the phosphatase. Gastrointestinal smooth muscles are 'autonomous' and generate spontaneous electrical activity (slow waves) that does not depend upon input from nerves. Intrinsic pacemaker activity comes from interstitial cells of Cajal, which are electrically coupled to smooth muscle cells. Patterns of contractile activity in gastrointestinal muscles are determined by inputs from enteric motor neurons that innervate smooth muscle cells and interstitial cells. Here we provide an overview of the cells and mechanisms that generate smooth muscle contractile behaviour and gastrointestinal motility.
    Nature Reviews Gastroenterology &#38 Hepatology 09/2012; · 10.43 Impact Factor
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    ABSTRACT: Kit immunohistochemistry and confocal reconstructions have provided detailed 3-dimensional images of ICC networks throughout the gastrointestinal (GI) tract. Morphological criteria have been used to establish that different classes of ICC exist within the GI tract and physiological studies have shown that these classes have distinct physiological roles in GI motility. Structural studies have focused predominately on rodent models and less information is available on whether similar classes of ICC exist within the GI tracts of humans or non-human primates. Using Kit immunohistochemistry and confocal imaging, we examined the 3-dimensional structure of ICC throughout the GI tract of cynomolgus monkeys. Whole or flat mounts and cryostat sections were used to examine ICC networks in the lower esophageal sphincter (LES), stomach, small intestine and colon. Anti-histamine antibodies were used to distinguish ICC from mast cells in the lamina propria. Kit labeling identified complex networks of ICC populations throughout the non-human primate GI tract that have structural characteristics similar to that described for ICC populations in rodent models. ICC-MY formed anastomosing networks in the myenteric plexus region. ICC-IM were interposed between smooth muscle cells in the stomach and colon and were concentrated within the deep muscular plexus (ICC-DMP) of the intestine. ICC-SEP were found in septal regions of the antrum that separated circular muscle bundles. Spindle-shaped histamine(+) mast cells were found in the lamina propria throughout the GI tract. Since similar sub-populations of ICC exist within the GI tract of primates and rodents and the use of rodents to study the functional roles of different classes of ICC is warranted.
    Cell and Tissue Research 08/2012; 350(2):199-213. · 3.68 Impact Factor

Publication Stats

11k Citations
1,730.11 Total Impact Points

Institutions

  • 1992–2014
    • University of Nevada, Reno
      • • Department of Physiology and Cell Biology
      • • School of Medicine
      Reno, Nevada, United States
  • 2013
    • Konkuk University
      Sŏul, Seoul, South Korea
  • 1986–2012
    • University of Nevada School of Medicine
      • Department of Pharmacology
      Reno, Nevada, United States
  • 2009
    • Queen's University Belfast
      Béal Feirste, N Ireland, United Kingdom
    • University of Fukui
      • Department of Morphological and Physiological Sciences
      Hukui, Fukui, Japan
  • 2005
    • Seoul National University
      • Department of Surgery
      Seoul, Seoul, South Korea
    • Ulsan University Hospital
      Urusan, Ulsan, South Korea
  • 2003–2004
    • University of Yamanashi
      • Division of Medicine
      Kōhu, Yamanashi, Japan
  • 2002
    • Tokai University
      • School of Medicine
      Hiratsuka, Kanagawa-ken, Japan
  • 1998–2002
    • University of Melbourne
      • Department of Zoology
      Melbourne, Victoria, Australia
  • 1999
    • Nagoya University
      Nagoya, Aichi, Japan
  • 1996
    • Hanyang University
      • Department of Medicine
      Ansan, Gyeonggi, South Korea
    • University of Illinois, Urbana-Champaign
      Urbana, Illinois, United States