Murine Interstitial Cells Of Cajal Research Articles

P.760 Effects of novel cholinesterase inhibitors on mitochondrial respiration and MAO activity - in vitro study

Based on the lately identified role for the interstitial cells of Cajal (ICCs) of mouse prostate in catecholamine production, as well as the well-established role for the master coregulator metastasis-associated protein 1 (MTA1) in inflammation, we probed into the functional link between aberrant MTA1 expression and pathogenesis of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) using both a MTA1−/− mouse model of experimental autoimmune prostatitis (EAP) and an in vitro chronic prostatitis model in cultured murine ICCs. EAP-induced MTA1 expression was enriched in ICCs of mouse prostate. EAP resulted in a higher increase in the pelvic pain response in MTA1−/− mice compared to WT mice. Consistently, the ICCs from MTA1−/− mice produced higher levels of catecholamines upon induction of in vitro chronic prostatitis. Mechanistically, MTA1 could directly suppress the transcription of Aadc, a rate-limiting enzyme during catecholamine synthesis, in a HDAC2-depdendent manner. Importantly, treatment with AADC inhibitor NSD-1015 significantly ameliorated EAP-elicited pain response and catecholamine overactivity in MTA1−/− mice. Taken together, our findings reveal an inherent regulatory role of the MTA1/AADC pathway in the maintenance of catecholamine production homeostasis in prostate ICCs, and also point to a potential use of HDAC inhibitors and/or AADC inhibitors to treat CP/CPPS.

Understanding the Biology of Human Interstitial Cells of Cajal in Gastrointestinal Motility

Millions of patients worldwide suffer from gastrointestinal (GI) motility disorders such as gastroparesis. These disorders typically include debilitating symptoms, such as chronic nausea and vomiting. As no cures are currently available, clinical care is limited to symptom management, while the underlying causes of impaired GI motility remain unaddressed. The efficient movement of contents through the GI tract is facilitated by peristalsis. These rhythmic slow waves of GI muscle contraction are mediated by several cell types, including smooth muscle cells, enteric neurons, telocytes, and specialised gut pacemaker cells called interstitial cells of Cajal (ICC). As ICC dysfunction or loss has been implicated in several GI motility disorders, ICC represent a potentially valuable therapeutic target. Due to their availability, murine ICC have been extensively studied at the molecular level using both normal and diseased GI tissue. In contrast, relatively little is known about the biology of human ICC or their involvement in GI disease pathogenesis. Here, we demonstrate human gastric tissue as a source of primary human cells with ICC phenotype. Further characterisation of these cells will provide new insights into human GI biology, with the potential for developing novel therapies to address the fundamental causes of GI dysmotility.

Metastasis-associated protein 1 (MTA1) regulates the catecholamine production homeostasis via transcriptional repression of aromatic l-amino acid decarboxylase (Aadc) in the interstitial cells of Cajal of mouse prostate

Based on the lately identified role for the interstitial cells of Cajal (ICCs) of mouse prostate in catecholamine production, as well as the well-established role for the master coregulator metastasis-associated protein 1 (MTA1) in inflammation, we probed into the functional link between aberrant MTA1 expression and pathogenesis of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) using both a MTA1−/− mouse model of experimental autoimmune prostatitis (EAP) and an in vitro chronic prostatitis model in cultured murine ICCs. EAP-induced MTA1 expression was enriched in ICCs of mouse prostate. EAP resulted in a higher increase in the pelvic pain response in MTA1−/− mice compared to WT mice. Consistently, the ICCs from MTA1−/− mice produced higher levels of catecholamines upon induction of in vitro chronic prostatitis. Mechanistically, MTA1 could directly suppress the transcription of Aadc, a rate-limiting enzyme during catecholamine synthesis, in a HDAC2-depdendent manner. Importantly, treatment with AADC inhibitor NSD-1015 significantly ameliorated EAP-elicited pain response and catecholamine overactivity in MTA1−/− mice. Taken together, our findings reveal an inherent regulatory role of the MTA1/AADC pathway in the maintenance of catecholamine production homeostasis in prostate ICCs, and also point to a potential use of HDAC inhibitors and/or AADC inhibitors to treat CP/CPPS.

Nitric oxide-induced oxidative stress impairs pacemaker function of murine interstitial cells of Cajal during inflammation

The pacemaker function of interstitial cells of Cajal (ICC) is impaired during intestinal inflammation. The aim of this study is to clarify the pathophysiological mechanisms of ICC dysfunction during inflammatory condition by using intestinal cell clusters. Cell clusters were prepared from smooth muscle layer of murine jejunum and treated with interferon-gamma and lipopolysaccharide (IFN-γ+LPS) for 24h to induce inflammation. Pacemaker function of ICC was monitored by measuring cytosolic Ca2+ oscillation in the presence of nifedipine. Treatment with IFN-γ+LPS impaired the pacemaker activity of ICC with increasing mRNA level of interleukin-1 beta, tumor necrosis factor-alpha and interleukin-6 in cell clusters; however, treatment with these cytokines individually had little effect on pacemaker activity of ICC. Treatment with IFN-γ+LPS also induced the expression of inducible nitric oxide synthase (iNOS) in smooth muscle cells and resident macrophages, but not in ICC. Pretreatment with NOS inhibitor, L-NAME or iNOS inhibitor, 1400W ameliorated IFN-γ+LPS-induced pacemaker dysfunction of ICC. Pretreatment with guanylate cyclase inhibitor, ODQ did not, but antioxidant, apocynin, to suppress NO-induced oxidative stress, significantly suppressed the impairment of ICC function induced by IFN-γ+LPS. Treatment with IFN-γ+LPS also decreased c-Kit-positive ICC, which was prevented by pretreatment with L-NAME. However, apoptotic ICC were not detected in IFN-γ+LPS-treated clusters, suggesting IFN-γ+LPS stimulation just changed the phenotype of ICC but not induced cell death. Moreover, ultrastructure of ICC was not disturbed by IFN-γ+LPS. In conclusion, ICC dysfunction during inflammation is induced by NO-induced oxidative stress rather than NO/cGMP signaling. NO-induced oxidative stress might be the main factor to induce phenotypic changes of ICC.

Ginsenoside Re inhibits pacemaker potentials via adenosine triphosphate-sensitive potassium channels and the cyclic guanosine monophosphate/nitric oxide-dependent pathway in cultured interstitial cells of Cajal from mouse small intestine

BackgroundGinseng belongs to the genus Panax. Its main active ingredients are the ginsenosides. Interstitial cells of Cajal (ICCs) are the pacemaker cells of the gastrointestinal (GI) tract. To understand the effects of ginsenoside Re (GRe) on GI motility, the authors investigated its effects on the pacemaker activity of ICCs of the murine small intestine. MethodsInterstitial cells of Cajal were dissociated from mouse small intestines by enzymatic digestion. The whole-cell patch clamp configuration was used to record pacemaker potentials in cultured ICCs. Changes in cyclic guanosine monophosphate (cGMP) content induced by GRe were investigated. ResultsGinsenoside Re (20–40μM) decreased the amplitude and frequency of ICC pacemaker activity in a concentration-dependent manner. This action was blocked by guanosine 5′-[β-thio]diphosphate [a guanosine-5'-triphosphate (GTP)-binding protein inhibitor] and by glibenclamide [an adenosine triphosphate (ATP)-sensitive K+ channel blocker]. To study the GRe-induced signaling pathway in ICCs, the effects of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (a guanylate cyclase inhibitor) and RP-8-CPT-cGMPS (a protein kinase G inhibitor) were examined. Both inhibitors blocked the inhibitory effect of GRe on ICC pacemaker activity. L-NG-nitroarginine methyl ester (100μM), which is a nonselective nitric oxide synthase (NOS) inhibitor, blocked the effects of GRe on ICC pacemaker activity and GRe-stimulated cGMP production in ICCs. ConclusionIn cultured murine ICCs, GRe inhibits the pacemaker activity of ICCs via the ATP-sensitive potassium (K+) channel and the cGMP/NO-dependent pathway. Ginsenoside Re may be a basis for developing novel spasmolytic agents to prevent or alleviate GI motility dysfunction.

Quercetin Inhibits Pacemaker Potentials via Nitric Oxide/cGMP-Dependent Activation and TRPM7/ANO1 Channels in Cultured Interstitial Cells of Cajal from Mouse Small Intestine

Background: Quercetin regulates gastrointestinal (GI) motor activity but the molecular mechanism involved has not been determined. The authors investigated the effects of quercetin, a flavonoid present in various foods, on the pacemaker activities of interstitial cells of Cajal (ICCs) in murine small intestine in vitro and on GI motility in vivo. Materials and Methods: Enzymatic digestion was used to dissociate ICCs from mouse small intestines. The whole-cell patch-clamp configuration was used to record pacemaker potentials in cultured ICCs in the absence or presence of quercetin and to record membrane currents of transient receptor potential melastatin (TRPM) 7 or transmembrane protein 16A (Tmem16A, anoctamin1 (ANO1)) overexpressed in human embryonic kidney (HEK) 293 cells. The in vivo effects of quercetin on GI motility were investigated by measuring the intestinal transit rates (ITRs) of Evans blue in normal mice. Results: Quercetin (100-200 μM) decreased the amplitudes and frequencies of pacemaker activity in a concentration-dependent manner in current clamp mode, but this action was blocked by naloxone (a pan-opioid receptor antagonist) and by GDPβS (a GTP-binding protein inhibitor). However, potassium channels were not involved in these inhibitory effects of quercetin. To study the quercetin signaling pathway, we examined the effects of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of guanylate cyclase, and of RP-8-CPT-cGMPS, an inhibitor of protein kinase G (PKG). These inhibitors blocked the inhibitory effects of quercetin on pacemaker activities. Also, L-NAME (100 μM), a non-selective NO synthase (NOS) inhibitor, blocked the effects of quercetin on pacemaker activity and quercetin stimulated cGMP production. Furthermore, quercetin inhibited both Ca²⁺-activated Cl^- channels (TMEM16A, ANO1) and TRPM7 channels. In vivo, quercetin (10-100 mg/kg, p.o.) decreased ITRs in normal mice in a dose-dependent manner. Conclusions: Quercetin inhibited ICC pacemaker activities by inhibiting TRPM7 and ANO1 via opioid receptor signaling pathways in cultured murine ICCs. The study shows quercetin attenuates GI tract motility, and suggests quercetin be considered the basis for the development of novel spasmolytic agents for the prevention or alleviation of GI motility dysfunctions.

Characteristics of Gintonin-Mediated Membrane Depolarization of Pacemaker Activity in Cultured Interstitial Cells of Cajal

Background/Aims: Ginseng regulates gastrointestinal (GI) motor activity but the underlying components and molecular mechanisms are unknown. We investigated the effect of gintonin, a novel ginseng-derived G protein-coupled lysophosphatidic acid (LPA) receptor ligand, on the pacemaker activity of the interstitial cells of Cajal (ICC) in murine small intestine and GI motility. Materials and Methods: Enzymatic digestion was used to dissociate ICC from mouse small intestines. The whole-cell patch-clamp configuration was used to record pacemaker potentials and currents from cultured ICC in the absence or presence of gintonin. In vivo effects of gintonin on gastrointestinal (GI) motility were investigated by measuring the intestinal transit rate (ITR) of Evans blue in normal and streptozotocin (STZ)-induced diabetic mice. Results: We investigated the effects of gintonin on pacemaker potentials and currents in cultured ICC from mouse small intestine. Gintonin caused membrane depolarization in current clamp mode but this action was blocked by Ki16425, an LPA1/3 receptor antagonist, and by the addition of GDPβS, a GTP-binding protein inhibitor, into the ICC. To study the gintonin signaling pathway, we examined the effects of U-73122, an active PLC inhibitor, and chelerythrine and calphostin, which inhibit PKC. All inhibitors blocked gintonin actions on pacemaker potentials, but not completely. Gintonin-mediated depolarization was lower in Ca²⁺-free than in Ca²⁺-containing external solutions and was blocked by thapsigargin. We found that, in ICC, gintonin also activated Ca²⁺-activated Cl^- channels (TMEM16A, ANO1), but not TRPM7 channels. In vivo, gintonin (10-100 mg/kg, p.o.) not only significantly increased the ITR in normal mice but also ameliorated STZ-induced diabetic GI motility retardation in a dose-dependent manner. Conclusions: Gintonin-mediated membrane depolarization of pacemaker activity and ANO1 activation are coupled to the stimulation of GI contractility through LPA1/3 receptor signaling pathways in cultured murine ICC. Gintonin might be a ingredient responsible for ginseng-mediated GI tract modulations, and could be a novel candidate for development as a prokinetic agent that may prevent or alleviate GI motility dysfunctions in human patients.

Role of Calcium in Activation of Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels Caused by Cholecystokinin Octapeptide in Interstitial Cells of Cajal

Background: Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels regulate pacemaker activity in some cardiac cells and neurons. Little is known about the effects of cholecystokinin octapeptide (CCK-8) on HCN channels and excitability of murine interstitial cells of Cajal (ICCs). Methods: In the present study, the effects and mechanisms of CCK-8 on HCN channels were investigated by measuring mechanical contraction of smooth muscle strips and ionic channels of ICCs in murine gastric antrum. Results: Sulfated CCK-8 (CCK-8S) was used, and we found that CCK-8S increased the contraction of smooth muscle strips in the gastric antrum, which could be suppressed by specific HCN channel blockers CsCl and ZD7288. Extracellular calcium could also intensify the contraction. Under the same conditions, when antral strips were exposed to calcium ion (Ca²⁺)-free solution, no significant changes could be recorded with CCK-8S or ZD7288. Isolated ICCs from the murine gastric antrum identified by specific c-Kit antibody primers were chosen for electrophysiological recordings. HCN current (I_h) of cultured ICCs was studied by whole-cell patch clamp techniques. A spontaneous transient inward current was recorded in ICCs, which could be inhibited by addition of CsCl and ZD7288; the current proved to be I_h. CCK-8S-facilitated I_h in cultured ICCs could be inhibited by CsCl and ZD7288. When cultured ICCs were exposed to Ca²⁺-free solution, no significant changes could be recorded by application of CCK-8S on I_h, which proved extracellular calcium might have an excitatory effect on HCN channels. Conclusion: We demonstrate that HCN channels are present in ICCs in the murine gastric antrum; they might be an important regulator of ICC excitability and pacemaker activity and are strongly affected by CCK-8S. Extracellular calcium might be a trigger in the activation of HCN channels caused by CCK-8S in cultured ICCs.

275 Adult Stem Cells for Murine Interstitial Cells of Cajal (ICC) Mediate Immunosuppression In Vitro

275 Adult Stem Cells for Murine Interstitial Cells of Cajal (ICC) Mediate Immunosuppression In Vitro

Differential expression of neural markers in KIT and PDGFRA wild-type gastrointestinal stromal tumours

To compare the genomic signatures of wild-type (WT) and mutated GISTs and the murine interstitial cells of Cajal (ICCs) to find markers of cell differentiation and other functions that may identify cells that give rise to WT tumours. We analysed the gene expression profiles of a total of 30 tumour samples (four WT GISTs and 26 mutated GISTs), selected the genes most differentially expressed (P < 0.001:448 probe sets) and validated these results by quantitative polymerase chain reaction (PCR) and immunohistochemistry. In addition, we conducted a meta-analysis merging data from human GISTs with a genomic data set from murine ICCs. The gene expression profiles of WT and mutated GISTs differed profoundly, especially in the expression of those genes restricted primarily to neural tissues. We found that mature ICCs are more similar to mutated GISTs than WT GISTs. WT GISTs have different genomic profiles from both mutated GISTs and murine mature ICCs. Considering that IGF1R expression is common to both WT GISTs and putative precursor ICCs, this study suggests that WT GISTs may derive either from ICCs at a different step of differentiation or from a different cell of origin.

Characterization of depolarization‐evoked ERG K+ currents in interstitial cells of Cajal

Interstitial cells of Cajal (ICC) harbour the ether-a-go-go related gene (ERG) channel as shown by its characteristic rapidly deactivating current upon hyperpolarization. This property, however, does not explain the marked increase in cell excitability by ERG channel blockers, namely an increase in slow wave plateau duration and action potential generation. The objective of the present study was to characterize the depolarization-activated, E4031-sensitive ERG currents in murine ICC within a range of physiologically relevant membrane potentials. Whole cell currents were recorded from ICC isolated from murine neonatal jejunum, superfused with a physiological salt solution and with high intracellular Cs(+) to block most other K(+) currents. Upon depolarizing the cell from the resting membrane potential (approximately -60 mV) towards the region of the slow wave plateau (approximately -30 mV), significant sustained (window) current was generated between the potentials of -40 to 0 mV (maximal at -30 mV) and inhibited by the ERG specific blocker E4031. Channel activation followed by rapid inactivation produced a steady state conductance at -30 mV which was 51.6 +/- 11% of the hyperpolarization-evoked peak conductance value at -100 mV. When the cell repolarized from -30 mV, again, significant currents were generated, indicating recovery from inactivation, a typical characteristic of ERG channels. These data provide evidence that the ERG channel is of significance in the regulation of ICC excitability and provide the mechanism by which ERG channel blockade increases the slow wave duration.

Quantitative analysis by flow cytometry of interstitial cells of Cajal, pacemakers, and mediators of neurotransmission in the gastrointestinal tract

Interstitial cells of Cajal (ICCs) are mesenchymal cells that play critical roles in gastrointestinal motility as electrical pacemakers and mediators of neuromuscular neurotransmission. Although depletions of ICCs have been implicated in several gastrointestinal motor disorders, quantification of these cells has been difficult due to their varied morphology, regionally changing network density, and overall scarcity. Our goal was to evaluate flow cytometry (FCM) for the enumeration of ICCs. We identified murine ICCs in live gastrointestinal muscles or primary cell cultures grown in the presence or absence of stem cell factor (SCF)-expressing STO fibroblasts with fluorescent Kit (CD117) antibodies. Because this technique also labels resident macrophages nonspecifically, we identified the latter with additional fluorescent antibodies. Dispersed cells were analyzed by FCM. ICCs represented 1.63 +/- 0.17% of the total cell count in the distal stomach (n = 18 mice) and 5.85 +/- 0.84% in the proximal colon and 6.28 +/- 0.61% in the distal colon (n = 3 mice). In fundic muscles of W/WV mice (n = 5) that virtually lack ICCs, very few Kit+ cells were detected. FCM identified approximately 2.6- to 7.3-fold more Kit+ ICCs in small intestinal cell cultures grown on STO fibroblasts expressing membrane-bound SCF (n = 6) than in cultures stimulated with soluble SCF (n = 6). FCM is a sensitive and specific method for the unbiased quantification of ICCs.

Purification of interstitial cells of Cajal by fluorescence-activated cell sorting.

Interstitial cells of Cajal (ICC) in the gastrointestinal tract generate and propagate slow waves and mediate neuromuscular neurotransmission. Although damages to ICC have been described in several gastrointestinal motor disorders, analysis of their gene expression in health and disease has been problematic because of the difficulties in isolating these cells. Our goal was to develop techniques for large-scale purification of ICC. Murine ICC were identified in live gastrointestinal muscles with fluorescent Kit antibodies. Because this technique also labels resident macrophages nonspecifically, we attempted to separate ICC from these cells by fluorescence-activated cell sorting with or without immunomagnetic presorting. Efficacy and specificity of ICC purification were tested by quantitative RT-PCR of cell-specific markers. Fluorescence-based separation of small intestinal ICC from unlabeled cells and macrophages tagged with F4/80 antibodies yielded 30,000-40,000 cells and approximately 60-fold enrichment of c-kit mRNA. However, the macrophage marker CD68 was also enriched approximately 6-fold. Magnetic presorting of ICC did not significantly improve selectivity. After labeling contaminating cells with additional paramagnetic (anti-CD11b, -CD11c) and fluorescent antibodies (anti-CD11b) and depleting them by magnetic presorting, we harvested approximately 2,000-4,000 cells from single gastric corpus-antrum muscles and detected an approximately 30-fold increase in c-kit mRNA, no enrichment of mast cells, and an approximately 4-fold reduction of CD68 expression. Adding labeled anti-CD45 antibody to our cocktail further increased c-kit enrichment and eliminated mast cells and macrophages. Smooth muscle cells and myenteric neurons were also depleted. We conclude that immunofluorescence-based sorting can yield ICC in sufficiently high numbers and purity to permit detailed molecular analyses.

A Ca2+‐inhibited non‐selective cation conductance contributes to pacemaker currents in mouse interstitial cell of Cajal

Interstitial cells of Cajal (ICC) provide pacemaker activity in some smooth muscles. The nature of the pacemaker conductance is unclear, but studies suggest that pacemaker activity is due to a voltage-independent, Ca(2+)-regulated, non-selective cation conductance. We investigated Ca(2+)-regulated conductances in murine intestinal ICC and found that reducing cytoplasmic Ca(2+) activates whole-cell inward currents and single-channel currents. Both the whole-cell currents and single-channel currents reversed at 0 mV when the equilibrium potentials of all ions present were far from 0 mV. Recordings from on-cell patches revealed oscillations in unitary currents at the frequency of pacemaker currents in ICC. Voltage-clamping cells to -60 mV did not change the oscillatory activity of channels in on-cell patches. Depolarizing cells with high external K(+) caused loss of resolvable single-channel currents, but the oscillatory single-channel currents were restored when the patches were stepped to negative potentials. Unitary currents were also resolved in excised patches. The single-channel conductance was 13 pS, and currents reversed at 0 mV. The channels responsible were strongly activated by 10(-7) M Ca(2+), and 10(-6) M Ca(2+) reduced activity. The 13 pS channels were strongly activated by the calmodulin inhibitors calmidazolium and W-7 in on-cell and excised patches. Calmidazolium and W-7 also activated a persistent inward current under whole-cell conditions. Murine ICC express Ca(2+)-inhibited, non-selective cation channels that are periodically activated at the same frequency as pacemaker currents. This conductance may contribute to the pacemaker current and generation of electrical slow waves in GI muscles.

Dose-dependent and time-limited proliferation of cultured murine interstitial cells of Cajal in response to stem cell factor

Interstitial cells of Cajal (ICCs) play a role as pacemakers for gastrointestinal movement. Although some in vivo experiments showed that the c- kit receptor tyrosine kinase (KIT) and its ligand, stem cell factor (SCF), might be required for the development of murine ICCs near birth, in vitro experiments would be useful to clarify the role of SCF-KIT system for the development of ICCs. We attempted to establish a culture system in order to investigate the proliferation of ICCs. Murine gastrointestinal cells from embryos or neonates were cultured with SCF and stained with anti-KIT antibody and/or alcian-blue. The numbers of KIT + cells and alcian-blue + cells were counted, and the number of KIT +·alcian-blue − cells, which represent ICCs was calculated. Clusters containing KIT + cells were formed in culture. The number of KIT +·alcian-blue − cells from day-18 post coitum embryos increased in response to SCF up to a concentration of 50 ng/ml or for 8 days. The number of cells from day-2 post-partum neonates increased for 4 days, and then remained constant in the presence of SCF. In contrast, the number of cells from day-6 post-partum neonates did not increase and remained constant, even in the presence of SCF. ICCs showed a dose-dependent and time-limited proliferation in response to SCF in the in vitro culture system used here in.

A Ca2+-inhibited non-selective cation conductance contributes to pacemaker currents in mouse interstitial cell of Cajal

Interstitial cells of Cajal (ICC) provide pacemaker activity in some smooth muscles. The nature of the pacemaker conductance is unclear, but studies suggest that pacemaker activity is due to a voltage-independent, Ca2+-regulated, non-selective cation conductance. We investigated Ca2+-regulated conductances in murine intestinal ICC and found that reducing cytoplasmic Ca2+ activates whole-cell inward currents and single-channel currents. Both the whole-cell currents and single-channel currents reversed at 0 mV when the equilibrium potentials of all ions present were far from 0 mV. Recordings from on-cell patches revealed oscillations in unitary currents at the frequency of pacemaker currents in ICC. Voltage-clamping cells to −60 mV did not change the oscillatory activity of channels in on-cell patches. Depolarizing cells with high external K+ caused loss of resolvable single-channel currents, but the oscillatory single-channel currents were restored when the patches were stepped to negative potentials. Unitary currents were also resolved in excised patches. The single-channel conductance was 13 pS, and currents reversed at 0 mV. The channels responsible were strongly activated by 10−7m Ca2+, and 10−6m Ca2+ reduced activity. The 13 pS channels were strongly activated by the calmodulin inhibitors calmidazolium and W-7 in on-cell and excised patches. Calmidazolium and W-7 also activated a persistent inward current under whole-cell conditions. Murine ICC express Ca2+-inhibited, non-selective cation channels that are periodically activated at the same frequency as pacemaker currents. This conductance may contribute to the pacemaker current and generation of electrical slow waves in GI muscles.