Pacemaker Potentials Research Articles

Commonality and heterogeneity of pacemaker mechanisms in the male reproductive organs.

During emission, the first phase of ejaculation, smooth muscle in organs of the male reproductive tract (MRT) vigorously contract upon sympathetic nerve excitation to expel semen consisting of sperm and seminal plasma. During inter-ejaculation phases, the epididymis, seminal vesicles and prostate undergo spontaneous phasic contractions (SPCs), this transporting and maintaining the quality of sperm and seminal plasma. Recent studies have revealed platelet-derived growth factor receptor α-expressing (PDGFRα+) subepithelial interstitial cells in seminal vesicles subserve the role of pacemaker cells that electrically drive SPCs in this organ. PDGFRα+ smooth muscle cells in the epididymis also appear to function as pacemaker cells implicating PDGFRα as a potential signature molecule in MRT pacemaking. The dominant mechanism driving pacemaking in these organs is the cytosolic Ca2+ oscillator. This operates through entrainment of the release-refill cycle of Ca2+ stores, the released Ca2+ ions opening Ca2+-activated chloride channels, including in some cases ANO1 (TMEM16A), with the resultant pacemaker potential activating L-type voltage-dependent Ca2+ channels in the smooth muscle causing contraction (viz. SPCs). A second pacemaker mechanism, namely the membrane oscillator also has a role in specific cases. Further investigations into the commonality and heterogeneity of MRT pacemakers will open an avenue for understanding the pathogenesis of male infertility associated with deterioration of seminal plasma.

Effect of adenosine-1 receptor activation on pacemaker activity of interstitial cells of Cajal from mouse colon.

Adenosine plays an important role on gastrointestinal (GI) motility through adenosine receptors. Interstitial cells of Cajal (ICC) are pacemaker cells that regulate GI smooth muscle activity. The functional role and its signal mechanism of adenosine on the pacemaker activity were investigated using whole-cell patch clamp, RT-PCR, and intracellular Ca2+-imaging with ICC from mouse colon. Adenosine depolarized the membrane potentials and increased the pacemaker potential frequency, which was blocked by a selective A1-receptor antagonist, but not A2a-, A2b, or A3-receptor antagonist. A selective A1 receptor agonist represented similar effects as those of adenosine and mRNA transcript of A1-receptor was expressed in ICC. The adenosine-induced effects were blocked by phospholipase C (PLC) and a Ca2+-ATPase inhibitor. Adenosine increased spontaneous intracellular Ca2+ oscillations, as seen fluo4/AM. Both hyperpolarization-activated cyclic nucleotide (HCN) channel inhibitors and adenylate cyclase inhibitors blocked the adenosine-induced effects. And adenosine increased the basal cellular adenylate cyclase activity in colonic ICC. However, adenosine and adenylate cyclase inhibitors did not show any influence on pacemaker activity in small intestinal ICC for a comparison with that of the small intestine. These results suggest adenosine modulates the pacemaker potentials by acting HCN channels- and intracellular Ca2+- dependent mechanisms through A1-receptor. Therefore, adenosine may be a therapeutic target in colonic motility disorders.

A Study on the Effects of Muscarinic and Serotonergic Regulation by Bojanggunbi-tang on the Pacemaker Potential of the Interstitial Cells of Cajal in the Murine Small Intestine.

In traditional Korean medicine, the 16-herb concoction Bojanggunbi-tang (BGT) is used to treat various gastrointestinal (GI) diseases. In this study, we investigated the regulatory mechanism underlying the influence of BGT on the interstitial cells of Cajal (ICCs), pacemaker cells in the GI tract. Within 12 h of culturing ICCs in the small intestines of mice, the pacemaker potential of ICCs was recorded through an electrophysiological method. An increase in the BGT concentration induced depolarization and decreased firing frequency. This reaction was suppressed by cholinergic receptor muscarinic 3 (CHRM3) antagonists, as well as 5-hydroxytryptamine receptor (5HTR) 3 and 4 antagonists. Nonselective cation channel inhibitors, such as thapsigargin and flufenamic acid, along with protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) inhibitors, also suppressed the BGT reaction. Guanylate cyclase and protein kinase G (PKG) antagonists inhibited BGT, but adenylate cyclase and protein kinase A antagonists had no effect. In conclusion, we demonstrated that BGT acts through CHRM3, 5HTR3, and 5HTR4 to regulate intracellular Ca2+ concentrations and the PKC, MAPK, guanylate cycle, and PKG signaling pathways.

Regional differences of tachykinin effects on smooth muscle and pacemaker potentials of the stomach, duodenum, ileum and colon of an emetic model, the house musk shrews

Background and aimsThe contractile effects of tachykinins on the gastrointestinal tract are well-known, but how they modulate slow-waves, particularly in species capable of emesis, remains largely unknown. We aimed to elucidate the effects of tachykinins on myoelectric and contractile activity of isolated gastrointestinal tissues of the Suncus murinus. MethodsThe effects of substance P (SP), neurokinin (NK)A, NKB and selective NK1 (CP122,721, CP99,994), NK2 (SR48,968, GR159,897) and NK3 (SB218,795, SB222,200) receptor antagonists on isolated stomach, duodenum, ileum and colon segments were studied. Mechanical contractile activity was recorded using isometric force displacement transducers. Electrical pacemaker activity was recorded using a microelectrode array. ResultsCompared with NKA, SP induced larger contractions in stomach tissue and smaller contractions in intestinal segments, where oscillation magnitudes increased in intestinal segments, but not the stomach. CP122,721 and GR159,897 inhibited electrical field stimulation-induced contractions of the stomach, ileum and colon. NKB and NK3 had minor effects on contractile activity. The inhibitory potencies of SP and NKA on the peristaltic frequency of the colon and ileum, respectively, were correlated with those on electrical pacemaker frequency. SP, NKA and NKB inhibited pacemaker activity of the duodenum and ileum, but increased that of the stomach and colon. SP elicited a dose-dependent contradictive pacemaker frequency response in the colon. ConclusionThis study revealed distinct effects of tachykinins on the mechanical and electrical properties of the stomach and colon vs. the proximal intestine, providing a unique aspect on neuromuscular correlation in terms of the effects of tachykinin on peristaltic and pacemaker activity in gastrointestinal-related symptoms.

Protein Kinase C Regulates Expression and Function of the Cav3.2 T-Type Ca2+ Channel during Maturation of Neonatal Rat Cardiomyocyte.

Two distinct isoforms of the T-type Ca2+ channel, Cav3.1 and Cav3.2, play a pivotal role in the generation of pacemaker potentials in nodal cells in the heart, although the isoform switches from Cav3.2 to Cav3.1 during the early neonatal period with an unknown mechanism. The present study was designed to investigate the molecular system of the parts that are responsible for the changes of T-type Ca2+ channel isoforms in neonatal cardiomyocytes using the whole-cell patch-clamp technique and mRNA quantification. The present study demonstrates that PKC activation accelerates the Ni2+-sensitive beating rate and upregulates the Ni2+-sensitive T-type Ca2+ channel current in neonatal cardiomyocytes as a long-term effect, whereas PKC inhibition delays the Ni2+-sensitive beating rate and downregulates the Ni2+-sensitive T-type Ca2+ channel current. Because the Ni2+-sensitive T-type Ca2+ channel current is largely composed of the Cav3.2-T-type Ca2+ channel, it is accordingly assumed that PKC activity plays a crucial role in the maintenance of the Cav3.2 channel. The expression of Cav3.2 mRNA was highly positively correlated with PKC activity. The expression of a transcription factor Nkx2.5 mRNA, possibly corresponding to the Cav3.2 channel gene, was decreased by an inhibition of PKCβII. These results suggest that PKC activation, presumably by PKCβII, is responsible for the upregulation of CaV3.2 T-type Ca2+ channel expression that interacts with a cardiac-specific transcription factor, Nkx2.5, in neonatal cardiomyocytes.

Two HCN4 Channels Play Functional Roles in the Zebrafish Heart.

The HCN4 channel is essential for heart rate regulation in vertebrates by generating pacemaker potentials in the sinoatrial node. HCN4 channel abnormality may cause bradycardia and sick sinus syndrome, making it an important target for clinical research and drug discovery. The zebrafish is a popular animal model for cardiovascular research. They are potentially suitable for studying inherited heart diseases, including cardiac arrhythmia. However, it has not been determined how similar the ion channels that underlie cardiac automaticity are in zebrafish and humans. In the case of HCN4, humans have one gene, whereas zebrafish have two ortholog genes (DrHCN4 and DrHCN4L; ‘Dr’ referring to Danio rerio). However, it is not known whether the two HCN4 channels have different physiological functions and roles in heart rate regulation. In this study, we characterized the biophysical properties of the two zebrafish HCN4 channels in Xenopus oocytes and compared them to those of the human HCN4 channel. We found that they showed different gating properties: DrHCN4L currents showed faster activation kinetics and a more positively shifted G-V curve than did DrHCN4 and human HCN4 currents. We made chimeric channels of DrHCN4 and DrHCN4L and found that cytoplasmic domains were determinants for the faster activation and the positively shifted G-V relationship in DrHCN4L. The use of a dominant-negative HCN4 mutant confirmed that DrHCN4 and DrHCN4L can form a heteromultimeric channel in Xenopus oocytes. Next, we confirmed that both are sensitive to common HCN channel inhibitors/blockers including Cs+, ivabradine, and ZD7288. These HCN inhibitors successfully lowered zebrafish heart rate during early embryonic stages. Finally, we knocked down the HCN4 genes using antisense morpholino and found that knocking down either or both of the HCN4 channels caused a temporal decrease in heart rate and tended to cause pericardial edema. These findings suggest that both DrHCN4 and DrHCN4L play a significant role in zebrafish heart rate regulation.

Prediction of the Medicinal Mechanisms of Pinellia ternata Breitenbach, a Traditional Medicine for Gastrointestinal Motility Disorders, through Network Pharmacology.

Pinellia ternata Breitenbach (PTB) is a widely used herbal medicine in China, Japan, and South Korea. It has antiemetic, anti-inflammatory, antitussive, and sedative properties. The raw material is toxic, but can be made safer using alum solution or by boiling it for a long time. In addition, PTB seems to be effective for gastrointestinal motility disorders (GMDs), but this is yet to be conclusively proven. Herein, PTB compounds, targets, and related diseases were investigated using the traditional Chinese medical systems pharmacology database and an analysis platform. Information on target genes was confirmed using the UniProt database. Using Cytoscape 3.8.2, a network was established and GMD-related genes were searched using the Cytoscape stringApp. The effects of the PTB extract on the pacemaker potential of interstitial cells of Cajal and GMD mouse models were investigated. In total, 12 compounds were found to target 13 GMD-related genes. In animal experiments, PTB was found to better regulate pacemaker potential in vitro and inhibit GMD signs compared to control groups in vivo. Animal studies showed that the mechanism underlying the effects of PTB is closely related to gastrointestinal motility. The results obtained demonstrated that PTB offers a potential means to treat GMDs, and we suggested that the medicinal mechanism of GMDs can be explained by the relationship between 12 major components of PTB, including oleic acid, and 13 GMD-related genes.

Trypsin Depolarizes Pacemaker Potentials in Murine Small Intestinal Interstitial Cells of Cajal

Interstitial cells of Cajal (ICCs) generate pacemaker potentials in the gastrointestinal (GI) tract. In this study, the effects of trypsin on pacemaker potentials in murine small intestinal ICCs were examined. We used whole-cell patch-clamp analysis. The results of whole-cell patch-clamp analysis revealed that trypsin dose-dependently depolarized pacemaker potentials and decreased their amplitude. Treatments with the antagonists of neurokinin1 (NK1) and NK2 receptors (SR-140333 and SR-48968, respectively) slightly inhibited the trypsin-induced responses. However, treatment with the combination of SR-140333 and SR-48968 completely inhibited trypsin-induced responses. Trypsin slightly depolarized pacemaker potentials and increased their amplitude after the intracellular application of GDP-β-S. Additionally, incubation in external Ca2+-free solution inhibited trypsin-induced responses. In the presence of U-73122, staurosporine, Go6976, or xestospongin C, trypsin did not depolarize the pacemaker’s potentials. However, trypsin depolarized the pacemaker potentials in the presence of rottlerin. Finally, HC067047, a TRPV4 inhibitor, did not affect the trypsin-induced responses. These results suggest that trypsin depolarized pacemaker potentials through NK1 and NK2 receptors in the murine small intestinal ICCs, with this effect being dependent on the G protein, phospholipase C, protein kinase C, inositol triphosphate pathways, and extracellular Ca2+ but being independent of the TRPV4 pathway. Hence, trypsin-mediated GI motility regulation must be considered for prokinetic drug developments.

Inhibitory Effects of Jakyakgamcho-Tang (Glycyrrhiza uralensis and Paeonia lactiflora) on the Pacemaker Potential of the Interstitial Cells of Cajal in the Murine Small Intestine

Jakyakgamcho-tang (JYGCT) has been used to treat various diseases. The interstitial cells of Cajal (ICC) regulate gastrointestinal (GI) motility as pacemaker cells. Here, we examined the effects of JYGCT on the pacemaker potential of the ICC in the small intestine. We observed that JYGCT inhibited the pacemaker potential in a dose-dependent manner. Glibenclamide did not affect the pacemaker potential and on these conditions, JYGCT also had no effect on the pacemaker potential. Pretreatment with capsazepine or SB452533 blocked the JYGCT-induced effects. In the presence of SQ-22536, JYGCT did not inhibit the pacemaker potential. Additionally, JYGCT inhibited spontaneous [Ca2+]i oscillations and JYGCT-induced ITR increase was associated with TMEM16A, motilin and substance P activation. Moreover, JYGCT was effective in alleviating the symptoms of irritable bowel syndrome. Our results suggest that JYGCT inhibited the pacemaker potential of the ICC via KATP, the TRPV1 or the cyclic AMP pathway, and intracellular Ca2+ regulation, indicating that JYGCT can affect ICC and thus have the function of regulating GI motility. Therefore, JYGCT may be used as a GI motility disorder regulator or disease prevention agent.

Frequency-Dependent Properties of the Hyperpolarization-Activated Cation Current, If, in Adult Mouse Heart Primary Pacemaker Myocytes.

A number of distinct electrophysiological mechanisms that modulate the myogenic spontaneous pacemaker activity in the sinoatrial node (SAN) of the mammalian heart have been investigated extensively. There is agreement that several (3 or 4) different transmembrane ionic current changes (referred to as the voltage clock) are involved; and that the resulting net current interacts with direct and indirect effects of changes in intracellular Ca2+ (the calcium clock). However, significant uncertainties, and important knowledge gaps, remain concerning the functional roles in SAN spontaneous pacing of many of the individual ion channel- or exchanger-mediated transmembrane current changes. We report results from patch clamp studies and mathematical modeling of the hyperpolarization-activated current, If, in the generation/modulation of the diastolic depolarization, or pacemaker potential, produced by individual myocytes that were enzymatically isolated from the adult mouse sinoatrial node (SAN). Amphotericin-mediated patch microelectrode recordings at 35 °C were made under control conditions and in the presence of 5 or 10 nM isoproterenol (ISO). These sets of results were complemented and integrated with mathematical modeling of the current changes that take place in the range of membrane potentials (−70 to −50 mV), which corresponds to the ‘pacemaker depolarization’ in the adult mouse SAN. Our results reveal a very small, but functionally important, approximately steady-state or time-independent current generated by residual activation of If channels that are expressed in these pacemaker myocytes. Recordings of the pacemaker depolarization and action potential, combined with measurements of changes in If, and the well-known increases in the L-type Ca2+ current, ICaL, demonstrated that ICaL activation, is essential for myogenic pacing. Moreover, after being enhanced (approximately 3-fold) by 5 or 10 nM ISO, ICaL contributes significantly to the positive chronotropic effect. Our mathematical model has been developed in an attempt to better understand the underlying mechanisms for the pacemaker depolarization and action potential in adult mouse SAN myocytes. After being updated with our new experimental data describing If, our simulations reveal a novel functional component of If in adult mouse SAN. Computational work carried out with this model also confirms that in the presence of ISO the residual activation of If and opening of ICaL channels combine to generate a net current change during the slow diastolic depolarization phase that is essential for the observed accelerated pacemaking rate of these SAN myocytes.

Effects of black garlic on the pacemaker potentials of interstitial cells of Cajal in murine small intestine in vitro and on gastrointestinal motility in vivo

ABSTRACT Black garlic (BG) is a newly explored food stuff obtained via fermentation of raw, healthy garlic, especially in Asian countries. Interstitial cells of Cajal (ICC) are the pacemaker cells of gastrointestinal (GI) motility. The purpose of this study was to investigate the effects of BG extract on the pacemaker potentials of the ICC in the small intestines of mice and the possibility of controlling GI motility. The antioxidant activity of BG extract was also investigated. The whole-cell electrophysiological method was used to measure pacemaker potentials of the ICC in vitro, whereas GI motility was measured using the intestinal transit rate (ITR) in vivo. BG extract depolarized the pacemaker potentials of the ICC. Y25130 and RS39604 5-HT receptor antagonists could not inhibit the effect of BG extract on the pacemaker potentials of the ICC, whereas the 5-HT receptor antagonist SB269970 could. Pre-treatment with external Na+ (5 mM) or Ca2+-free solution inhibited the BG extract-induced depolarization of the ICC. With SB203580, PD98059, or c-jun NH2-terminal kinase II inhibitor pre-treatment, BG extract did not induce pacemaker potential depolarization. Moreover, the ITR values were increased by BG extract. Elevation of the ITR due to BG extract was related with increased protein expression of the 5-HT7 receptors. In addition, BG extract showed antioxidant activity. Collectively, these results highlight the ability of BG extract to regulate GI motility and the possibility of using it to develop GI motility modulators in the future. Moreover, BG showed immense potential as an antioxidant.

Grape seed powder increases gastrointestinal motility.

Grape seed is an important natural bioactive product with various health benefits. Interstitial cells of Cajal (ICCs) are pacemaker cells in the gastrointestinal (GI) tract. The present study investigated the effects of grape seed powder (GSP) on ICC properties and GI motility. GSP depolarized the pacemaker potentials of ICCs in a dose‑dependent manner. Y25130 or SB269970 slightly inhibited GSP‑induced effects. However, Y25130 and SB269970 together completely blocked GSP-induced effects. In the presence of inhibitors of protein kinase C, protein kinase A, or mitogen-activated protein kinase, GSP‑induced ICC depolarization was inhibited. GSP increased the intestinal transit rate in normal mice and in mice with acetic acid-induced GI motility disorder. In addition, the levels of motilin and substance P were elevated after GSP dosing. These results demonstrate that GSP can regulate GI motility, and therefore, it is a potential therapeutic agent for treating GI motility disorders.

Hyperpolarization-activated cyclic nucleotide-gated channels working as pacemaker channels in colonic interstitial cells of Cajal.

Hyperpolarization‐activated cyclic nucleotide‐gated (HCN) channels function as pacemaker channels in spontaneously active cells. We studied the existence of HCN channels and their functional roles in the interstitial cells of Cajal (ICC) from the mouse colon using electrophysiological, immunohistochemical and molecular techniques. HCN1 and HCN3 channels were detected in anoctamin‐1 (Ca2+‐activated Cl− channel; ANO1)‐positive cells within the muscular and myenteric layers in colonic tissues. The mRNA transcripts of HCN1 and HCN3 channels were expressed in ANO1‐positive ICC. In the deletion of HCN1 and HCN3 channels in colonic ICC, the pacemaking potential frequency was reduced. Basal cellular adenylate cyclase activity was decreased by adenylate cyclase inhibitor in colonic ICC, whereas cAMP‐specific phosphodiesterase inhibitors increased it. 8‐Bromo‐cyclic AMP and rolipram increased spontaneous intracellular Ca2+ oscillations. In addition, Ca2+‐dependent adenylate cyclase 1 (AC1) mRNA was detected in colonic ICC. Sulprostone, a PGE2‐EP3 agonist, increased the pacemaking potential frequency, maximum rate of rise of resting membrane in pacemaker potentials and basal cellular adenylate cyclase activity in colonic ICC. These results indicate that HCN channels exist in colonic ICC and participate in generating pacemaking potentials. Thus, HCN channels may be therapeutic targets in disturbed colonic motility disorders.

Interstitial Cells of Cajal: Potential Targets for Functional Dyspepsia Treatment Using Medicinal Natural Products.

Introduction The pathophysiology of functional dyspepsia (FD) remains uncertain, but the interstitial cells of Cajal (ICCs), pacemakers that regulate gastrointestinal motility, are garnering attention as key modulators and therapeutic targets in FD. This review comprehensively discusses the involvement of ICCs in the pharmacologic actions of FD and as therapeutic targets for herbal products for FD. Methods A search of the literature was performed using PubMed by pairing “interstitial cells of Cajal” with “medicinal plant, herbal medicine, phytotherapy, flavonoids, or traditional Chinese medicine (TCM).” Results From the 55 articles screened in the initial survey, 34 articles met our study criteria. The search results showed that herbal products can directly depolarize ICCs to generate pacemaker potentials and increase the expression of c-kit and stem cell factors, helping to repair ICCs. Under certain pathological conditions, medicinal plants also protect ICCs from oxidative stress and/or inflammation-induced impairment. Two representative herbal decoctions (Banhasasim-tang, 半夏泻心汤, and Yukgunja-tang, 六君子汤) have been shown to modulate ICC functions by both clinical and preclinical data. Conclusion This review strongly indicates the potential of herbal products to target ICCs and suggests that further ICC-based studies would be promising for the development of FD treatment agents.

Electrophysiological Effects of Ionophore-induced Increases in Intracellular Na+ in Cardiomyocytes

Na ionophores increase intracellular Na+ ([Na+]i). Membrane potentials and currents were measured using microelectrode and whole-cell patch-clamp techniques. Monensin (10-6-3×10-5 M) reduced the slope of the pacemaker potentials and shortened the action potential duration (APD) in sino-atrial nodal and Purkinje cells. Monensin (10-5 M) shortened the APD and reduced the amplitude of the plateau phase in ventricular myocytes. Monensin decreased the hyperpolarization-activated inward current (If), and it increased the transient outward potassium current (Ito) in Purkinje cells. In addition, monensin decreased the sodium current (INa), shifting the inactivation curve to the hyperpolarized direction. Moreover, monensin decreased the L-type calcium current (ICa) in ventricular myocytes. The Na+-Ca2+ exchange current (INa-Ca) was augmented particularly in the reverse mode, and the Na+-K+ pump current (INa-K) was also activated by monensin in cardiomyocytes. The ATP-activated potassium current (IK,ATP) could be induced by monensin. Notably, the inward rectifying K+ current (IK1), and the slow delayed outward K+ current (IKs) were not affected evidently by monensin. Collectively, alteration of [Na+]i can influence the activities of various ion channels and transporters. Thus, the significance of altered [Na+]i should be taken into consideration in the action of drugs affecting [Na+]i such as digitalis, Na+ channel blockers, and Na+ channel activating agents.

Involvement of TRPV1 and TRPA1 in the modulation of pacemaker potentials in the mouse ileum

BackgroundThe roles of transient receptor potential cation channel, subfamily V, member 1 (TRPV1) and subfamily A, member 1 (TRPA1) in mechanisms of gastrointestinal motility are complex. This study aimed to clarify the effects of several TRPV1 and TRPA1 ligands on the electrical potentials generated by pacemaker cells in the mouse-isolated ileum. MethodThe pacemaker potentials of ileal segments of mice were recorded extracellularly using a 60-channel microelectrode array. The dominant frequencies, average waveform periods and propagation velocities were quantified. The effects of TRPV1 and TRPA1 agonist and antagonist were compared with the baseline recordings. ResultsThe electrophysiological recordings showed that capsaicin (30 μM to 3 mM), resiniferatoxin (300 μM), capsazepine (100–300 μM), allyl isothiocyanate (300 μM), isovelleral (300 μM), icilin (300 μM), A-967,079 (10 μM), AP18 (20 μM) and HC-030,031 (50 μM) significantly reduced the pacemaker frequency and increased the waveform period relative to the baseline. Conversely, ruthenium red (300 μM) significantly increased the pacemaker frequency and reduced the waveform period. Capsaicin (3 mM) and AP18 (20 μM) also significantly reduced the propagation velocity. However, all tested antagonists failed to inhibit the effects of agonists. AMG9810 (300 μM), but not A-967,079 (300 μM), significantly inhibited the increases in pacemaker frequency caused by increased temperatures. ConclusionOur findings suggest that TRPV1 and TRPA1 play a minor role in regulating pacemaker potentials and that at non-specific actions at other TRP and ion channels most likely contributed to the overall effects on the electrophysiological recordings that we observed.

Physiological Roles of the Rapidly Activated Delayed Rectifier K+ Current in Adult Mouse Heart Primary Pacemaker Activity.

Robust, spontaneous pacemaker activity originating in the sinoatrial node (SAN) of the heart is essential for cardiovascular function. Anatomical, electrophysiological, and molecular methods as well as mathematical modeling approaches have quite thoroughly characterized the transmembrane fluxes of Na+, K+ and Ca2+ that produce SAN action potentials (AP) and ‘pacemaker depolarizations’ in a number of different in vitro adult mammalian heart preparations. Possible ionic mechanisms that are responsible for SAN primary pacemaker activity are described in terms of: (i) a Ca2+-regulated mechanism based on a requirement for phasic release of Ca2+ from intracellular stores and activation of an inward current-mediated by Na+/Ca2+ exchange; (ii) time- and voltage-dependent activation of Na+ or Ca2+ currents, as well as a cyclic nucleotide-activated current, If; and/or (iii) a combination of (i) and (ii). Electrophysiological studies of single spontaneously active SAN myocytes in both adult mouse and rabbit hearts consistently reveal significant expression of a rapidly activating time- and voltage-dependent K+ current, often denoted IKr, that is selectively expressed in the leading or primary pacemaker region of the adult mouse SAN. The main goal of the present study was to examine by combined experimental and simulation approaches the functional or physiological roles of this K+ current in the pacemaker activity. Our patch clamp data of mouse SAN myocytes on the effects of a pharmacological blocker, E4031, revealed that a rapidly activating K+ current is essential for action potential (AP) repolarization, and its deactivation during the pacemaker potential contributes a small but significant component to the pacemaker depolarization. Mathematical simulations using a murine SAN AP model confirm that well known biophysical properties of a delayed rectifier K+ current can contribute to its role in generating spontaneous myogenic activity.

Salviamiltiorrhiza induces depolarization of pacemaker potentials in murine small intestinal interstitial cells of Cajal via extracellular Ca2+ and Na+ influx.

Interstitial cells of Cajal (ICCs) are pacemaker cells that control smooth muscle contraction in the gastrointestinal(GI) tract. The present study investigated the effects of Salviamiltiorrhiza (SM) on the pacemaker potentials of ICCs from the mouse small intestine invitro and on GI motility invivo. The whole‑cell patch‑clamp configuration was used to record pacemaker potential in ICCs invitro, and GI motility was investigated invivo by recording intestinal transit rate (ITR). Using the whole‑cell patch‑clamp configuration, SM depolarized the pacemaker potentials of ICCs in a dose‑dependent manner. Fulvestrant blocked SM‑induced effects but 1,3‑dihydro‑3,3‑bis(4‑hydroxyphenyl)-7-methyl‑2H‑indol‑2‑one did not. Additionally, 4‑[2‑phenyl-5,7‑bis(trifluoromethyl) pyrazolo[1,5‑a]pyrimidin‑3‑yl] phenol blocked SM‑induced effects. Intracellular guanosine 5'‑O‑(2‑thiodiphosphate), and pretreatment with extracellular Ca2+‑ and Na+‑free solutions also blocked SM‑induced effects. Furthermore, ITR values were increased by SM invivo and SM elevated the levels of motilin(MTL). The SM‑induced increase in ITR was associated with increased protein expression levels of c‑kit and the transmembrane protein16A(TMEM16A) channel. In addition, SM induced pacemaker potential depolarization through estrogen receptor β in a Gprotein‑dependent manner via extracellular Ca2+ and Na+ regulation in the murine small intestine invitro. Moreover, SM increased the ITR invivo through the MTL hormone via c‑kit and TMEM16A‑dependent pathways. Taken together, these results suggested that SM may have the ability to control GI motility and could be used as a GI motility regulator.

The traditional medicine bojungikki-tang increases intestinal motility

Background: Bojungikki-tang (BJIT) is a traditional formula used to treat Gastrointestinal (GI) diseases. Objectives: We investigated the GI motility functions in vivo and the pacemaker potential in interstitial cells of Cajal (ICCs) in vitro by BJIT. Materials and Methods: Intestinal transit rate (ITR) and serum levels of GI hormones were investigated in mice. ICC-induced pacemaker potential was evaluated using the electrophysiological method. Results: ITR values and the level of motilin significantly increased after treatment with BJIT. The BJIT-induced ITR increase was related to the increase in the expression of a c-kit. BJIT induced the pacemaker potential depolarizations and the frequency decrease of ICCs. Pretreatment with methoctramine resulted in the inhibition of BJIT-induced depolarization of the pacemaker potential. However, BJIT-induced effects were retained in the presence of 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide. Furthermore, thapsigargin pretreatment resulted in the inhibition of BJIT-induced effects. Moreover, BJIT blocked both transient receptor potential melastatin 7 and calcium-activated chloride (transmembrane protein 16A) channels. Conclusion: These results indicate that BJIT can be considered a good medicine for controlling GI motility.

Modulation of Fermented Lotus Root on Pacemaker Potentials in Interstitial Cells of Cajal of Murine Small Intestine

Modulation of Fermented Lotus Root on Pacemaker Potentials in Interstitial Cells of Cajal of Murine Small Intestine