Volume-activated chloride currents in pancreatic duct cells

We have used the patch clamp technique to study volume-activated Cl^– currents in the bicarbonatesecreting pancreatic duct cell. These currents could be elicited by a hypertonic pipette solution (osmotic gradient 20 mOsm/l), developed over about 8 min to a peak value of 91 ± 5.8 pA/pF at 60 mV (n = 123), and were inhibited by a hypertonic bath solution. The proportion of cells which developed currents increased from 15% in freshly isolated ducts to 93% if the ducts were cultured for 2 days. The currents were ATP-dependent, had an outwardly rectifying current/voltage (I-V) plot, and displayed time-dependent inactivation at depolarizing potentials. The anion selectivity sequence was: ClO₄ = I = SCN > Br = NO₃ > Cl > F > HCO₃ > gluconate, and the currents were inhibited to a variable extent by DIDS, NPPB, dideoxyforskolin, tamoxifen, verapamil and quinine. Increasing the intracellular Ca²⁺ buffering capacity, or lowering the extracellular Ca²⁺ concentration, reduced the proportion of duct cells which developed currents. However, removal of extracellular Ca²⁺ once the currents had developed was without effect. Inhibiting protein kinase C (PKC) with either the pseudosubstrate PKC (19–36), calphostin C or staurosporine completely blocked development of the currents. We speculate that cell swelling causes Ca²⁺ influx which activates PKC which in turn either phosphorylates the Cl^– channel or a regulatory protein leading to channel activation.We thank David Stephenson for skilled technical assistance, and Dr. Malcolm Hunter for useful discussions. This work was funded by the National Institutes of Health (grant No. DK 43956), and the Cystic Fibrosis Trust.     

Clotrimazole-sensitive K+ currents regulate pacemaker activity in interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are pacemaker cells for gut peristaltic motor activity. Compared with cardiac pacemaker cells, little is known about mechanisms that regulate ICC excitability. The objective of the present study was to investigate a potential role for clotrimazole (CTL)-sensitive K currents (I(CTL)) in the regulation of ICC excitability and pacemaker activity. ICC were studied in situ and in short-term culture by using the whole cell patch-clamp configuration. In situ, ICC exhibited spontaneous transient inward currents followed by transient outward currents. CTL blocked outward currents, thereby increasing the net inward currents, and depolarized ICC, thereby establishing CTL-sensitive channels as regulators of ICC pacemaker activity. In short-term culture, a I(CTL) was identified that showed increased conductance when depolarized from the resting membrane potential to 0 mV and subsequent inward rectification at further depolarized potentials. The I(CTL) markedly increased with increasing intracellular calcium and was insensitive to the ether-à-go-go-related K channel blocker E-4031 and the large-conductance calcium-activated K channel blocker iberiotoxin. I(CTL) contributed 3-9 nS to the whole cell conductance at 0 mV membrane potential under physiological conditions; it was fast activating (tau = 88 ms), showed little time-dependent inactivation, and exhibited a deactivation time constant of 38 ms. The nitric oxide donor sodium nitroprusside (SNP) increased I(CTL). Single-channel activity, activated by calcium and SNP, was inhibited by CTL, with a single-channel conductance of approximately 38 pS. In summary, ICC generate a I(CTL) on depolarization through an intermediate-conductance calcium-activated K channel that regulates pacemaker activity and ICC excitability.     

Volume-activated chloride currents from human fibroblasts: blockade by nimodipine

The whole-cell patch clamp technique was used to identify and to characterize volume-activated Cl- current (ICl(vol)) in fibroblasts derived from human periodontal ligament. During osmotic cell swelling, the cells exhibited an outwardly rectifying current, which was dependent upon the concentration of external Cl-. The anion permeability sequence of the chloride channel for anions was as follows: SCN- > I- > Br- > Cl- > F- > methanesulphonate > gluconate. Being an inhibitor of Cl- channels and Cl-/HCO exchanger, 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS) inhibited the currents with a voltage-dependence (EC50 57 micromol/l at +80 mV), and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), a carboxylate analogue Cl- channel blocker, showed the reversible suppression of the currents in a dose-dependent manner (EC50 = 59 micromol/l). Nimodipine, a selective dihydropyridine Ca2+ channel blocker suppressed ICl(vol) (EC50 = 66 micromol/l) and the effects were quite similar to those of NPPB. Nifedipine, another DHP blocker also inhibited the currents but with lesser efficacy (EC50 = 139 micromol/l). The removal of external Ca2+ or the addition of Cd2+ in the bath solution did not affect the blocking effects of nimodipine on ICl(vol). These findings demonstrate that the human fibroblasts ICl(Vol) was suppressed by nimodipine in an extracellular Ca2+-independent way. These results may provide, at least in part, an explanation for the Ca2+-independent decrease in Cl-/organic osmolytes efflux and RVD responses by nimodipine in some cell types.     

血管内皮细胞容量激活的氯通道

氯通道是血管内皮细胞上主要的离子通道,容量激活的氯通道是其中一种主要类型并广为研究。已经主宰容量激活的氯通道在维持静息膜电位,调节细胞内钙、ｐＨ值,影响细胞增殖和分化中起着重要的作用。本文综述了血管内皮细胞容量激活氯通道的基本电生理及分子生物学特性,并初步探讨该通道的调节机制。     

睫状体色素上皮细胞容积激活性氯电流

为研究睫状体色素上皮 (pigmentedciliaryepithelial,PCE)细胞容积激活性Cl-电流的特性 ,用膜片箝全细胞记录技术记录了猪的低渗液诱发的容积激活性Cl-电流。此电流外向占优势 ,几乎没有时间依赖性失活 ,电流 电压曲线显示此电流反转电位 (- 6 3± 0 5mV)很接近氯离子平衡电位的计算值 (ECl=0mV)。电流的激活依赖于细胞内ATP ,细胞外ATP抑制外向电流和内向电流 ,但外向电流抑制率大于内向电流抑制率 (92 %比 74% ,P <0 0 1)。氯离子通道阻断剂tamoxifen抑制外向电流和内向电流 ,两个抑制率几乎相等 (85 %比 87% ,P >0 0 5 )。此电流特性与其他类型细胞的P糖蛋白相关电流很相似。结果提示PCE细胞容积激活性Cl-电流的形成可能与P糖蛋白有关     

Pacemaker currents modulated by C-type natriuretic peptide in interstitial cells of Cajal from murine small intestine

Although the presence of C-type natriuretic peptide (CNP) in gastrointestinal tract has been demonstrated, the effect of CNP on interstitial cells of Cajal (ICC), pacemaker cells in gastrointestinal tract, is still unclear. This study was designed to investigate the effect of CNP on pacemaker currents of ICC and possible mechanisms. We used immunocytochemistry techniques to exhibit natriuretic peptide receptors (NPR) and recorded membrane currents by using whole-cell patch clamp technique on cultured ICC. Our experiment showed that NPR-A and NPR-B were expressed in ICC from murine small intestine. Whole cell recordings further showed that the amplitude of pacemaker currents in intestinal small networks of ICC was 322+/-22pA and the frequency was 16.25+/-0.95Hz. CNP significantly reduced the amplitude of pacemaker currents in small networks of ICC in a dose-dependent manner, and the amplitude was inhibited by 23.95%, 61.76% and 81.67%, the amplitude values in 329+/-28.0pA, 311.2+/-14.8pA and 295+/-26.5pA before treatment with CNP and 237.9+/-27.5pA, 119.6+/-18.5pA and 57.2+/-13.5pA after treatment with 0.01 micromolxL(-1), 0.1 micromolxL(-1) and 1pmolxL(-1) CNP, respectively. The frequencies of pacemaker currents were also significantly reduced from 16.25+/-0.95Hz of control to 13+/-0.9Hz, 12+/-0.8Hz and 3+/-0.2Hz by 0.01micromolxL 1, 0.1micromolxL(-1) and 1 micromol x L(-1) CNP, respectively. CNP also inhibited the amplitude of pacemaker currents in single ICC. The inhibitory effect of CNP was mimicked by 8-Br-cGMP, a membrane permeable cGMP analogue, which suggests that CNP could inhibit pacemaker currents via NPR-B-particulate guanylate cyclase (pGC)-cGMP signal pathway.     

Comparative study of interstitial cells of Cajal

The cells present in the alimentary canal, contacting both nerve endings and smooth muscle cells and named interstitial cells of Cajal, show different ultrastructural features. A comparative study has been performed in order to see if these differences can be related to the animal species studied or to the interstitial cell localizations inside the muscle wall of the various levels of the alimentary canal or to their contacts with other cells. Only mammals were considered, and rat, mouse, hedgehog and man have been studied. All the localizations where interstitial cells of Cajal have usually been found were considered: esophagus (body and lower sphincter), stomach (gastric extent of the lower esophageal sphincter, fundus and corpus), small intestine and colon. From this comparison a correlation was found between the morphology and the location of interstitial cells. On the contrary, the morphological differences existing between animal species do not seem to be that consistent. Moreover, the number of contacts between interstitial cells and between these and smooth muscle cells and nerve endings varies according to the interstitial cell location and morphology. It is concluded that the chain nerve endings----interstitial cells of Cajal----smooth muscle cells is not morphologically identical at each gastrointestinal level, and this finding is considered very important in interpreting the role played by the interstitial cells of Cajal in gastrointestinal motility.     

Immunomagnetic enrichment of interstitial cells of Cajal

Disruptions of networks of interstitial cells of Cajal (ICC), gastrointestinal pacemakers and mediators of neurotransmission, can lead to disordered phasic contractions and peristalsis by reducing and uncoupling electrical slow waves. However, detailed analysis of the ICC network behavior has been hampered by their scarcity, limited accessibility in intact tissues, and contamination with other cell types in culture. Our goal was to develop a simple technique to purify ICC from murine gastrointestinal muscles for functional studies. We identified ICC in live small intestinal muscles or primary cell cultures by Kit immunoreactivity using fluorescent antibodies. Because this technique also labels resident macrophages nonspecifically, parallel studies were performed in which nonfluorescent Kit antibodies and macrophages labeled with fluorescent dextran were used for subtractive analysis of ICC. In both groups, Kit-positive cells were tagged with superparamagnetic antibodies and sorted on magnetic columns. Efficacy was assessed by flow cytometry. ICC enrichment from primary cultures and freshly dissociated tissues was approximately 63-fold and approximately 8-fold, respectively. Unlike the cells derived directly from tissues, cells sorted from cultures frequently yielded extensive, nearly homogenous ICC networks on reseeding. Monitoring oscillations in mitochondrial Ca(2+) or membrane potential by imaging revealed spontaneous rhythmicity in these networks. Cells that did not bind to the columns yielded cultures that were depleted of ICC and dominated by smooth muscle cells. In conclusion, immunomagnetic sorting of primary cultures of ICC results in relatively homogenous, functional ICC networks. This technique is less suitable for obtaining ICC from freshly dispersed cells.     

Effects of pine needle extract on pacemaker currents in interstitial cells of Cajal from the murine small intestine

Extracts of pine needles (Pinus densiflora Sieb. et Zucc.) have diverse physiological and pharmacological actions. In this study we show that pine needle extract alters pacemaker currents in interstitial cells of Cajal (ICC) by modulating ATP-sensitive K+ channels and that this effect is mediated by prostaglandins. In whole cell patches at 30 degrees , ICC generated spontaneous pacemaker potentials in the current clamp mode (I = 0), and inward currents (pacemaker currents) in the voltage clamp mode at a holding potential of -70 mV. Pine needle extract hyperpolarized the membrane potential, and in voltage clamp mode decreased both the frequency and amplitude of the pacemaker currents, and increased the resting currents in the outward direction. It also inhibited the pacemaker currents in a dose-dependent manner. Because the effects of pine needle extract on pacemaker currents were the same as those of pinacidil (an ATP-sensitive K+ channel opener) we tested the effect of glibenclamide (an ATP-sensitive K+ channels blocker) on ICC exposed to pine needle extract. The effects of pine needle extract on pacemaker currents were blocked by glibenclamide. To see whether production of prostaglandins (PGs) is involved in the inhibitory effect of pine needle extract on pacemaker currents, we tested the effects of naproxen, a non-selective cyclooxygenase (COX-1 and COX-2) inhibitor, and AH6809, a prostaglandin EP1 and EP2 receptor antagonist. Naproxen and AH6809 blocked the inhibitory effects of pine needle extract on ICC. These results indicate that pine needle extract inhibits the pacemaker currents of ICC by activating ATP-sensitive K+ channels via the production of PGs.     

Sodium current in human intestinal interstitial cells of Cajal

Interstitial cells of Cajal (ICC) generate the electrical slow wave required for normal gastrointestinal motility. The ionic conductances expressed in human intestinal ICC are unknown. The aim of this study was to determine expression of a Na+ current in human intestinal ICC and to determine the effects of the Na+ current on the slow wave. Visually identified, freshly dissociated, single ICC were verified by the presence of c-kit mRNA by using single-cell RT-PCR. Standard whole cell currents were recorded from patch-clamped ICC held at -100 mV between pulse protocols. A Na+ current was identified in human intestinal ICC. The current activated at -55 mV and peaked at -30 mV. Extracellular N-methyl-d-glucamine abolished and QX-314 (500 microM) blocked the Na+ current, but nifedipine and Ni2+ did not. The Na+ current was activated by shear stress. Single-cell RT-PCR detected mRNA for the Na+ alpha-subunit SCN5A in single human intestinal ICC. Lidocaine (200 microm) and QX-314 (500 microM) decreased slow wave frequency, and stretch increased slow wave frequency. A mechanosensitive Na+ channel current is present in human intestinal ICC and appears to play a role in the control of intestinal motor function.     

Protein kinases expressed by interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are involved in the generation of electrical rhythmicity of intestinal muscle and in the transduction of neural inputs in the gut. Although the expression of receptors for neurotransmitters and hormones and some second messengers have been investigated in ICC, the protein kinases present in these cells have not been well documented. This study has demonstrated the immunohistochemical localisation of PKA, PKC and PKC in ICC that were identified by the known ICC marker, c-Kit, in the guinea-pig gut. Other PKCs, PKC , , , , , and , and Ca²⁺-calmodulin-dependent protein kinase II were not localised in ICC. Double labelling studies were conducted on longitudinal muscle–myenteric plexus and external muscle–myenteric plexus preparations of the oesophagus, stomach (fundus, corpus and antrum), duodenum, distal ileum, caecum, proximal and distal colon, and rectum. The three protein kinases were detected in c-Kit-immunoreactive ICC at the level of the myenteric plexus (IC-MY), in the muscle (IC-IM) and at the level of the deep muscular plexus (IC-DMP) in the small intestine. PKA was found in over 90% of IC-IM in all regions examined, and in over 90% of IC-MY in the gastric body and antrum and throughout the small and large intestines. PKC was in the majority of ICC in the gastric body and antrum and in the small intestine, but was largely absent from ICC in the oesophagus, proximal stomach and large intestine. PKC occurred in the majority of ICC in all regions except the rectum. The intensity of staining was greatest for PKA, with PKC giving comparatively weak labelling of ICC. PKA was also detected in myenteric neurons, smooth muscle, macrophages and fibroblast-like cells. PKC labelling occurred in large, multipolar neurons throughout the small and large intestine, as well as in lymph vessels and in capillaries. It is concluded that PKA, PKC and PKC are all present in ICC, with the differences in their localisations suggesting specific roles for each in ICC function.     

Appearance of interstitial cells of Cajal in the human midgut

Several subtypes of the interstitial cells of Cajal (ICC) form networks that play a role in gastrointestinal motor control. ICC express c-kit and depend on signaling via Kit receptors for development and phenotype maintenance. At 7-8 weeks of development, c-kit-immunoreactive (c-kit-IR) cells are present in the human oesophagus, stomach and proximal duodenum wall. In the remaining small and large bowel, c-kit-IR cells appear later. The object of the present study is to determine the timing of the appearance of c-kit-IR ICC in the parts of the digestive tube originating from the midgut (distal duodenum, jejunum, ileum and proximal colon). Specimens were obtained from eight human embryos and 11 fetuses at 7-12 weeks of gestational age. The specimens were exposed to anti-c-kit antibodies to investigate ICC differentiation. The differentiation of enteric neurons and smooth muscle cells was immunohistochemically examined by using anti-PGP9,5 and anti-desmin antibodies, respectively. In the distal duodenum, jejunum and ileum, c-kit-IR cells emerged at week 9 at the level of the myenteric plexus in the form of a thin row of cells encircling the inception of the ganglia. These cells were multipolar or spindle-shaped with two long processes and corresponded to the ICC of the myenteric plexus. In the proximal colon, c-kit-IR cells emerged at week 9-10 in the form of two parallel belts of cells extending at the submucosal plexus and the myenteric plexus levels. We conclude that ICC develop following two different patterns in the human midgut.     

Volume-activated chloride channels in neuroblastoma cells are blocked by the antiestrogen toremifene

Summary The presence of volume-activated chloride channels has been examined in neuroblastoma C1300 cells using the whole-cell configuration of the patch-clamp technique. Chloride channels could not be detected under isotonic conditions. However, hypotonic challenge induced slowly developed inward and outward anionic currents that exhibited outward rectification and inactivation at the most depolarizing potentials, features that were similar to the currents described in other cell preparations where volume-activated Cl^– channels have been associated with the expression of P-glycoprotein. This hypotonicity-activated Cl^– currents could be reversibly blocked by extracellular exposure to toremifene, a novel synthetic antioestrogen. The fact that toremifene and its analog tamoxifen, have been shown to block P-glycoprotein-associated chloride channels and to reverse P-glycoprotein associated multidrug resistance in a number of cell lines suggest that P-glycoprotein could be involved in the generation of hypotomic-induced chloride conductance in neuroblastoma cells.     

Telocytes and interstitial cells of Cajal in the biliary system

A novel type of interstitial tissue cells in the biliary tree termed telocytes (TCs), formerly known as interstitial Cajal‐like cells (ICLCs), exhibits very particular features which unequivocally distinguish these cells from interstitial cells of Cajal (ICCs) and other interstitial cell types. Current research substantiates the existence of TCs and ICCs in the biliary system (gallbladder, extrahepatic bile duct, cystic duct, common bile duct and sphincter of Oddi). Here, we review the distribution, morphology and ultrastructure of TCs and ICCs in the biliary tree, with emphasis on their presumptive roles in physiological and pathophysiological processes.     

内脏平滑肌Cajal间质细胞起搏功能(英文)

胃肠道的大部分区域都存在着一种特殊的间质细胞——Cajal间质细胞(interstitial cells of Cajal,ICCs)。尽管在100多年前它们的存在就已被发现,但是直到最近几十年的研究才逐渐揭示了它们的功能。在胃肠道,ICCs被认为是平滑肌自发性节律性电活动,即"基本电节律"(又称"慢波")的起搏细胞,并介导神经至平滑肌的神经信号传递活动。除胃肠道外,ICC样细胞同样存在于其它内脏平滑肌,如泌尿、生殖系统以及血管平滑肌等。本文仅就这些内脏平滑肌ICCs的功能做一简单综述。     

Identification of interstitial cells of Cajal in the rabbit portal vein

Two layers of interstitial cells (ICs) of Cajal were detected by c-kit and methylene blue staining in the media of the rabbit portal vein in subendothelial intramuscular and deeper intramuscular positions, displaced radially from each other by about 40-70 microm. Two morphologically distinct types of ICs were found among enzymatically dispersed cells from this vessel: small multipolar cells with stellate-shaped bodies not exceeding 20 microm, and spindle-shaped cells from 40 to 300 microm in length with numerous branching processes. Relaxed smooth muscle cells (SMCs) had a more constant length (90-150 microm). The cell membrane capacitance was 46.5+/-2.2 pF in SMCs, 39.7+/-2.4 pF in spindle-shaped ICs and 27.8+/-0.7 pF in multipolar ICs. Although darker under phase contrast, after loading with fluo-4 AM, single isolated ICs of both types usually had brighter fluorescence than SMCs and displayed various spontaneous calcium events, including Ca(2+) sparks and Ca(2+) waves. Ca(2+) waves were usually followed by contraction of SMCs but no change in shape of ICs. In some ICs spontaneous [Ca(2+)](i) transients (lasting about 2s) which propagated towards the end of the processes were observed. Physical contacts between the processes of ICs and the body of one or more SMCs survived the isolation procedure. Application of noradrenaline (1-10 microM), caffeine (1-10 mM) or high-K(+) solution (60mM) led to a rise of [Ca(2+)](i) in both SMCs and ICs evoking contraction of SMCs but not ICs. No differences in electrophysiological characteristics between single enzymatically isolated IC and SMC were detected; thus, the resting membrane potential estimated under current-clamp conditions was -46.5+/-2.0 mV in spindle-shaped ICs and -45.6+/-2.7 mV in SMCs. Under voltage-clamp, both ICs and SMCs revealed a well-developed voltage-gated nifedipine-sensitive L-type Ca(2+) current, a set of K(+) currents, including spontaneous transient outward currents (STOCs) but no Na(+) current. This study for the first time directly demonstrated the presence in vascular tissue of ICs. Possible roles for ICs including their involvement in spontaneous activity of the vessel were discussed.     

Induction of pacemaker currents by DA-9701, a prokinetic agent, in interstitial cells of Cajal from murine small intestine

The interstitial cells of Cajal (ICC) are pacemaking cells required for gastrointestinal motility. The possibility of whether DA-9701, a novel prokinetic agent formulated with Pharbitis Semen and Corydalis Tuber, modulates pacemaker activities in the ICC was tested using the whole cell patch clamp technique. DA-9701 produced membrane depolarization and increased tonic inward pacemaker currents in the voltage-clamp mode. The application of flufenamic acid, a non-selective cation channel blocker, but not niflumic acid, abolished the generation of pacemaker currents induced by DA-9701. Pretreatment with a Ca²⁺-free solution and thapsigargin, a Ca²⁺-ATPase inhibitor in the endoplasmic reticulum, abolished the generation of pacemaker currents. In addition, the tonic inward currents were inhibited by U-73122, an active phospholipase C inhibitor, but not by GDP-β-S, which permanently binds G-binding proteins. Furthermore, the protein kinase C inhibitors, chelerythrine and calphostin C, did not block the DA-9701-induced pacemaker currents. These results suggest that DA-9701 might affect gastrointestinal motility by the modulation of pacemaker activity in the ICC, and the activation is associated with the non-selective cationic channels via external Ca²⁺ influx, phospholipase C activation, and Ca²⁺ release from internal storage in a G protein-independent and protein kinase C-independent manner.