Ca2+-Activated K+ Current in Freshly Isolated Pacemaker Cell (Interstitial Cells of Cajal, ICC) in Stomach of Adult Animal

Purpose: Spontaneous electrical activities (slow waves) are generated by interstitial cells of Cajal (ICC) in gastrointestinal (GI) tract. From ICC, slow waves spread to neighboring smooth muscle cells via gap junctions passively. Through this mechanism, GI smooth muscle produce spontaneous contraction. In this study, we try to isolate non-cultured single ICC and Ca2+-activated K+ current in adult guinea-pig stomach. Methods: Whole-cell voltage clamp and immunohistochemical study were used. Results: Single ICC and smooth muscle cells were dissociated by enzyme treatment from guinea-pig antrum and mouse. Single smooth muscle cell show spindle like morphology and have no branch. However, single ICC was discernible from smooth muscle cell for its morphology with many branches. Under confocal microscope, single branched cells expressed c-Kit positive activity. However, normal smooth muscle cells do not expressed it specific activity under confocal microscope. In tissue level, we also found ICC network and intramuscular ICC which is sensitive to c-Kit in adult guinea-pig stomach. Under K+−rich and 0.1 EGTA pipette solution, ICC produced spontaneous inward pacemaking current (−329 ± 107.2 pA, N = 14). When step-depolarizing pulse from −80 to +80 mV was applied at holding potential −80 mV, voltage dependent outwad current was produced. And spontaneous transient outward current (STOC) was superimposed on each traces. STOC was also observed by application of ramp-hyperpoarizing pulse from +80 to −120 mV at Vh = −60 mV. Both STOC and outward current was significantly affected by tetraethylammonium chaloride TEA (2 (5 mM), respectively. TEA 2 mM completely blocked STOC and reduced outward K+ current to 80% of the control. Inhibitory effect of TEA was oserved at whole tested potential ranges in current/voltage (I/V) relationship. Conclusions: These result suggested that TEA-sensitive Ca2+-activated K+ current is present in freshly isolated ICC in guinea-pig stomach.