Ca²⁺-activated K⁺ current in freshly isolated c-Kit positive cells in guinea-pig stomach

This study was designed to isolate Ca²⁺-activated K⁺ current (I_KCa) and elucidate its physiological significance in freshly isolated interstitial cells of Cajal (ICCs) of guineapig stomach. Single ICC was freshly isolated by enzymatically dissociating from myenteric border of gastric antrum free of circular muscles, and conventional wholecell voltage clamp technique including immunohistochemical techniques were employed to characterize the cells: In myenteric border of gastric antrum, ICC-MY (ICCs from myenteric border) were detected by immunohistochemical reactivity, and single ICC-MY which has many branches was immunohistochemically c-Kit positive. Under K⁺-rich and 0.1 mM ethylene glycol-bis (2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid pipette solution, ICC produced spontaneous inward current (-256±92.2 pA). When step-depolarizing pulse from -80 to +80 mV was applied at holding potential (V_h) of -80 mV, voltage-dependent outward currents were recorded with superimposed spontaneous transient outward currents (STOCs). Both STOCs and outward currents were reversibly affected by tetraethylammonium chloride (TEA) and iberiotoxin (IbTX); 2 mM TEA and 200 nM IbTX completely abolished STOCs and significantly inhibited outward K⁺ current over the whole potential range tested for current/voltage (I/V) relationship. In addition, TEA delayed repolarization phase of spontaneous inward current. The present results indicate the presence of I_KCa in a single ICC, and it might be involved in regulation of repolarizing phase of spontaneous inward current in guinea-pig stomach.