ATP-sensitive K + current and its modulation by substance P in gastric myocytes isolated from guinea pig

To investigate whether ATP-sensitive K + channels exist in gastric smooth muscle of the guinea pig and whether they are modulated by substance P, we recorded lemakalim-activated K + currents from freshly isolated cells using the standard whole-cell configuration. With 0.1 mM ATP and 140 mM K + in the pipette and 90 mM K + in the bath solution and a holding potential of −80 mV, lemakalim (10 μM) activated a glibenclamide-sensitive inward current with a mean amplitude of −224±34 pA. These currents were voltage-independent from −90 to 0 mV and K +-selective. Increasing the intracellular ATP concentrations from 0.1 to 3 mM reduced the lemakalim-activated currents by about five-fold. External barium and cesium inhibited the lemakalim-activated currents in a dose-dependent manner. External tetraethylammonium (10 mM) inhibited the lemakalim-activated currents by 66±15%. Bath application of substance P (5 μM) inhibited the lemakalim-activated currents by 53±13% and this inhibition was absent when 0.5 mM guanosine 5′- O-(2-thiodiphosphate) (GDPβS) was in the pipette. Phorbol 12,13-dibutyrate (PDB) inhibited the lemakalim-activated currents by 71±3%. Chelerythrine (1 μM) reduced the substance P-induced inhibition of lemakalim-activated currents by 22.2±11.3%. These results suggest the presence of ATP-sensitive K + channels in gastric smooth muscle and that substance P inhibits ATP-sensitive K + channels via G-protein through protein kinase C activation.