To identify the presence of inwardly rectifying K⁢ channels and its characteristics, membrane currents were measured using a whole-cell patch clamp from isolated gastric myocytes of guinea-pig. Change of external K⁢ concentration from 5 to 90 mM induced an inward current at a holding potential of ⁣80 mV. The high K⁢-induced inward current was blocked by Ba2⁢ and Cs⁢, but not by glibenclamide. With 90 mM K⁢ in bath, the Ba2⁢- and Cs⁢-sensitive currents showed strong inward rectification. Ten mM TEA weakly blocked the inward current only at potentials more negative than ⁣50 mV. With 90 mM K⁢ in bath, hyperpolarizing step pulses from ⁣10 mV induced inward currents, which were inactivated at potentials more negative than ⁣70 mV. Reduction of external K⁢ to 60 mM decreased the amplitudes of the currents and shifted the reversal potential to more negative potential. The inactivation of inward K⁢ current at negative clamp voltage was not affected by removing external Na⁢. These results suggest that the inwardly rectifying K⁢ channels may exist in gastric smooth muscle.