The spontaneous contractions of gastric smooth muscles are regulated by slow waves, which are modulated by both nervous system and humoral agents. This study was designed to examine the effects of prostaglandin E2 (PGE2) on the contractile and electrical activities of antral smooth muscles in guinea-pig stomach, using an intracellular recording technique. To elucidate the underlying mechanism for its effect on contractility, ionic currents were also measured using a whole-cell patch clamp method. The basal tone by PGE2 was variable, whereas the magnitude of phasic contractions was reduced (19.0⁑2.1%, n=19). The resting membrane potentials were hyperpolarized (⁣4.4⁑0.5 mV, n=10), and plateau potentials were lowered (⁣2.9⁑0.5 mV, n=10). In most cases, however, the initial peak potentials of slow waves were depolarized more by PGE2 than those of control. The frequency of the slows wave was increased from 5.7⁑0.2 cycles/min to 6.5⁑0.2 (n=22). Voltage-operated Ca2⁢ currents were decreased by PGE2 (n=5). Voltage-operated K⁢ currents, both Ca-dependent and Ca-independent, were increased (n=5). These results suggest that PGE2 plays an important role in the modulation of gastric smooth muscle activities, and its inhibitory effects on the contractility and activities of slow waves are resulted from both decrease of Ca2⁢ currents and increase of K⁢ currents.