Effects of Prostaglandin E<SUB>2</SUB> on the Spontaneous Contractions and Electrical Activities of the Antral Circular Muscle in Guinea-pig Stomach

Effects of Prostaglandin E<SUB>2</SUB> on the Spontaneous Contractions and Electrical Activities of the Antral Circular Muscle in Guinea-pig Stomach

<P> 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 E<SUB>2</SUB> (PGE<SUB>2</SUB>) 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 PGE<SUB>2</SUB> was variable, whereas the magnitude of phasic contractions was reduced (19.0&#8273;2.1%, n=19). The resting membrane potentials were hyperpolarized (&#8291;4.4&#8273;0.5 mV, n=10), and plateau potentials were lowered (&#8291;2.9&#8273;0.5 mV, n=10). In most cases, however, the initial peak potentials of slow waves were depolarized more by PGE<SUB>2 </SUB>than those of control. The frequency of the slows wave was increased from 5.7&#8273;0.2 cycles/min to 6.5&#8273;0.2 (n=22). Voltage-operated Ca<SUP>2&#8290;</SUP> currents were decreased by PGE<SUB>2</SUB> (n=5). Voltage-operated K<SUP>&#8290;</SUP> currents, both Ca-dependent and Ca-independent, were increased (n=5). These results suggest that PGE<SUB>2 </SUB>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 Ca<SUP>2&#8290;</SUP> currents and increase of K<SUP>&#8290;</SUP> currents.