Effects of metoclopramide on slow response action potentials of myocardium

The effects of metoclopramide (Met) on the action potential of rabbit sinus node cells and slow response action potential of guinea pig papillary muscles were studied with the intracellular microelectrodes. Met 10 mumol.L-1 prolonged the action potential duration at 90% repolarization (APD90) of SA node cell and sinus cycle length (SCL). Met 100 mumol.L-1 caused a decrease in action potential amplitude (APA), Vmax and the slope of phase 4 of action potential of SA node cell. APD90 and SCL were prolonged further. For slow response action potential induced by KCl (25 mmol.L-1), Met 100 mumol.L-1 produced a decrease in APA and depolarization rate. Met 10 mumol.L-1 began to suppress the spontaneous electrical activities induced by barium ion. These findings suggest that Met probably has the effect of blocking calcium inward current in myocardium.