Effect of adrenomedullin on excitation-contraction coupling and abnormal automaticity in excised human atrial muscles

Direct effect of adrenomedullin(AM)on myocardial cells is as yet equivocal.In addition，the mechanism underlying the direct action of AM on cardiac muscle reams not clear.We have investigated the direct effect of AM on action potential and contraction of papillary muscle excised from guinea pig right，ventricle。The substances at.Concentration ranging from 10个D1-8个D1 to 10个D1-6个D1M caused a slight prolongation of action potential duration at 20%level of the repolarization and an increase of developed tension.This effect.Was abolished in the presence of L-type Ca I D 12+I D 1 channel blocker，suggesting that the positive inotropic effect produced by AM is due to enhancement of L-type Ca I D 12+I D 1 possibly via activation of intracellular cAMP.However，it is reported that AM showed a negative inotropic effect。On rabbit and ferret cardiac muscle。On the other hand，we found that AM might not，induce any effect on slope of pacemaker potential of action potential in rabbit sinoatrial node cell。Further studies into both direct action and its node on cardiac muscles of various mammalian species including human myocardial cells are necessary。

Direct effect of adrenomedullin (AM) on myocardial cells is as yet equivocal. In addition, the mechanism underlying the direct action of AM on cardiac muscle reams not clear. We have investigated the direct effect of AM on action potential and contraction of papillary muscle excised from guinea pig right, ventricle. The substances at. Concentration ranging from 10ィイD1-8ィエD1 to 10ィイD1-6ィエD1 M caused a slight prolongation of action potential duration at 20% level of the repolarization and an increase of developed tension. This effect. Was abolished in the presence of L-type CaィイD12+ィエD1 channel blocker, suggesting that the positive inotropic effect produced by AM is due to enhancement of L-type CaィイD12+ィエD1 possibly via activation of intracellular cAMP. However, it is reported that AM showed a negative inotropic effect. On rabbit and ferret cardiac muscle. On the other hand, we found that AM might not, induce any effect on slope of pacemaker potential of action potential in rabbit sinoatrial node cell. Further studies into both direct action and its node on cardiac muscles of various mammalian species including human myocardial cells are necessary.