[Relationship between the positive inotropic action of matrine and extracellular calcium]

Matrine (Ma) was extracted from the seed and leaves of Sophora alopecuroides L. Ma showed positive inotropic actions in isolated guinea pig left atrium and rat vas deferens under electric stimulation. The positive inotropic actions were markedly inhibited by verapamil (1 mumol/L). Isolated rat vas deferens under the action of Ma showed rhythmic contraction. High K+ (KCl 40 mmol/L) augmented the frequency of rhythmic contraction induced by Ma; conversely, Ma may also augment the increased tension produced by high K+. These results suggest that, the positive inotropic actions of Ma is relevant to its activation of Ca2+ channels.