Effect of oxymatrine on beating of cultured myocardial cells in vitro

Oxymatrine (OM), extracted from Sophora alopecuroides L, increased the contractility of the left heart atrium and decreased the spontaneous beating rate of right atrium of rabbit as described in our previous paper. The effect of OM on the beating rate of cultured rat myocardial cells was observed in the present study by a method of recording photoelectric energy transformation. OM 50 mumol/L decreased the beating rate of the myocytes by 50 +/- 27% 15 min after administration and also antagonized the positive chronotropic effect of isoproterenol 1.5 mumol/L, while the negative chronotropic effect of OM was completely abolished by prazosin. However, OM 250 mumol/L accelerated the beating rate of myocytes, which was cancelled by propranolol. These results suggest that OM has biphasic effects on cultured rat myocytes: slowing rate by alpha-adrenoceptor stimulation with 50 mumol/L concentration and accelerating rate by beta-adrenoceptor stimulation with 250 mumol/L concentration.