Effects of sodium tanshinone II-A sulfonate on electrical and mechanical properties of myocardium

Tanshinone II-A was extracted from the root of Salvia miltiorrhiza Bunge. Its sodium sulfonate (T) is water soluble and used in this experiment. Cell membrane potentials in sinoatrial node, atrium and ventricle were recorded by microelectrodes. T shortened the duration of the action potentials with little influence on phase 0 and suppressed slow response and sinus automaticity. Synchronous recordings of myocardial contraction with cell membrane potentials in pig trabecular carneae cordis revealed a simultaneous alteration of mechanical (T=4-400 microg/ml) and electrical (T=40-400 microg/ml) activities. The results suggest that T influences the inward Ca2+ current, while the evidence of the separation between two dose-response relationship of electrical and mechanical activities implies another mechanism corresponding to negative inotropic effect of T rather than Ca2+-antagonism.