Inhibitory action of 3,4-dihydroxybenzaldehyde on membrane potential duration and contraction of papillary muscles in guinea pigs

The electrophysiological effects of 3,4-dihydroxybenzaldehyde (DB), a soluble extract from root of Salvia miltiorrhiza Bunge, on action potential (AP) and contraction of papillary muscles in right ventricles of guinea pigs were examined with the aid of conventional intracellular microelectrodes. The effects of DB on effective refractory period (ERP) and excitability were also observed by using the technique of stimulating and recording in the same cell through a single microelectrode. DB (30-300μg/ml) markedly shortened action potential duration (APD), and suppressed or eliminated the phase 2 of AP, while within the same range of concentrations it increased the repolarizing rate of the phase 3 of AP. DB up to 400μg/ml had no significant influence on the rising rate of the phase O of AP, excitability and at (K+)0=6 mmol/L. ERP was shortened as well as APD, but the rate of ERP/APD90 was slightly enlarged. In the presence of DB, reduction of peak contraction force of papillary muscle was observed. The changes of contraction force were linear with those of APD. The direct Ca++ entrance block mechanism was ruled out and finally it was concluded that DB increased the permeability to K+ and decreased the time constant of repolarizing current IK.