A study on the mechanism of Ligustrazine-induced slow action potential and contraction in guinea pig papillary muscles

The electrophysiological mechanism of Ligustrazine-induced slow action potential (SAP) and contraction in guinea pig papillary muscles was explored using a standard microelectrode technique. It was found that Ligustrazine (3.0 mmol/L) itself induced SAP and contraction in normal and catacholamine-depleted guinea pig papillary muscles, it failed in the beta-adrenoreceptor blocked muscles. Elevation of [Ca/sup 2+/]o from 0.5, 1.0, 2.5 to 5.0 mmol/L increased APA of Ligustrazine induced SAP in a dose dependent manner. A linear relationship existed between APA and lg[Ca/sup 2+/]o with a slope of 22.0 mV for a 10 fold change in [Ca/sup 2+/]o. These results suggested that the Ligustrazine can enhance the slow inward current (Isi) of myocardiac cells and the effect of the Ligustrazine on enhancing Iai may be mediated through activation of beta-adrenoreceptor.