The effects of calcium ions on the depression of cardiac contractility by chloroquine and quinine.

The effects of chloroquine or quinine, 0.04 mg. ml-1 on the ventricular function curve of turtles were determined. Both drugs caused a shift of the curve to the right indicating a reduction in cardiac contractility. This depression of the curve was fully reversed on raising the external calcium concentration from 1.1 mmol.1-1 to 5.8 mmol.1-1 in the case of chloroquine and to 6.7 mmol.1-1 when quinine was used. The observations indicate that calcium ions are able to reverse the cardiodepression induced by chloroquine and quinine.