Differential inotropic and chronotropic effects of various protein kinase C activators on isolated guinea pig atria.

1,2-Dioctanoylglycerol (10-100 microM) produced a positive inotropic effect on electrically stimulated left guinea pig atria and increased the frequency of spontaneously beating atria. Various phorbol esters and mezerein induced heterogeneous responses of the left atria. Phorbol dibutyrate and phorbol didecanoate decreased the force of contraction to different extents, whereas phorbol myristate acetate and mezerein had dual actions: an initial enhancement followed by a decline in force. None of these compounds changed the spontaneous atrial rate.