Phorbol Ester and Dioctanoylglycerol Stimulate Membrane Association of Protein

We used left ventricular myocytes from adult rats to investigate the effect of 4f.-phorbol 12-myristate 13-acetate (PMA) and of sn-1,2-dioctanoylglycerol (DiC-8) on the membrane association of protein kinase C (PKC), cytosolic [Ca2], (Cai) homeostasis, and the contractile properties of single cardiac cells. Because PKC activity is known to be highly Ca2+ sensitive, the K+ concentration of the bathing medium was raised from 5 to 30 mM in some experiments, a perturbation known to depolarize the cell and increase Cai. In cell suspensions both PMA (3 x 10and 3X i0` M) and DiC-8 (10-` and 10-4 M) increased membrane association of PKC. The effect ofPMA (10-` M) on PKC translocation was enhanced in 30 mM KCI compared with 5 mM KCI. During steady field stimulation at 1 Hz in 1 mM bathing [Ca2+], both PMA (10-` M) and DiC-8 (10-` M) decreased twitch amplitude to approximately 60% of control in