Dioctanoyl-glycerol inhibits L-type calcium current in embryonic chick cardiomyocytes independent of protein kinase C activation.

Diacylglycerol analogs and phorbol esters are used as protein kinase C (PKC) activators to investigate the effect of PKC on L-type calcium current [ICa(L)] in cardiomyocytes. 1-2-dioctanoyl-sn-glycerol (diC8) is a potent analog of diacylglycerol (DAG) which produces positive inotropic effects in guinea-pig atria cardiomyocytes via PKC activation. DiC8 effect on ICa(L), recorded (at 25 degrees C) in whole-cell voltage-clamp, was measured in 17-day-old embryonic chick cardiomyocytes in culture. ICa(L) was recorded in Na+, K(+)-free solution (external) and Ca(2+)-, K(+)-free solution (pipette), with depolarizing steps (to +10 mV) applied from a holding potential of -40 mV. Perfusion with different concentrations of diC8 (from 0.1 to 100 microM) inhibited ICa(L) in a dose-dependent manner, with half-maximal inhibition occurring at 12.5 microM. The effect of diC8 occurred rapidly, the effect beginning within 2 min and being completed within 5 min. In order to determine if the inhibitory effect of diC8 on ICa(L) was through activation of PKC, 25 microM diC8 was applied after pre-incubation of the cardiomyocytes with the PK inhibitors staurosporine (1 microM) or H-7 (50 microM). The effect of diC8 was not prevented by staurosporine or H-7. To further rule out the involvement of PKC in the action of diC8, experiments were performed using another analog of DAG, 1-oleyl-2-acetyl-glycerol (OAG, 50 microM) and Angiotensin-II (A-II, 0.1 microM). OAG failed to produce any effect on ICa(L). A-II, believed to act by activation of PKC did not affect ICa(L) within a test period of 8 min.(ABSTRACT TRUNCATED AT 250 WORDS)