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

Abstract

Diacylglycerol analogs and phorbol esters are used as protein kinase C (PKC) activators to investigate the effect of PKC on l-type calcium current [I Ca(L)] in cardiomyocytes. 1–2-dioctanoyl-sn-glycerol (diC 8) is a potent analog of diacylglycerol (DAG) which produces positive inotropic effects in guinea-pig atria cardiomyocytes via PKC activation. DiC 8 effect on I Ca(L), recorded (at 25°C) in whole-cell voltage-clamp, was measured in 17-day-old embryonic chick cardiomyocytes in culture. I Ca(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 diC 8 (from 0.1 to 100 μ m) inhibited I Ca(L) in a dose-dependent manner, with half-maximal inhibition occurring at 12.5 μ m. The effect of diC 8 occurred rapidly, the effect beginning within 2 min and being completed within 5 min. In order to determine if the inhibitory effect of diC 8 on I Ca(L) was through activation of PKC, 25 μ m diC 8 was applied after pre-incubation of the cardiomyocytes with the PK inhibitors staurosporine (1 μ m) or H-7 (50 μ m). The effect of diC 8 was not prevented by staurosporine or H-7. To further rule out the involvement of PKC in the action of diC 8, experiments were performed using another analog of DAG, 1-oleyl-2-acetyl-glycerol (OAG, 50 μ m) and Angiotensin-II (A-II, 0.1 μ m). OAG failed to produce any effect on I Ca(L). A-II. believed to act by activation of PKC did not affect I Ca(L) within a test period of 8 min. In conclusion, diC 8 inhibits I Ca(L) in late embryonic chick cardiomyocytes, and this effect does not occur through PKC activation. The inhibitory effect of diC 8 appears to be specific for this compound because OAG had no effect.