Regulation of the cardiac L-type calcium channel in L6 cells by arginine-vasopressin

Abstract

L-type Ca2+ channel activity was measured in L6 cells as nifedipine-sensitive barium (Ba2+; 5 mM) influx in a depolarizing salt solution containing 140 mM KCl. Addition of AVP (arginine-vasopressin) during Ba2+ uptake reduced the rate of Ba2+ influx by 60–100%; this was followed by a gradual restoration of the initial rate of Ba2+ uptake. Blockade of PKC (protein kinase C) by pretreatment with 10 μM bisindolylmaleimide did not affect the initial inhibition of Ba2+ influx, but completely abolished the recovery phase. The effect of AVP was half-maximal at 10 nM AVP and was blocked by the V1a receptor antagonist d-(CH2)5-Tyr(Me)-AVP. Activation of Gαs by isoprenaline or cholera toxin antagonized the actions of AVP on Ba2+ uptake. This protection persisted in the presence of the PKA (protein kinase A) inhibitor KT5720, and was not mimicked by agents that increase cAMP. Inhibition of Ba2+ influx was also elicited by ATP and ET (endothelin 1) with an order of effectiveness ET<ATP<AVP. Each of these agents has been reported to act through Gq-coupled receptors. We conclude that activation of Gq-coupled receptors produces a rapid inhibition of the cardiac L-type Ca2+ channel, which is subsequently overcome by activation of PKC.