Anchoring protein is required for cAMP-dependent stimulation of L-type Ca2+ channels in rabbit portal vein

Abstract

Stimulation of cardiac L-type Ca2+ channels by cAMP-dependent protein kinase (PKA) requires anchoring of PKA to a specific subcellular environment by A-kinase anchoring proteins (AKAP). This study evaluated the possible requirement of AKAP in PKA-dependent regulation of L-type Ca2+ channels in vascular smooth muscle cells using the conventional whole cell patch-clamp technique. Peak Ba2+current in freshly isolated rabbit portal vein myocytes was significantly increased by superfusion with either 0.5 μM isoproterenol (131 ± 3% of the control value, n = 11) or 10 μM 8-bromoadenosine 3′,5′-cyclic monophosphate (8-BrcAMP; 114 ± 1%, n = 8). The PKA-induced stimulatory effects of both isoproterenol and 8-BrcAMP were completely abolished by a specific PKA inhibitor KT-5720 (0.2 μM) or by dialyzing cells with Ht 31 (100 μM), a peptide that inhibits the binding of PKA to AKAP. In contrast, Ht 31 did not block the excitatory effect of the catalytic subunit of PKA when dialyzed into the cells. These data suggest that stimulation of Ca2+ channels in vascular myocytes by endogenous PKA requires localization of PKA through binding to AKAP.