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

Stimulation of cardiac L-type Ca2+ channels by cAMP-dependent protein kinas e (PKA) requires anchoring of PKA to a specific subcellular environment by A-kinase anchoring proteins (AKAP). This study evaluated the possible requi rement of AKAP in PKA-dependent regulation of L-type Ca2+ channels in vascu lar smooth muscle cells using the conventional whole cell patch-clamp techn ique. Peak Ba2+ current in freshly isolated rabbit portal vein myocytes was significantly increased by superfusion with either 0.5 mu M isoproterenol (131 +/- 3% of the control value, n = 11) or 10 mu M 8-bromoadenosine 3',5' -cyclic monophosphate (8-BrcAMP; 114 +/- 1%, n = 8). The PKA-induced stimul atory effects of both isoproterenol and 8-BrcAMP were completely abolished by a specific PKA inhibitor KT-5720 (0.2 mu M) or by dialyzing cells with H t 31 (100 mu M), a peptide that inhibits the binding of PKA to AKAP. In con trast, Ht 31 did not block the excitatory effect of the catalytic subunit o f PRA 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.