Involvement of both G protein αs and βγ subunits in β‐adrenergic stimulation of vascular L‐type Ca 2+ channels

Previous data have shown that activation of β 3 ‐adrenoceptors stimulates vascular L‐type Ca 2+ channels through a Gαs‐induced stimulation of the cyclic AMP/PKA pathway. The present study investigated whether β‐adrenergic stimulation also uses the Gβγ/PI3K/PKC pathway to modulate L‐type Ca 2+ channels in rat portal vein myocytes. Peak Ba 2+ current (I Ba ) measured using the whole‐cell patch clamp method was maximally increased by application of 10 μ M isoprenaline after blockade of β 3 ‐adrenoceptors by 1 μ M SR59230A. Under these conditions, the isoprenaline‐induced stimulation of I Ba was reversed by ICI‐118551 (a specific β 2 ‐adrenoceptor antagonist) but not by atenolol (a specific β 1 ‐adrenoceptor antagonist). The β 2 ‐adrenoceptor agonist salbutamol increased I Ba , an effect which was reversed by ICI‐118551 whereas the β 1 ‐adrenoceptor agonist dobutamine had no effect on I Ba . Application of PKA inhibitors (H‐89 and Rp 8‐Br‐cyclic AMPs) or a PKC inhibitor (calphostin C) alone did not affect the β 2 ‐adrenergic stimulation of I Ba whereas simultaneous application of both PKA and PKC inhibitors completely blocked this stimulation. The β 2 ‐adrenergic stimulation of L‐type Ca 2+ channels was blocked by a pre‐treatment with cholera toxin and by intracellular application of an anti‐Gαs antibody (directed against the carboxyl terminus of Gαs). In the presence of H‐89, intracellular infusion of an anti‐Gβ com antibody or a βARK 1 peptide as well as a pre‐treatment with wortmannin (a PI3K inhibitor) blocked the β 2 ‐adrenergic stimulation of I Ba . These results suggest that the β 2 ‐adrenergic stimulation of vascular L‐type Ca 2+ channels involves both Gαs and Gβγ subunits which exert their stimulatory effects through PKA and PI3K/PKC pathways, respectively.British Journal of Pharmacology (2001) 132 , 669–676; doi: 10.1038/sj.bjp.0703864