Involvement of both G protein αs and βγ subunits in β-adrenergic stimulation of vascular L-type Ca2+ channels

Abstract

1. Previous data have shown that activation of β3-adrenoceptors stimulates vascular L-type Ca2+ 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 Ca2+ channels in rat portal vein myocytes. 2. Peak Ba2+ current (IBa) measured using the whole-cell patch clamp method was maximally increased by application of 10 μM isoprenaline after blockade of β3-adrenoceptors by 1 μM SR59230A. Under these conditions, the isoprenaline-induced stimulation of IBa was reversed by ICI-118551 (a specific β2-adrenoceptor antagonist) but not by atenolol (a specific β1-adrenoceptor antagonist). The β2-adrenoceptor agonist salbutamol increased IBa, an effect which was reversed by ICI-118551 whereas the β1-adrenoceptor agonist dobutamine had no effect on IBa. 3. Application of PKA inhibitors (H-89 and Rp 8-Br-cyclic AMPs) or a PKC inhibitor (calphostin C) alone did not affect the β2-adrenergic stimulation of IBa whereas simultaneous application of both PKA and PKC inhibitors completely blocked this stimulation. 4. The β2-adrenergic stimulation of L-type Ca2+ 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-Gβcom antibody or a βARK1 peptide as well as a pre-treatment with wortmannin (a PI3K inhibitor) blocked the β2-adrenergic stimulation of IBa. 5. These results suggest that the β2-adrenergic stimulation of vascular L-type Ca2+ channels involves both Gαs and Gβγ subunits which exert their stimulatory effects through PKA and PI3K/PKC pathways, respectively.