Involvement of both G protein alpha s and ss gamma subunits in ss-adrenergic stimulation of vascular L-type Ca2+ channels

1 Previous data have shown that activation of beta (3)-adrenoceptors stimul ates vascular L-type Ca2+ channels through a Gas-induced stimulation of the cyclic AMP/PKA pathway. The present study investigated whether beta -adren ergic stimulation also uses the G beta gamma /PI3K/PKC pathway to modulate L-type Ca2+ channels in rat portal vein myocytes. 2 Peak Ba2+ current (I-Ba) measured using the whole-cell patch clamp method was maximally increased by application of 10 muM isoprenaline after blocka de of beta (3)-adrenoceptors by 1 muM SR59230A. Under these conditions, the isoprenaline-induced stimulation of IBa was reversed by ICI-118551 (a spec ific beta (2)-adrenoceptor antagonist) but not by atenolol (a specific beta (1)-adrenoceptor antagonist). The beta (2)-adrenoceptor agonist salbutamol increased IBa, an effect which was reversed by ICI-118551 whereas the beta (1)-adrenoceptor agonist dobutamine had no effect on IBa 3 Application of PKA inhibitors (H-89 and Rp 8-Br-cyclic AMPs) or a PKC inh ibitor (calphostin C) alone did not affect the beta (2)-adrenergic stimulat ion of IBa whereas simultaneous application of both PKA and PKC inhibitors completely blocked this stimulation. 4 The beta (2)-adrenergic stimulation of L-type Ca2+ channels was blocked b y a pre-treatment with cholera toxin and by intracellular application of an anti-Gas antibody (directed against the carboxyl terminus of Gas). In the presence of H-89, intracellular infusion of an anti-G beta (com) antibody o r a beta ARK(1) peptide as well as a pre-treatment with wortmannin (a PI3K inhibitor) blocked the beta (2)-adrenergic stimulation of I-Ba 5 These results suggest that the beta (2)-adrenergic stimulation of vascula r L-type Ca2+ channels involves both G alphas and G beta gamma subunits whi ch exert their stimulatory effects through PKA and PI3K/PKC pathways, respe ctively.