beta-Adrenergic receptor stimulation of L-type Ca2+ channels in rabbit portal vein myocytes involves both alphas and betagamma G protein subunits.

1. Previous studies have shown that purified G protein alphas and betagamma subunits stimulate vascular L-type Ca2+ channels through protein kinase A and C (PKA and PKC), respectively. The present study tested whether activation of endogenous G proteins via beta-adrenergic receptor binding also stimulates vascular Ca2+ channels through both Galphas and Gbetagamma and the subsequent activation of PKA and PKC. 2. Peak Ba2+ current (IBa) in freshly isolated rabbit portal vein smooth muscle cells was significantly increased by bath application of 0.5 microM isoproterenol (isoprenaline; ISO) when measured using the whole-cell patch clamp method (53 +/- 3 % increase, n = 15). Stimulation of IBa by ISO was partially reversed by a PKA inhibitor, KT 5720, or a PKC inhibitor, calphostin C, and completely blocked when cells were pretreated with both KT 5720 and calphostin C. 3. Dialysis of cells with polyclonal antibody to Galphas significantly reduced but did not completely eliminate ISO-induced stimulation of IBa. The remaining stimulation was abolished by calphostin C. Dialysis of cells with a polyclonal antibody to Gbeta also significantly reduced ISO-induced stimulation and the remaining stimulation was abolished by KT 5720. Dialysis of cells with both antibodies completely prevented the stimulation of IBa by ISO. 4. ISO-induced stimulation of IBa was reversed by ICI-118,551, a specific beta2-adrenoceptor antagonist, but not by CGP 20712A, a specific beta1-adrenoceptor antagonist. In addition, the beta2-adrenoceptor agonist zinterol significantly increased peak IBa while the beta1-adrenoceptor agonist dobutamine and beta3-adrenoceptor agonist BRL 37344A had little effect on peak IBa. 5. These data suggest that beta-adrenergic receptor stimulation of vascular L-type Ca2+ channels involves both alphas and betagamma G-protein subunits, which exert their effects through PKA and PKC, respectively.