Gβγ dimers stimulate vascular L-type Ca2+ channels via phosphoinositide 3-kinase

We have previously reported that, in venous myocytes, G beta gamma scavengers inhibit angiotensin AT(1A) receptor-induced stimulation of L-type Ca2+ channels (1). Here, we demonstrate that intracellular infusion of purified G beta gamma complexes stimulates the L-type Ca2+ channel current in a concentration-dependent manner. Additional intracellular dialysis of GDP-bound inactive G alpha(o) or of a peptide corresponding to the G beta gamma binding region of the beta-adrenergic receptor kinase completely inhibited the G beta gamma-induced stimulation of Ca2+ channel currents. The gating properties of the channel were not affected by intracellular application of G beta gamma, suggesting that G beta gamma increased the whole-cell calcium conductance. In addition, both the angiotensin AT(1A) receptor- and the G beta gamma-induced stimulation of L-type Ca2+ channels were blocked by pretreatment of the cells with wortmannin, at nanomolar concentrations. Correspondingly, intracellular infusion of an enzymatically active purified recombinant G beta gamma-sensitive phosphoinositide 3-kinase, PI3K gamma, mimicked G beta gamma-induced stimulation of Ca2+ channels. Both G beta gamma- and PI3K gamma-induced stimulations of Ca2+ channel currents were reduced by protein kinase C inhibitors suggesting that the G beta gamma/PI3K gamma-activated transduction pathway involves a protein kinase C. These results indicate for the first time that G beta gamma dimers stimulate the vascular L-type Ca2+ channels through a G beta gamma-sensitive PI3K.