Ca2+ and phosphatidylinositol 4,5-bisphosphate stabilize a Gβγ-sensitive state of CaV2 Ca2+ channels

Direct interactions between G-protein betagamma subunits and N- or P/Q-type Ca2+ channels mediate the inhibitory action of several neurotransmitters in the brain. Membrane potential, channel phosphorylation, or auxiliary subunit association tightly regulate these interactions and the consequent inhibition of Ca2+ current. We now provide evidence that intracellular Ca2+ concentration and phosphoinositides play a stabilizing role in this direct voltage-dependent inhibition. Lowering resting cytosolic Ca2+ concentration in Xenopus oocytes expressing Ca(V)2 Ca2+ channels strongly decreased basal as well as phasic, agonist-dependent inhibition of Ca2+ channels by G-proteins. Decreasing phosphoinositide levels also suppressed G-protein inhibition and completely occluded the effects of a subsequent injection of Ca2+ chelator. Similar regulations are observed in mouse dorsal root ganglia neurons. Alteration of G-protein block by these agents is independent of protein phosphorylation, cytoskeleton dynamics, and GTPase or GDP/GTP exchange activity, suggesting a direct action at the level of the Ca2+ channel/Gbetagamma-protein interaction. Moreover, affinity binding experiments of intracellular loops of the Ca(V)2.1 Ca2+ channels to different phospholipids revealed specific interactions between the C-terminal tail of the channel and phosphoinositides. Taken together these data indicate that a Ca2+-sensitive interaction of the C-terminal tail of P/Q channels with the plasma membrane is important for G-protein regulation.