Binding of Gαo N Terminus Is Responsible for the Voltage-resistant Inhibition of α1A (P/Q-type, Cav2.1) Ca2+ Channels

G-protein-mediated inhibition of presynaptic voltage-dependent Ca(2+) channels is comprised of voltage-dependent and -resistant components. The former is caused by a direct interaction of Ca(2+) channel alpha(1) subunits with G beta gamma, whereas the latter has not been characterized well. Here, we show that the N terminus of G alpha(o) is critical for the interaction with the C terminus of the alpha(1A) channel subunit, and that the binding induces the voltage-resistant inhibition. An alpha(1A) C-terminal peptide, an antiserum raised against G alpha(o) N terminus, and a G alpha(o) N-terminal peptide all attenuated the voltage-resistant inhibition of alpha(1A) currents. Furthermore, the N terminus of G alpha(o) bound to the C terminus of alpha(1A) in vitro, which was prevented either by the alpha(1A) channel C-terminal or G alpha(o) N-terminal peptide. Although the C-terminal domain of the alpha(1B) channel showed similar ability in the binding with G alpha(o) N terminus, the above mentioned treatments were ineffective in the alpha(1B) channel current. These findings demonstrate that the voltage-resistant inhibition of the P/Q-type, alpha(1A) channel is caused by the interaction between the C-terminal domain of Ca(2+) channel alpha(1A) subunit and the N-terminal region of G alpha(o).