Differential interactions of the C terminus and the cytoplasmic I-II loop of neuronal Ca2+ channels with G-protein α and βγ subunits I. Molecular determination

Abstract

Interactions of G-protein (α (G(α) and βγ subunits (Gβγ) with N- (α(1B)) and P/Q-type (α(1A)) Ca2+ channels were investigated using the Xenopus oocyte expression system. G(i3)α was found to inhibit both N- and P/Q-type channels by receptor agonists, whereas Gβ1 1/4 was responsible for prepulse facilitation of N-type channels. L-type channels (α(1C)) were not regulated by G(α or Gβγ. For N-type, prepulse facilitation mediated via Gβγ was impaired when the cytoplasmic I-H loop (loop 1) was deleted or replaced with the α(1C) loop 1. Gα-mediated inhibitions were also impaired by substitution of the α(1C) loop 1, but only when the C terminus was deleted. For P/Q-type, by contrast, deletion of the C terminus alone diminished Gα-mediated inhibition. Moreover, a chimera of L-type with the α(1B) loop 1 gained Gβγ-dependent facilitation, whereas an L-type chimera with the Nor P/Q-type C terminus gained G(α-mediated inhibition. These findings provide evidence that loop 1 of N-type channels is a regulatory site for Gβγ and the C termini of P/Q- and N-types for Gα.