Decay of prepulse facilitation of N type calcium channels during G protein inhibition is consistent with binding of a single Gβγ subunit

We have examined the modulation of cloned and stably expressed rat brain N type calcium channels (alpha(1B) + beta(1b) + alpha(2) delta subunits) by exogenously applied purified G protein beta gamma subunits, In the absence of G(beta gamma), barium currents through N type channels are unaffected by application elf strong depolarizing prepulses, In contrast, inclusion of purified G(beta gamma) In the patch pipette results in N type currents that initially facilitated upon application of positive prepulses followed by rapid reinhibition, Examination of the kinetics of G(beta gamma)-dependent reinhibition showed that as the duration between the test pulse and the prepulse was increased, the degree of facilitation was attenuated In a monoexponential fashion, The time constant tau for the recovery from facilitation was sensitive to exogenous G(beta gamma), so that the inverse of tau linearly depended on the G(beta gamma) concentration. Overall, the data are consistent with a model whereby a single G(beta gamma) molecule dissociates from the channel during the prepulse, and that reassociation of G(beta gamma) with the channel after the prepulse occurs as a bimolecular reaction.