Biochemical and Biophysical Evidence for γ2 Subunit Association with Neuronal Voltage-activated Ca2+Channels

Abstract

A novel gene (Cacng2; gamma(2)) encoding a protein similar to the voltage-activated Ca(2+) channel gamma(1) subunit was identified as the defective gene in the epileptic and ataxic mouse, stargazer. In this study, we analyzed the association of this novel neuronal gamma(2) subunit with Ca(2+) channels of rabbit brain, and the function of the gamma(2) subunit in recombinant neuronal Ca(2+) channels expressed in Xenopus oocytes. Our results showed that the gamma(2) subunit and a closely related protein (called gamma(3)) co-sedimented and co-immunoprecipitated with neuronal Ca(2+) channel subunits in vivo. Electrophysiological analyses showed that gamma(2) co-expression caused a significant decrease in the current amplitude of both alpha(1B)(alpha(1)2.2)-class (36.8%) and alpha(1A)(alpha(1)2.1)-class (39.7%) Ca(2+) channels (alpha(1)beta(3)alpha(2)delta). Interestingly, the inhibitory effects of the gamma(2) subunit on current amplitude were dependent on the co-expression of the alpha(2)delta subunit. In addition, co-expression of gamma(2) or gamma(1) also significantly decelerates the activation kinetics of alpha(1B)-class Ca(2+) channels. Taken together, these results suggest that the gamma(2) subunit is an important constituent of the neuronal Ca(2+) channel complex and that it down-regulates neuronal Ca(2+) channel activity. Furthermore, the gamma(2) subunit likely contributes to the fine-tuning of neuronal Ca(2+) channels by counterbalancing the effects of the alpha(2)delta subunit.