Multiple G-protein βγ combinations produce voltage-dependent inhibition of N-type calcium channels in rat superior cervical ganglion neurons

Activation of several G-protein-coupled receptors leads to voltage- dependent (VD) inhibition of N- and P/Q-type Ca²⁺ channels via G-protein βγ subunits (Gβγ). The purpose of the present study was to determine the ability of different Gβγ combinations to produce VD inhibition of N-type Ca²⁺ channels in rat superior cervical ganglion neurons. Various Gβγ combinations were heterologously overexpressed by intranuclear microinjection of cDNA and tonic VD Ca²⁺ channel inhibition evaluated using the whole-cell voltage-clamp technique. Overexpression of Gβ1-Gβ5, in combination with several different Gγ subunits, resulted in tonic VD Ca²⁺ channel inhibition. Robust Ca²⁺ channel modulation required coexpression of both Gβ and Gγ. Expression of either subunit alone produced minimal effects. To substantiate the apparent lack of Gβγ specificity, we examined whether heterologously expressed Gβγ displaced native Gβγ from heterotrimeric complexes. To this end, mutant Gβ subunits were constructed that differentially modulated N-type Ca²⁺ and G-protein-gated inward rectifier K⁺ channels. Results from these studies indicated that significant displacement does not occur, and thus the observed Gβγ modulation can be attributed directly to the heterologously expressed Gβγ combinations.