Cross-talk between G-protein and protein kinase C modulation of N-type calcium channels is dependent on the G-protein β subunit isoform

The modulation of N-type calcium current by protein kinases and G-proteins is a factor in the fine tuning of neurotransmitter release. We have previously shown that phosphorylation of threonine 422 in the alpha (1B) calcium channel domain I-II linker region resulted in a dramatic reduction in somatostatin receptor-mediated G-protein inhibition of the channels and that the I-II linker consequently serves as an integration center for cross-talk between protein kinase C (PKC) and G-proteins (Hamid, J,, Nelson, D,, Spaetgens, R,, Dubel, S, J,, Snutch, T. P,, and Zamponi, G, W, (1999) J, Biol, Chem, 274, 6195-6202), Here we show that opioid receptor-mediated inhibition of N-type channels is affected to a lesser extent compared with that seen with somatostatin receptors, hinting at the possibility that PKC/G-protein cross-talk might be dependent on the G-protein subtype. To address this issue, we have examined the effects of four different types of G-protein beta subunits on both wild type and mutant alpha (1B) calcium channels in which residue 422 has been replaced by glutamate to mimic PKC-dependent phosphorylation and on channels that have been directly phosphorylated by protein kinase C, Our data show that phosphorylation or mutation of residue 422 antagonizes the effect of G beta (1) on channel activity, whereas G beta (2) G beta (3), and G beta (4) are not affected. Our data therefore suggest that the observed cross-talk between G-proteins and protein kinase C modulation of N-type channels is a selective feature of the G beta (1) subunit.