The role of dynamic palmitoylation in Ca(2+) channel inactivation

N- and P/Q-type Ca(2+) channels regulate a number of critical physiological processes including synaptic transmission and hormone secretion. These Ca(2+) channels are multisubunit proteins, consisting of a pore-forming α(1), and accessory β and α(2)δ subunits each encoded by multiple genes and splice variants. β subunits alter current amplitude and kinetics. The β(2a) subunit is associated with slowed inactivation, an effect that requires the palmitoylation of two N-terminal cysteine residues in β(2a). In the current manuscript, we studied steady state inactivation properties of native N- and P/Q-type Ca(2+) channels and recombinant N-type Ca(2+) channels. When bovine α(1B) and β(2a) and human α(2)δ were coexpressed in tsA 201 cells, we observed significant variations in inactivation; some cells exhibited virtually no inactivation as the holding potential was altered whereas others exhibited significant inactivation. A similar variability in inactivation was observed in native channels from bovine chromaffin cells. In individual chromaffin cells, the amount of inactivation exhibited by N-type channels was correlated with the inactivation of P/Q-type channels, suggesting a shared mechanism. Our results with recombinant channels with known β subunit composition indicated that inactivation could be dynamically regulated, possibly by alterations in β subunit palmitoylation. Tunicamycin, which inhibits palmitoylation, increased steady-state inactivation of Ca(2+) channels in chromaffin cells. Cerulenin, another drug that inhibits palmitoylation, also increased inactivation. Tunicamycin produced a similar effect on recombinant N-type Ca(2+) channels containing β(2a) but not β(2b) or β(2a) subunits mutated to be palmitoylation deficient. Our results suggest that Ca(2+) channels containing β(2a) subunits may be regulated by dynamic palmitoylation.