The role of dynamic palmitoylation in Ca2+ channel inactivation

N- and P/Q-type Ca2+ channels regulate a number of critical physiological p rocesses including synaptic transmission and hormone secretion. These Ca2channels are multisubunit proteins, consisting of a pore-forming alpha(1), and accessory beta and alpha(2)delta subunits each encoded by multiple gene s and splice variants. beta subunits alter current amplitude and kinetics, The beta(2a) subunit is associated with slowed inactivation, an effect that requires the palmitoylation of two N-terminal cysteine residues in beta(2a ). In the current manuscript, we studied steady state inactivation properti es of native N- and P/Q-type Ca2+ channels and recombinant N-type Ca2+ chan nels, When bovine alpha(1), and beta(2a) and human alpha(2)delta were coexp ressed in tsA 201 cells, we observed significant variations in inactivation ; some cells exhibited virtually no inactivation as the holding potential w as altered whereas others exhibited significant inactivation. A similar var iability in inactivation was observed in native channels from bovine chroma ffin cells. In individual chromaffin cells, the amount of inactivation exhi bited by N-type channels was correlated with the inactivation of P/Q-type c hannels, suggesting a shared mechanism. Our results with recombinant channe ls with known beta subunit composition indicated that inactivation could be dynamically regulated, possibly by alterations in beta subunit palmitoylat ion, Tunicamycin, which inhibits palmitoylation, increased steady-state ina ctivation of Ca2+ channels in chromaffin cells. Cerulenin, another drug tha t inhibits palmitoylation, also increased inactivation, Tunicamycin produce d a similar effect on recombinant N-type Ca2+ channels containing beta(2a) but not beta(2b) or beta(2a) subunits mutated to be palmitoylation deficien t, Our results suggest that Ca2+ channels containing beta(2a) subunits may be regulated by dynamic palmitoylation.