EXPRESSION AND SUBUNIT INTERACTION OF VOLTAGE-DEPENDENT CA2+ CHANNELSIN PC12 CELLS

Nerve growth factor (NGF)-induced differentiation in PC12 cells is acc ompanied by changes in the expression of voltage-dependent Ca2+ channe ls. Ca2+ channels are multimeric complexes com posed of at least three subunits (alpha(1), beta, and alpha(2) delta) and are involved in neu ronal migration, gene expression, and neu rotransmitter release. Altho ugh attempts have been undertaken to elucidate NGF regulation oi Ca2channel expression, the changes in subunit composition of these channe ls during differentiation still remain uncertain. In the present study , patch-clamp recordings show that in addition to the previously docum ented L-type and N-type Ca2+ currents, undifferentiated PC12 cells als o express an omega-agatoxin-IVA-sensitive (P/Q-type) component. In add ition,the corresponding mRNA encoding the pore-forming alpha(1) subuni ts for these channels (C, B, and A, respectively) was detected. Likewi se, mRNA for three distinct auxiliary beta subunits (1, 2, 3) were als o found, beta(3) protein being dominantly expressed. Immunoprecipitati on experiments show that the N-type Ca2- channel is associated with ei ther alpha beta(2) or beta(3), subunit and that NGF increases the chan nel expression without affecting its beta subunit association. These r esults (1) indicate that the diversity of Ca2+ currents in PC12 cells arise from the expression of three distinct alpha(1) and three differe nt beta subunit genes; (2) support a model for heterogenous beta subun it association of the N-type Ca2+ channel in a single cell type; and ( 3) suggest that the regulation of the N-type Ca2+ channel during NGF-m ediated differentiation involves an increase in the number of function al channels with no apparent changes In subunit composition.