Biochemical properties and subcellular distribution of an N-type calcium hannel α1 subunit

A site-directed anti-peptide antibody, CNB-1, that recognizes the α1 subunit of rat brain class B calcium channels (rbB) immunoprecipitated 43% of the N-type calcium channels labeled by [¹²⁵I]ω-conotoxin. CNB-1 recognized proteins of 240 and 210 kd, suggesting the presence of two size forms of this α1 subunit. Calcium channels recognized by CNB-1 were localized predominantly in dendrites; both dendritic shafts and punctate synaptic structures upon the dendrites were labeled. The large terminals of the mossy fibers of the dentate gyrus granule neurons were heavily labeled, suggesting that the punctate labeling pattern represents calcium channels in nerve terminals. The pattern of immunostaining was cell specific. The cell bodies of some pyramidal cells in layers II, III, and V of the dorsal cortex, Purkinje cells, and scattered cell bodies elsewhere in the brain were also labeled at a low level. The results define complementary distributions of N- and L-type calcium channels in dendrites, nerve terminals, and cell bodies of most central neurons and support distinct functional roles in calcium-dependent electrical activity, intracellular calcium regulation, and neurotransmitter release for these two channel types.