PRIMARY STRUCTURE AND FUNCTIONAL EXPRESSION OF THE OMEGA-CONOTOXIN-SENSITIVE N-TYPE CALCIUM-CHANNEL FROM RABBIT BRAIN

The complete amino acid sequence of a rabbit brain calcium channel (BIII) has been deduced by cloning and sequencing the cDNA. The open reading frame encodes 2339 amino acids, which corresponds to an M(r) of 261,167. A phylogenetic tree representing evolutionary relationships indicates that BIII is grouped together with the other rabbit brain calcium channels, BI and BII, into a subfamily that is distinct from the dihydropyridine-sensitive L-type subfamily. Transient expression in cultured skeletal muscle myotubes derived from muscular dysgenic mice demonstrates that the BIII channel mediates an omega-conotoxin-sensitive calcium current with kinetics and voltage dependence like those previously reported for whole-cell N-type current. Cell-attached patch recordings, with isotonic barium as the charge carrier, revealed distinct single channels with an average slope conductance of 14.3 pS.