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 (BI II) has been deduced by cloning and sequencing the cDNA. The open read ing frame encodes 2339 amino acids, which corresponds to an M(r) of 26 1,167. A phylogenetic tree representing evolutionary relationships ind icates that BIII is grouped together with the other rabbit brain calci um channels, BI and BII, into a subfamily that is distinct from the di hydropyridine-sensitive L-type subfamily. Transient expression in cult ured skeletal muscle myotubes derived from muscular dysgenic mice demo nstrates that the BIII channel mediates an omega-conotoxin-sensitive c alcium current with kinetics and voltage dependence like those previou sly reported for whole-cell N-type current. Cell-attached patch record ings, with isotonic barium as the charge carrier, revealed distinct si ngle channels with an average slope conductance of 14.3 pS.