The molecular identity of Ca channel alpha 1-subunits expressed in rat sympathetic neurons

Much of our understanding of the mechanisms of the gating, modulation, and function of neuronal Ca channels has its origins in investigations of sympathetic neurons. In this article, we use molecular analyses to identify the three Ca channel alpha 1-subunits that are the likely counterparts to the pharmacologically defined: omega-Conotoxin GVIA-sensitive N-type; dihydropyridine-sensitive L-type, and omega-Conotoxin GVIA-insensitive, dihydropyridine-insensitive Ca channel currents observed in sympathetic neurons. With a combination of degenerate and exact primers, small regions of Ca channel alpha 1-subunit sequences were amplified by the polymerase chain reaction (PCR). Although all five Ca channel alpha 1-subunit genes were expressed in rat sympathetic ganglia, alpha 1B-, alpha 1D-, and alpha 1E-derived cDNAs were the dominant species. No novel Ca channel alpha 1-sequences were identified in the regions selected for amplification, and we conclude that alpha 1B, alpha 1D, and alpha 1E likely encode, respectively, N-type, L-type, and non-N/non-L-type channel currents of rat sympathetic neurons. In addition, we show that Ca channel beta 2-, beta 3-, and beta 4-subunit sequences are strongly represented in sympathetic ganglia. The results of this study also suggest that alpha 1D, and not alpha 1C, regulates Ca influx through dihydropyridine-sensitive Ca channel currents.