Cloning and Tissue Distribution of the Aplysia Na + Channel α-Subunit cDNA

Abstract

Voltage-gated Na⁺ channels generate the depolarizing inward current that is critical for the initiation and conduction of action potentials. To study the roles of Na⁺ channels in neuronal signaling, we have begun the molecular analysis of Na⁺ channels in Aplysia californica. We have isolated cDNAs that encode a neuronal Na⁺ channel α-subunit, which we have named SCAP1. DNA sequence analysis of the SCAP1 cDNA revealed an open reading frame that predicts a protein of 1,993 amino acids, which is highly similar to other members of the Na⁺ channel α-subunit gene family. RNase protection assays carried out on various Aplysia tissues indicated that SCAP1 is expressed predominantly in the nervous system. All of the nonneuronal tissues tested were negative with the exceptions that low levels of expression were observed in ovotestis and parapodium, probably due to the presence of small numbers of neurons within these tissue preparations. Southern blot hybridization at reduced stringency indicated that the genome of Aplysia contains more than one Na⁺ channel α-subunit gene.