SODIUM CURRENT-DENSITY CORRELATES WITH EXPRESSION OF SPECIFIC ALTERNATIVELY SPLICED SODIUM-CHANNEL MESSENGER-RNAS IN SINGLE NEURONS

Elements within the first cytoplasmic loop of voltage-gated sodium cha nnels have been implicated in regulating channel function, We have exa mined the role of alternative splicing within the first cytoplasmic lo op of the Drosophila sodium channel gene para in regulating sodium cur rent expression, using single-cell RT-PCR, In addition to a previously described exon (a), we identified a second exon in this region, desig nated exon i. Alternative splicing of exons a and i results in the exp ression of four para transcripts that are present individually or in c ombination within single neurons, Analysis of sodium current density a nd the pattern of para mRNA expression suggested that the presence of exon a was necessary though not sufficient for expression of sodium cu rrents in cultured embryonic neurons, A similar pattern of alternative splicing of para mRNA was also evident in RNA isolated from whole emb ryos. Combined with our observation that the patterns of alternative s plicing of para mRNA change during development, these findings suggest that neuronal sodium current expression in vivo, is also modulated by alternative splicing.