Alterations in the expression and gating of drosophila sodium channels by mutations in the para gene

Mutations in the para gene specifically affect the expression of sodium currents in Drosophila. While 65% of wild-type embryonic neurons in culture express sodium currents, three distinct mutations in the para locus resulted in a decrease in the fraction of cells from which sodium currents could be recorded. This reduction was allele-dependent: macroscopic sodium currents were exhibited in 49% of the neurons in parat ts1 cultures, 35% in para ts2 , and only 2% in para ST76 . Voltage-clamp experiments demonstrated that the para ts2 mutation also affected the gating properties of sodium channels. These results provide convincing evidence that para, a gene recently shown to exhibit sequence similarity to vertebrate sodium channel α subunits, encodes functional sodium channels in Drosophila. The finding that one para allele ( paras ST76 ) can virtually eliminate the expression of sodium currents strongly argues that the para gene codes for the majority of sodium channels in cultured embryonic neurons.