Mutations affecting the delayed rectifier potassium current in Drosophila

Mutations and pharmacological agents have been used to resolve and analyze several K+ currents in Drosophila. Mutations that affect channels carrying the voltage-activated IA and the Ca2+-activated I-CF have helped greatly in analyzing the structure, function and regulation of these channels. We now report mutations that selectively affect the delayed rectifier current, I- K. Flies mutagenized with ethylmethanesulfonate were screened for temperatu re-induced paralysis. Paralytic mutants identified in the screen were exami ned for K+ currents in the larval body-wall muscles. The z66 mutant larvae showed a significant reduction in I-K. The mutation did not affect other K currents (IA, ICF, Or ICS) or the Ca2+. channel current in the muscles. An other mutation, z4, which showed reduced I-K, failed to complement z66. Gen etic analysis localized the gene disrupted by z66 and z4 to the left arm of chromosome 3, in the 63A1-63B6 region on polytene chromosomes. The z66 and the z4 mutations, which lie in the Shab K+ channel gene, provide an opport unity to undertake analysis of the functioning of these channels and to stu dy the role of these channels in membrane excitability.