Chloride channels in apical membrane patches of stellate cells of Malpighian tubules of Aedes aegypti

Stellate cells of Aedes aegypti Malpighian tubules were investigated using patch-clamp methods to probe the route of transepithelial Cl secretion. Two types of Cl channel were identified in excised, inside-out apical membrane patches. The first Cl channel, type I, had a conductance of 24pS, an open probability of 0.816±0.067, an open time of 867±114ms (mean ± S.E.M., four patches) and the selectivity sequence I≥Cl≫isethionate>gluconate. The I/Cl permeability ratio was 1.48, corresponding to Eisenman sequence I. The type I Cl channel was blocked by 2,2'-iminodibenzoic acid (DPC) and niflumic acid {2-[3-(trifluoromethyl)anilo]nicotinic acid}. The removal of Ca from the Ringer's solution on the cytoplasmic side had no effect on channel activity. The second Cl channel, type II, had a conductance of 8pS, an open probability of 0.066±0.021 and an open time of 7.53±1.46ms (mean ± S.E.M., four patches). The high density and halide selectivity sequence of the type I Cl channel is consistent with a role in transepithelial Cl secretion under control conditions, but it remains to be determined whether these Cl channels also mediate transepithelial Cl secretion under diuretic conditions in the presence of leucokinin.