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 24 pS, an open probability of 0.816+/−0.067, an open time of 867+/−114 ms (mean +/− s.e.m., four patches) and the selectivity sequence I(−)>Cl(−)(much greater than) isethionate>gluconate. The 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(2+) 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 8 pS, an open probability of 0.066+/−0.021 and an open time of 7.53+/−1.46 ms (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.

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