Effects of amiloride on isolated Malpighian tubules of the yellow fever mosquito ( Aedes aegypti)

Abstract

Amiloride (1 mM) significantly reduces transepithelial fluid secretion from 0.62 ± 0.05 to 0.25 ± 0.12 nl/min (23 tubules) in isolated Malpighian tubules of Aedes aegypti. In parallel rates of transepithelial Na, K and Cl secretion decrease respectively to 31, 19 and 28% of control values. In amiloride-treated tubules, db-cAMP (1 mM) significantly increases fluid secretion, but the usual secretagogue effect of db-cAMP is blunted, and in db-cAMP stimulated tubules, amiloride inhibits transepithelial fluid secretion. Amiloride (1 mM) has no effect on transepithelial voltage, and the small effects on basolateral and apical membrane voltage develop slowly with time. Amiloride has no effects on transepithelial resistance and the fractional resistances of the basolateral and apical cell membranes of principal cells. Significant inhibitory effects on the rates of transepithelial Na, K, Cl and fluid secretion but a lack of an effect on transepithelial and membrane fractional resistance are inconsistent with the amiloride block of epithelial Na channels in Aedes Malpighian tubules. Instead major effects on Na, K and Cl transport and minor effects on tubule electrophysiology suggest that amiloride affects electroneutral transport system(s).