Na(+)/H(+) exchange in mosquito Malpighian tubules

Fluid secretion and intracellular pH were measured in isolated mosquito Malpighian tubules to determine the presence of Na(+)/H(+) exchange. Rates of fluid secretion by individual Malpighian tubules in vitro were inhibited by 78% of control in the presence of 100 microM 5-(N-ethyl-n-isopropyl)-amiloride (EIPA), a specific inhibitor of Na(+)/H(+) exchange. Steady-state intracellular pH was measured microfluorometrically by using 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein in individual Malpighian tubules. Bathing the Malpighian tubules in 0 mM extracellular Na(+) or in the presence of 100 microM EIPA reduced the steady-state intracellular pH by 0.5 pH units. Stimulation of the Na(+)/H(+) exchanger by using the NH(4)Cl pulse technique resulted in a rate of recovery from the NH(4)Cl-induced acute acid load of 8.7 +/- 1.0 x 10(-3) pH/s. The rates of recovery of intracellular pH after the acute acid load in the absence of extracellular Na(+) or in the presence of 100 microM EIPA were 0.7 +/- 0.6 and -0.3 +/- 0.3 x 10(-3) pH/s, respectively. These results indicate that mosquito Malpighian tubules possess a Na(+)/H(+) exchanger.