Na+/H+ exchange in mosquito Malpighian tubules

Fluid secretion and intracellular pH were measured in isolated mosquito Mal pighian tubules to determine the presence of Na+/H+ exchange. Rates of flui d secretion by individual Malpighian tubules in vitro were inhibited by 78% of control in the presence of 100 muM 5-(N-ethyl-n-isopropyl)-amiloride (E IPA), a specific inhibitor of Na+/H+ exchange. Steady-state intracellular p H was measured microfluorometrically by using 2',7'-bis(2-carboxyethyl)-5(6 )-carboxyfluorescein in individual Malpighian tubules. Bathing the Malpighi an tubules in 0 mM extracellular Na+ or in the presence of 100 mM EIPA redu ced the steady-state intracellular pH by 0.5 pH units. Stimulation of the N a+/H+ exchanger by using the NH4Cl pulse technique resulted in a rate of re covery from the NH4Cl-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 muM EIPA were 0.7 /- 0.6 and -0.3 +/- 0.3 +/- 10(-3) pH/s, respectively. These results indica te that mosquito Malpighian tubules possess a Na+/H+ exchanger.