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.