Strong alkalinization in the anterior midgut of larval yellow fever mosquitoes (Aedes aegypti): involvement of luminal Na+/K+-ATPase

Abstract

Recently, Na(+)/K(+)-ATPase has been detected in the luminal membrane of the anterior midgut of larval yellow fever mosquitoes (Aedes aegypti) with immunohistochemical techniques. In this study, the possible involvement of this ATPase in strong alkalinization was investigated on the level of whole larvae, isolated and perfused midgut preparations and on the molecular level of the Na(+)/K(+)-ATPase protein. Ouabain (5 mM) did not inhibit the capability of intact larval mosquitoes to alkalinize their anterior midgut. Also in isolated and perfused midgut preparations the perfusion of the lumen with ouabain (5 mM) did not result in a significant change of the transepithelial voltage or the capacity of luminal alkalinization. Na(+)/K(+)-ATPase activity was completely abolished when KCl was substituted with choline chloride, suggesting that the enzyme cannot act as an ATP-driven Na(+)/H(+)-exchanger. Altogether the results of the present investigation indicate that apical Na(+)/K(+)-ATPase is not of direct importance for strong luminal alkalinization in the anterior midgut of larval yellow fever mosquitoes.

Fig. 1

(A) Midgut isolated from a fourth-instar larval A. aegypti after 60 min incubation in water containing 0.04% mcresol purple. (B) Midgut isolated from a fourth-instar larval A. aegypti after 60 min incubation in water containing 0.04% m-cresol purple and 5 mM ouabain. (C) Transepithelial voltage (V_te) of isolated anterior midgut preparations (N = 7, −S.E.M.) bathed in oxygenated mosquito saline with 0.2 μM serotonin and perfused with NaCl (100 mM) containing 0.04% m-cresol purple with (right column) and without (left column) luminal ouabain (5 mM). The photos below the graph show one example preparation after 5 min of perfusion stop.