Fluid absorption in the isolated midgut of adult female yellow fever mosquitoes (Aedes aegypti)

In the present study, the transepithelial voltage (Vte) and the volume of isolated posterior midguts of adult female yellow fever mosquitoes (Aedes aegypti) were monitored. In all experiments, the initial Vte after filling the midgut was lumen negative, but subsequently changed to lumen positive values at a rate of approximately 1 mV min−1. Simultaneously, the midgut volume decreased, indicating spontaneous fluid absorption. When the midguts were filled and bathed with mosquito saline, the average rate of fluid absorption was 36.5±3.0 nL min−1 (N=4,±s.e.m.). In the presence of theophylline (10 mM), Vte reached significantly higher lumen positive values, but the rate of fluid absorption was not affected (N=6). In the presence of NaCN (5 mM), Vte remained close to 0 mV (N=4) and fluid absorption was reduced (14.4±1.3 nL min−1, N=3,±s.e.m.). When midguts were filled with buffered NaCl (154 mM plus 1 mM HEPES) and bathed in mosquito saline with theophylline, fluid absorption was augmented (50.0±5.8 nL min−1, N=12,±s.e.m.). Concanamycin A (10 µM), ouabain (1 mM), and acetazolamide (1 mM) affected Vte in different ways, but all reduced fluid absorption by 60 to 70% of the value before addition of the drugs.