The isolated anterior stomach of larval mosquitoes (Aedes aegypti): Voltage-clamp measurements with a tubular epithelium

The anterior stomach of larval Aedes aegypti was isolated and perfused via two pipettes. For transepithelial voltage (Vte) measurement, the inflow pipette and the bath were connected via agar bridges to calomel electrodes. For voltage-clamping, the lumen of the tissue contained an Ag/AgCl wire held by the outflow pipette, and the preparation was placed in a bath within a spiral of Ag/AgCl wire. After equilibrating the tissue in mosquito saline on both sides, a Vte of - 8 ± 1 mV was measured (± S.E.M., N = 32). Current-voltage curves (± 100 mV) demonstrated ohmic behaviour of the epithelium. Short-circuiting resulted in a current (Isc) of 103 ± 16 μA cm− 2 and a mean transepithelial conductance (Gte) of 11.8 ± 1.3 mS cm− 2 (± S.E.M., N = 32). A Yonath-Civan plot of Gte of individual preparations over the corresponding Isc resulted in a straight line (r2 = 0.8422), indicating that the difference in Isc of individual preparations is mainly based on different transcellular conductances (Gc). This analysis allowed to estimate the mean leak conductance (Gl ≈ 3.9 mS cm− 2) and the mean transcellular electromotive force (Ec ≈ 13 mV). After administering 0.2 μmol L− 1 serotonin, Isc and Gte significantly increased, to 457 ± 49 μA cm− 2 and to 21.3 ± 2.3 mS cm− 2 (± S.E.M., N = 31, P < 0.05), respectively. The Yonath-Civan plot after serotonin resulted again in a straight line (r2 = 0.8219), indicating a mean Gl of about 1 mS cm− 2 and a mean Ec of about 22 mV. Dinitrophenol (2.5 mmol L− 1) almost abolished Isc and significantly reduced Gte (N = 6). Concanamycin A (100 μmol L− 1) reduced Isc by more than 90% without significantly affecting Gte.