ONKEN, H; MOFFETT, SB; MOFFETT, DF; Washington State Univ., Pullman; Washington State Univ., Pullman; Washington State Univ., Pullman: The anterior stomach of larval mosquitoes (Aedes aegypti): Voltage-clamping a tubular epithelium.

The anterior stomach of larval A. aegypti was isolated and perfused with a push-pull syringe pump via two perfusion pipettes. At the inflow pipette the tissue was held in place between pieces of soft neoprene foam. At the outflow end a holding pipette was used. The lumen of the tissue contained an Ag/AgCl wire held by the outflow pipette. The preparation was placed in a bath within a spiral of Ag/AgCl wire. For transepithelial voltage (V_te) measurement, the inflow pipette and the bath were connected via agar bridges to calomel electrodes. The two Ag/AgCl wires were used to inject current for voltage-clamping. The epithelial surface was calculated after measuring length and diameter of the preparation with an ocular micrometer. After equilibrating the tissue in mosquito saline on both epithelial sides, a V_te of �8�1 mV was measured (�SEM, N=20). Short-circuiting resulted in a current (I_sc) of 124�23 &microA/cm² and a transepithelial conductance (G_te) of 15.2�1.8 mS/cm² (�SEM, N=20). Plotting G_te of individual preparations over the related I_sc according to Yonath and Civan, resulted in a straight line (r=0.89), indicating that that different I_sc of individual preparations is based on different transcellular conductances (G_c). From the graph, the mean leak conductance (G_l=6.5 mS/cm²) and the mean transcellular electromotive force (E_c=14.3 mV) were estimated. After administering 0.2 &microM serotonin, I_sc and G_te increased to 592�59 &microA/cm² and 28.9�3.0 mS/cm² (�SEM, N=20). The Yonath-Civan plot resulted again in a straight line (r=0.89) with a mean G_l of 2.5 mS/cm² and a mean E_c of 22.4 mV. These results indicate that serotonin increases the transport rate of the epithelium by increasing E_c and G_c. Financial support by NSF (IBN-0091208) is gratefully acknowledged.