The transepithelial voltage of the isolated anterior stomach of mosquito larvae (Aedes aegypti): pharmacological characterization of the serotonin-stimulated cells

The lumen-negative transepithelial voltage (V_te) of the isolated and perfused anterior stomach of mosquito larvae (Aedes aegypti) was studied with a `semi-open' preparation in which one end of the gut was ligated onto a perfusion pipette and the other end remained open to the bath. All experiments were performed with serotonin-stimulated preparations. V_te was abolished after addition of 2.5 mmol l^-1 dinitrophenol and depended on the presence of Cl^-. Na⁺ substitution experiments showed that a major part of V_te depended on the presence of this cation in the hemolymph side of the epithelium. Addition of 10 μmol l^-1concanamycin (78±6% inhibition) or 2.5 mmol l^-1 ouabain(15±2% inhibition) to the bath partially inhibited V_te. DPC (0.5 mmol l^-1) or DIDS (0.1 mmol l^-1) reduced V_te when applied to the hemolymph side of the epithelium (to 49±8% or 78±3% of the control,respectively). When present on both sides of the epithelium, these inhibitors caused further V_te reductions (to 23±4% or 35±4% of the control, respectively). Hemolymph-side furosemide (0.1 mmol l^-1) or BaCl₂ (5 mmol l^-1) reduced V_te by 13±3% or 23±4% of the control,respectively. When applied to the hemolymph side of the epithelium, amiloride(0.2 mmol l^-1) significantly decreased V_te by 35±6% of the control, whereas the drug caused no further effect when it was subsequently also applied to the luminal side of the epithelium. The above results are the basis for an extended model for the cellular mechanisms of NaHCO₃ secretion/HCl absorption involved in alkalization of the anterior stomach of mosquito larvae.