Revisiting the cellular mechanisms of strong luminal alkalinization in the anterior midgut of larval mosquitoes.
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 micro mol l(-1) concanamycin (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 BaCl(2) (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 NaHCO(3) secretion/HCl absorption involved in alkalization of the anterior stomach of mosquito larvae.