Isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti spontaneously secrete NaCl, KCl and water across an epithelium of modest transepithelial resistance (40-80 Ωcm2) and high transepithelial voltage (30-70 mV, lumen positive). Transepithelial electrochemical potentials indicate that Na and K are secreted by active and Cl by passive transport mechanisms. The addition of synthetic leucokinin-VIII (LK-VIII, insect myotropic peptide) to the peritubular bath significantly increases the rates of transepithelial NaCl, KCl and water secretion. In parallel, LK-VIII depolarizes the transepithelial voltage from 59.3 to 5.7 mV, decreases the transepithelial resistance from 57.7 to 9.9 Ωcm2, and renders the basolateral and apical membrane voltages nearly equipotential (∼ -90 mV). Unilateral step changes of the [Cl] in the peritubular bath or tubule lumen elicit small transepithelial Cl diffusion potentials in the absence of LK-VIII but large transepithelial Cl diffusion potentials, up to 85% of Nernst equilibrium potentials, in the presence of LK-VIII. In Malpighian tubules treated with dinitrophenol for estimates of the shunt resistance Rsh, LK-VIII reduces Rsh from 52.5 to 5.8 ωcm2. Bilateral reductions of the Cl concentration in tubule lumen and peritubular bath fully restore Rsh to 55.8 Ωcm2in the presence of LK-VIII. LK-VIII has no effects when presented from the luminal side. These results suggest that LK-VIII increases the Cl conductance of the epithelial shunt via a receptor located at the basolateral side of the epithelium.
- Malpighian tubule
- epithelial shunt pathway chloride conductance
- myotropic and diuretic peptides
ASJC Scopus subject areas
- Cell Biology