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 R sh, LK-VIII reduces R sh from 52.5 to 5.8 ωcm2. Bilateral reductions of the Cl concentration in tubule lumen and peritubular bath fully restore R sh 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.
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This work was supported by a USDA grant 89-37250-4519 awarded to Dr. Pannabecker and by NSF grant DCB 8403305 awarded to Dr. Beyenbach. The experimental work is primarily the effort of Dr. Pannabecker over a three-year period of postdoctoral training in the laboratory of Dr. Beyenbach. The authors would like to thank Mr. David Hinckley, Ms. Faith Andrews, and Ms. Agueda Oviedo for their assistance in some of the experiments and Mr. F. Dräger (MPI, Dortmund, Germany) for assistance in graphical work. We thank Mr. John Hunt and the Department of Materials Sciences, College of Engineering, Cornell University, for the use of the JOEL 733 electron probe, and Dr. George Kidder for stimulating and fruitful discussions. The manuscript was written by K.W. Beyenbach at the Max Planck Institute für Systemphysiologie, Dortmund, Germany, and was supported by the Humboldt Stiftung of Germany.
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Pannabecker, T.L., Hayest, T.K. & Beyenbach, K.W. Regulation of epithelial shunt conductance by the peptide leucokinin. J. Membarin Biol. 132, 63–76 (1993). https://doi.org/10.1007/BF00233052
- Malpighian tubule
- myotropic and diuretic peptides
- epithelial shunt pathway chloride conductance