AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 4 752-R761, Copyright © 1989 by American Physiological Society

ARTICLES

Active chloride transport in isolated posterior midgut of tobacco hornworm (Manduca sexta)

A. C. Chao, A. R. Koch and D. F. Moffett
Department of Zoology, Washington State University, Pullman 99164-4220.

The short-circuited posterior midgut of larval tobacco hornworm (Manduca sexta) actively transports Cl- from lumen to hemolymph as measured by unidirectional fluxes of 36Cl-. Potentials and Cl- activities in cytosol and goblet cavity were measured using double-barreled Cl--selective microelectrodes. In the short-circuited tissue, the goblet cavity was electrically positive to the bathing solution, and Cl- activity was below electrochemical equilibrium with luminal fluid. The cytosol was electrically negative to the bathing solution, and Cl- activity was above electrochemical equilibrium. Thus Cl- is pumped from goblet cavity into cell. Although the Cl- that is pumped into the cell can cross the basal membrane, its Cl- conductance is quite low. The Cl- conductance is also quite low in apical membranes of columnar cells. Depression of intracellular Cl- after exposure of the luminal side to high HCO-3 suggested that these membranes have a Cl- for HCO-3 exchange mechanism. The paracellular pathway for Cl- comprises approximately 10% of the total transepithelial conductance.

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