Active chloride transport in isolated posterior midgut of tobacco hornworm (Manduca sexta).
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.
Chao
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AC
Department of Zoology, Washington State University, Pullman 99164-4220.
Koch
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AR
Moffett
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DF
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D004068:Digestive System Physiological Phenomena; D004553:Electric Conductivity; D007915:Lepidoptera / Q000502:physiology*; D008839:Microelectrodes; D009036:Moths / Q000502:physiology*
D001639:Bicarbonates; D002712:Chlorides