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Cl- Transport by Gastric Mucosa: Cellular Cl- Activity and Membrane Permeability
T. E. Machen and T. Zeuthen
Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
Vol. 299, No. 1097, The Binding and Transport of Anions in Living Tissues (Dec. 1, 1982), pp. 559-573
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/2395796
Page Count: 15
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The mechanism of Cl- secretion in the isolated, resting (i.e. cimetidine-treated) gastric mucosa of Necturus has been investigated with radioisotopic and electrophysiological techniques. Measurement of transepithelial 36Cl- fluxes (mucosal to serosal (M → S), JCl- ms; S → M, JCl- sm) during control conditions show that at open circuit, when the transepithelial potential difference ψms = 20 mV (S ground), JCl- ms = JCl- sm, i.e. JCl- net = 0, but during short-circuit current conditions JCl- net = Ise = 2 μ equiv cm-2 h. Experiments with low [Cl-] solutions indicate that Cl- exchange diffusion does not contribute significantly to either JCl- ms or JCl- sm. Double-barrelled, Cl--selective microelectrodes showed that in open circuit, the cellular (C) chemical potential for Cl-, ψCl- c = 31 mV (apparent [Cl-] = 29 mM), the electrical potential across the M membrane, ψm = -34 mV (mucosa ground) while that across the S membrane, ψs = -52 mV (serosa ground). During short-circuit current conditions, ψm = ψs = -49 mV and [Cl-]c = 30 mM. The permeability of the M membrane to Cl- (PCl- m) was calculated both from the tracer experiments and the electrode measurements by using the constantfield equation. Short-term (45 s) uptake of 36Cl- at [Cl-]m = 96 mM during short circuit conditions gave PCl- m = 2.6 10-5 cm s-1. Measurement of [Cl-]c by means of the electrodes when [Cl-]m was changed from 96 to 2 mM or from 2 to 96 mM gave PCl- m = 2.9-5.7 10-5 cm s-1. Our results indicate that during open circuit conditions Cl- is accumulated across the S membrane into gastric cells in an energy-requiring step, but since JCl- net = 0, Cl- must leak back into the S solution at a rate equal to the entry rate. When the tissue is short-circuited, Cl- secretion occurs (JCl- net = Ise) owing to the same energy-requiring accumulation of Cl- by the cells and a passive (apparently electrodiffusive) movement across the mucosal membrane.
Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences © 1982 Royal Society