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Transport of sodium and secretion of potassium and bicarbonate by the colon of normal and sodium‐depleted rats
Author(s) -
Edmonds C. J.
Publication year - 1967
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1967.sp008380
Subject(s) - bicarbonate , chemistry , sodium , potassium , medicine , sodium bicarbonate , endocrinology , permeability (electromagnetism) , isotonic solutions , extracellular , biophysics , biochemistry , biology , membrane , organic chemistry
1. Ascending and descending colonic segments of normal and Na‐depleted rats were perfused in vivo with isotonic solutions of varying Na concentration and the unidirectional Na fluxes and secretion rate of K and bicarbonate and the transmucosal electrical p.d. were measured. 2. Potential difference was greater in Na‐depleted rats, especially towards the distal end of the descending colon. With reduction of luminal Na concentration, p.d. was reduced. 3. The ascending and descending segments were similar in regard to Na transport except that the latter had lower passive permeability. Na depletion caused an increase of Na influx rate, Na net flux rate and Na exchange diffusion whilst the mucosal passive Na permeability decreased. These changes resulted in a reduction in the critical luminal Na concentration, i.e. the concentration at which the unidirectional fluxes were equal. 4. K secretion rate was similar in the ascending and descending colon and was increased by Na depletion. In all rats, it was reduced when the luminal Na concentration was low. 5. Bicarbonate secretion rate was unaffected by the Na depletion and all solutions remained isotonic during perfusion. 6. The results confirmed that active Na transport was stimulated by Na depletion but indicated that this was probably not the only factor in the elevation of transmucosal p.d.