Sodium pump quantity and turnover in rabbit descending colon at different rates of sodium absorption.
3H-Ouabain binding to isolated epithelia and basolateral membrane vesicles of Na+-transporting epithelial cells of rabbit descending colon was determined to quantify the number of operative Na+-pump sites at different rates of transcellular Na+ transport which was varied over a wide range by chronic dietary Na+ restriction or Na+ loading. Both in intact epithelia and in basolateral membrane vesicles the maximal number of specific ouabain binding sites was higher in preparations from animals transporting Na+ at high rates than in preparations from animals transporting Na+ at low rates. The affinity of ouabain to its binding site and the association and dissociation rate constants were not dependent on the rate of Na+ transport. In intact epithelia the Na+ turnover rate per pump unit was twice as high in tissues with high Na+ transport than in tissues with low Na+ transport. In basolateral membrane vesicles the Na+ turnover rate was considerably higher than in intact epithelia and there was no difference in turnover rate between vesicle preparations obtained from tissues transporting Na+ at high or low rates. Hence, factors within the intact cell appear to control the turnover rate of the Na+-pump.
Roden
M
M
Pharmakologisches Institut, Universität Wien, Austria.
Turnheim
K
K
D000818:Animals; D001693:Biological Transport, Active; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D004847:Epithelial Cells; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism* / Q000493:pharmacokinetics*
D010042:Ouabain; D012964:Sodium