Sodium pump quantity and turnover in rabbit descending colon at different rates of sodium absorption |
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Authors: | Michael Roden Klaus Turnheim |
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Affiliation: | (1) Pharmakologisches Institut, Universität Wien, Währinger Strasse 13a, A-1090 Wien, Austria |
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Abstract: | 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. |
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Keywords: | Sodium pump Na+,K+-ATPase regulation and turnover Sodium absorption Rabbit colon Aldosterone Basolateral membrane vesicles of epithelial cells Ouabain binding Binding kinetics |
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