Effects of aldosterone on Na transport in the toad bladder II. The anaerobic response |
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Authors: | Peter M. Spooner Isidore S. Edelman |
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Affiliation: | Cardiovascular Research Institute and the Departments of Medicine and Biochemistry and Biophysics, University of California, School of Medicine, San Francico, Ca. 94143, U.S.A. |
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Abstract: | The action of aldosterone on active Na+ transport was assessed under aerobic and anaerobic conditions in the isolated urinary bladder of the toad, BUfo marinus. Aldesterone augmented the short-circuit current (Isc) under rigorous anaerobiosis. Four lines of evidence indicate that the increase in anaerobic Isc does not represent an equivalent increase in active Na+ transport: 1. Net Na+ transport, determined by isotopic fluxes, was the same in the aldosterone-treated and control quarter-bladders, and significantly greater than the simultaneously measured Isc. 2. Amiloride, an inhibitor of the apiral entry of Na+, did not reduce the steroid-dependent increase in the anaerobic Isc. 3. Substitution of choline for Na+ in the mucosal medium reduced the magnitude of the anaerobic Isc values did not eliminate the effect of aldosterone. 4. Addition of ouabain, a potent inhibitor of the Na+ pump, partially inhibited the effect of aldosterone on the anerobic Isc but a significant hormonal increment remained. The source of the anaerobic Isc was not identified; an effort was made, however, to determine the dependence of this current on glycolysis. During anaerobics, aldosterone increased the integral Isc by 42% but did not alter lactate production. These results suggest that the steroid-dependent increase in the anaerobic Isc may involve effects on permeability properties of the epithelium rather than on active tranport systems. |
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