Acute effects of two natural corticosteroids on the kinetics of the Na+/H+ exchanger in rat renal brush-border membranes
We studied the effect of adrenalectomy and acute hormone replacement, using physiological doses of natural corticosteroids, on the kinetics of the Na+/H+ exchanger in brush border membrane vesicles. We collected the data using the acridine orange uptake technique. Adrenalectomized (ADX) rats present...
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1997
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00084212_v75_n10-11_p1226_Igarreta http://hdl.handle.net/20.500.12110/paper_00084212_v75_n10-11_p1226_Igarreta |
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| Sumario: | We studied the effect of adrenalectomy and acute hormone replacement, using physiological doses of natural corticosteroids, on the kinetics of the Na+/H+ exchanger in brush border membrane vesicles. We collected the data using the acridine orange uptake technique. Adrenalectomized (ADX) rats presented a decreased maximal rate (V(max)) when compared with sham-operated animals (30 000 versus 41 000 fluorescent units/min, respectively). Administration of corticosterone (B) to ADX rats restored V(max) to values above control (up to 66,000 fluorescent units/min). Smaller doses of 18-OH-B led to similar results. K(m) (16 mM) remained the same for all the groups. Amiloride behaved as a pure competitive inhibitor, with a K(i) = 0.02 mM and an I50 = 98 μM (in the presence of 50 mM sodium gluconate). The presence of sodium in the external buffer, before adding the vesicles, inhibited the exchange, with an I50 = 2 mM. We observed, a significant decrease in the Na+/H+ exchanger under non-acidotic conditions in response to adrenalectomy. Acute administration of physiological doses of natural occurring corticosteroids reversed the effect. |
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