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 presented a decreased maximal rate (Vmax) when compared with sham-operated animals (30,000 versus 41,000 fluorescent units/min, respectively). Administration of corticosterone (B) to ADX rats restored Vmax 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 Ki = 0.02 mM and an I50 = 98 microM (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.
Igarreta
P
P
PRHOM (CONICET), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina.
Calvo
J C
JC
Paladini
A
A
Damasco
M C
MC
D015069:18-Hydroxycorticosterone / Q000494:pharmacology*; D000136:Acid-Base Equilibrium / Q000187:drug effects; D000315:Adrenalectomy; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D003345:Corticosterone / Q000494:pharmacology*; D004232:Diuretics / Q000494:pharmacology; D007668:Kidney / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D007700:Kinetics; D008297:Male; D008871:Microvilli / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
D000893:Anti-Inflammatory Agents; D004232:Diuretics; D017923:Sodium-Hydrogen Exchangers; D015069:18-Hydroxycorticosterone; D000584:Amiloride; D012964:Sodium; D003345:Corticosterone