title: Glucocorticoid activation of Na+/H+ exchange in renal brush border vesicles: kinetic effects.
abstract: Administration of the synthetic glucocorticoid dexamethasone to adrenalectomized rats increased Na+/H+ exchange activity in isolated renal brush border membrane vesicles. Treatment altered the initial rate of Na+ uptake by increasing Vmax (19.90 +/- 2.17 vs. 27.32 +/- 1.50 nmol.mg protein-1.5 s-1) and not the apparent affinity KNa+ (8.33 +/- 1.11 vs. 7.94 +/- 1.60 mM). Dexamethasone treatment resulted in a proportional increase in 1 mM Na+ uptake at every intravesicular pH measured. When these data were analyzed by the Hill equation, it was found that dexamethasone treatment did not change the apparent number of H+ binding sites (1.24 vs. 1.26) or the [H+]0.5 (0.33 vs. 0.32 microM) but increased the apparent Vmax (0.98 vs. 0.55 nmol.mg protein-1.2 s-1). It was also found that dexamethasone injections of 60 micrograms/100 g body wt resulted in maximum stimulation of exchange activity and that a significant increase in amiloride-sensitive Na+ uptake was detected within 12 h after a single dose of dexamethasone.
mesh_terms: D000315:Adrenalectomy; D000450:Aldosterone / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006859:Hydrogen / Q000378:metabolism*; D007474:Ion Exchange; D007672:Kidney Cortex / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000450:Aldosterone; D000584:Amiloride; D003907:Dexamethasone; D006859:Hydrogen; D012964:Sodium