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.
Background/Aims: Reduction in renal mass by uninephrectomy induces a functional compensation in the remnant kidney. The activity of the angiotensin-converting enzyme (ACE) as well as renin mRNA in the proximal convoluted tubule (PCT) of uninephrectomized (UNx) rats increases. The aim of this work was to determine whether the increased activity of the local renin-angiotensin system (RAS) participates in the adaptation of renal function after uninephrectomy. Method: We utilized normal two-kidney (2K) and 3-week UNx rats to study the activity of the ACE in vesicles obtained from luminal membranes of proximal tubular cells and the acidification kinectics in PCTs using micropuncture techniques. Results: The converting enzyme activity was significantly larger in UNx (5.87 ± 0.69 nmol · min–1 · mg protein–1) than in 2K rats (2.43 ± 0.13 nmol · min–1 · mg protein–1; p < 0.05). The acidification rate constant (κ) in PCT of 2K rats was 0.18 ± 0.02 s–1 and in UNx rats 0.30 ± 0.04 s–1 (p < 0.001). In UNx rats, microperfusion with 10–5 M ramipril or 10–5 M losartan decreased κ to 0.19 ± 0.02 and 0.18 ± 0.02 s–1, respectively, but had no effect on 2K rats. Luminal steady-state pH (pH∞) was the same in 2K and UNx rats, and was not modified by addition of 10–5 M ramipril or 10–5 M losartan in both groups. The proximal H+ flux (JH+), calculated from pH∞ and κ, was 1.12 nmol · cm–2 · s–1 in 2K rats and, 1.77 nmol · cm–2 · s–1 in UNx rats (p < 0.001). In 2K rats, this value was not changed by 10–5 M ramipril or 10–5 M losartan, but in UNx rats JH+ decreased 25 and 30% with ramipril or losartan, respectively (p < 0.001). Conclusions: These data suggest that the increase in the local RAS activity could be an adaptive change that contributes to maintain the homeostasis of body fluids after uninephrectomy.
The normal aging process is accompanied by a progressive deterioration of renal function. We studied the kinetics of proximal tubular acidification of young (3 mo) and aging (22 mo) rats using in vivo and in vitro techniques. Blood acid-base parameters were similar in both groups. The maximum velocity of the Na(+)/H(+) exchange (NHE) in brush-border membrane vesicles (BBMV) showed a 72% decrease in aging compared with young rats, whereas the Michaelis constant remained unchanged. The NHE3 isoform of the Na(+)/H(+) exchanger was detected in BBMV by Western blot in both groups, and a decrease of 90% in the abundance was observed in aging rats. Micropuncture experiments with simultaneous luminal and peritubular perfusion with phosphate Ringer and continuous measurement of intratubular pH showed an acidification rate constant 34% smaller in aging compared with young rats. Proton flux was 48% lower in aging than in young rats. The present results suggest that proximal tubular acidification is impaired with aging.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.