Actions of NAD+ on renal brush border transport of phosphate in vivo and in vitro

1985 ◽  
Vol 249 (6) ◽  
pp. F948-F955 ◽  
Author(s):  
S. A. Kempson ◽  
S. T. Turner ◽  
A. N. Yusufi ◽  
T. P. Dousa
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Competitive Inhibition ◽  
Inhibitory Effect ◽  
Pi Transport ◽  
Renal Brush Border Membrane ◽  
Dependent Transport ◽  
Renal Brush Border

Previous studies showed that an increase in NAD+ content in renal cortex in vivo was accompanied by specific inhibition of Na+-dependent inorganic phosphate (Pi) transport across the renal brush border membrane (BBM). Further, in vitro addition of NAD+ to isolated renal BBM vesicles specifically inhibited Na+ gradient-dependent transport of Pi. The present study examined some aspects of the mechanism of this inhibition by NAD+ in vitro and in vivo. When NAD+ was increased in vivo by nicotinamide injection, the apparent Vmax was decreased, but the apparent Km was not different, indicating apparent noncompetitive inhibition. In the presence of 0.3 mM NAD+ added in vitro, the apparent Km for Na+-dependent Pi transport by BBM vesicles was increased, whereas the apparent Vmax was unchanged, indicating apparent competitive inhibition. These changes in apparent Km and apparent Vmax were identical when Pi uptake was measured either at 30-s or at 5-s (the initial rate) incubation times. Inhibition of Pi transport by BBM vesicles in vitro was due primarily to the action of intact added NAD+, although there may be some contribution by isotope dilution due to Pi released from NAD+ by enzymatic hydrolysis. Although in vitro inhibition of Pi transport by added NAD+ was reversed by washing the BBM, the inhibition due to increased NAD+ in vivo persisted after extensive washing of the isolated BBM. The specificity of the inhibitory effect of NAD+ in vivo was indicated by the finding that changes in renal cortical content of ATP or Pi, evoked by loading with glycerol or fructose, did not change BBM transport of Pi.(ABSTRACT TRUNCATED AT 250 WORDS)

Gentamicin inhibits carrier-mediated dipeptide transport in kidney

1996 ◽  
Vol 270 (3) ◽  
pp. F531-F538
Author(s):  
H. A. Skopicki ◽  
D. Zikos ◽  
E. J. Sukowski ◽  
K. A. Fisher ◽  
D. R. Peterson
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Morphological Changes ◽  
Membrane Vesicles ◽  
Renal Brush Border Membrane ◽  
Dipeptide Transport ◽  
Vitro Effect ◽  
Renal Brush Border

The effect of gentamicin on transport of pyroglutamylhistidine (pGlu-His) was examined in rabbit renal brush-border membrane vesicles (BBMV). Gentamicin, an aminoglycoside antibiotic, is limited in its usage because of nephrotoxicity characterized in part by transport defects in the proximal tubule. Since there is no information regarding the effects of gentamicin on renal peptide carriers, uptake of [3H]pGlu-His was measured in BBMV following either in vivo or in vitro exposure to the antibiotic. One hour after in vivo administration, the maximal rate (Vmax) for pGlu-His transport was significantly reduced in isolated membrane vesicles washed free of the drug, but the apparent Michaelis constant (Km) was unaltered. Coincubation of membranes with gentamicin during measurements of pGlu-His uptake had a similar effect, causing a significant decrease in the Vmax but not the Km of transport. The addition of 5 mM magnesium to the uptake medium prevented the in vitro but not the in vivo effect. The data indicate that high doses of gentamicin inhibit the capacity but not the affinity of dipeptide transport in the kidney, prior to morphological changes which typify acute tubular necrosis. The in vitro effect is rapid and involves a direct action of gentamicin on the brush-border membrane. The in vivo experiments show that toxicity may be prolonged and remains following removal of the drug from the renal brush border.

Effects of maleic acid on renal phosphorus transport: role of dietary phosphorus

1991 ◽  
Vol 261 (2) ◽  
pp. F227-F237
Author(s):  
J. Guntupalli ◽  
V. Delaney ◽  
E. J. Weinman ◽  
D. Lyle ◽  
M. Allon ◽  
...  
Keyword(s):  
Maleic Acid ◽  
Competitive Inhibition ◽  
Membrane Vesicle ◽  
Intraperitoneal Administration ◽  
Inhibitory Effect ◽  
Phosphorus Transport ◽  
Dietary Phosphorus ◽  
Pi Transport

The effects of maleic acid on renal phosphate (Pi) transport were examined by clearance and brush-border membrane vesicle (BBMV) transport studies. In normal rats, maleic acid 50 mg.kg body wt-1.h-1 increased the phosphaturia (P less than 0.001). Intraperitoneal administration of a similar dose of maleic acid decreased the BBMV uptake of Pi but not glucose. In rats fed a low-phosphate diet (0.03%), the maleic acid-induced phosphaturia was blunted, but the inhibitory effect on the BBMV transport of Pi persisted. In chronic parathyroidectomized rats fed a low-phosphate diet, where the filtered load of Pi was higher than in the previous groups, the phosphaturia was abolished, but the inhibition of the BBMV transport of Pi was sustained. Both the in vitro incubation of BBMVV and in vivo administration of maleic acid were associated with a competitive inhibition of Pi transport. These studies indicate that the maleic acid-induced phosphaturia is expressed at the apical membrane entry step of Pi, and the enhanced distal tubular reabsorption accounts for the lack of phosphaturia in dietary Pi deprivation.

Different mechanisms of adaptive increase in Na+-Pi cotransport across renal brush-border membrane

1989 ◽  
Vol 256 (5) ◽  
pp. F852-F861 ◽  
Author(s):  
A. N. Yusufi ◽  
M. Szczepanska-Konkel ◽  
A. Hoppe ◽  
T. P. Dousa
Keyword(s):  
Thyroid Hormone ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Actinomycin D ◽  
Biochemical Mechanism ◽  
Phosphonoformic Acid ◽  
Phlorizin Binding ◽  
Renal Brush Border Membrane ◽  
Renal Brush Border

We explored the biochemical mechanism by which thyroid hormone (T3) and low-phosphate diet (LPD) cause an adaptive increase in Na+-Pi cotransport across renal brush-border membrane (BBM). The rate of Na+-Pi cotransport was determined by 32Pi uptake by BBM vesicles (BBMV), and the number of Na+-Pi symporters was assessed by binding of [14C]phosphonoformic acid (PFA) on BBMV. In BBMV of both T3-treated rats and LPD-fed rats, the Na+ gradient-dependent 32Pi uptake increased (Vmax increased; Km Pi was not changed). The Na+-dependent [14C]PFA binding on BBMV increased (higher Vmax, no change in Km PFA) in response to T3, but it remained unchanged in rats fed LPD. Both the increase of Na+-Pi cotransport and of Na+-dependent [14C]PFA binding in response to T3 were blocked by actinomycin D or cycloheximide. Addition of benzyl alcohol to BBMV in vitro increased Na+-Pi cotransport, but [14C]PFA binding did not change; the [3H]phlorizin binding and cotransports of other solutes decreased or did not change. The exposure of BBMV to cholesterol decreased Na+-Pi cotransport without changing [14C]PFA binding. We suggest that the adaptive increase of Na+-Pi cotransport elicited by T3 is due to an increase in number of Na+-Pi cotransporters in BBM. In contrast, in response to LPD the number of Na+-Pi cotransporters is unchanged, and the increased Na+-Pi cotransport is due to faster translocation of Na+ with Pi due to enhanced fluidity of BBM.

Ontogeny of DA1 receptor-mediated natriuresis in the rat: in vivo and in vitro correlations

1992 ◽  
Vol 263 (3) ◽  
pp. R631-R638 ◽  
Author(s):  
S. Kaneko ◽  
F. Albrecht ◽  
L. D. Asico ◽  
G. M. Eisner ◽  
J. E. Robillard ◽  
...  
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Receptor Subtypes ◽  
Renal Brush Border Membrane ◽  
Natriuretic Effect ◽  
Old Rats ◽  
22Na Uptake

The natriuretic and diuretic effects of dopamine are attenuated in the young. Because dopamine has actions on receptors (e.g., adrenergic, serotonin) other than dopamine, we studied a novel dopamine agonist, pramipexole, which has a selectivity to both DA1 and DA2-receptor subtypes. Intravenous administration of pramipexole resulted in a dose-related (1, 10, and 100 micrograms.kg-1.min-1) increase in urine flow and absolute and fractional sodium excretion and a decrease in mean arterial pressure (MAP) in three groups of rats studied. Pramipexole induced a greater decrease in MAP in 6- to 7- (n = 5) and 9- to 16- (n = 6) than in 3- to 4-wk-old (n = 8) rats; the natriuresis and diuresis were greatest in 12- to 16- and least in 3- to 4-wk-old rats. The renal effects of pramipexole were mainly due to actions at the DA1 receptor, since these effects were completely blocked by the coinfusion of a DA1 antagonist, SKF 83742. To explore further a cause of the attenuated natriuretic effect of pramipexole in the young, we studied the effect of a selective DA1-receptor agonist, fenoldopam, on amiloride-sensitive 22Na+ uptake in renal brush-border membrane vesicles. The 3-s amiloride-sensitive uptake was inhibited (45%) by fenoldopam (5 x 10(-5)M) in 9- to 16- (n = 6) but not in 3- to 4-wk-old (n = 5) rats. These studies suggest that the attenuated natriuretic effect of dopamine in the young is in part due to decreased DA1 action on the brush-border membrane Na(+)-H+ exchanger.

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