AJP - Renal Physiology, Vol 251, Issue 5 889-F896, Copyright © 1986 by American Physiological Society
Effect of acute acidemia on phosphate uptake by renal proximal tubular brush-border membranes
B. S. Levine, J. A. Kraut, D. R. Mishler and P. W. Crooks
Prolonged metabolic acidosis is associated with depressed phosphate (Pi)
uptake by the brush-border membrane (BBM) of the proximal tubule. To
examine if changes in systemic pH underlie this inhibition, we measured Pi
transport by renal cortical BBM from thyroparathyroidectomized rats with
respiratory or metabolic acidosis of 1 or 3 h, respectively, and in
appropriate controls. Also, Pi transport was measured in BBM prepared using
tissue slices from nonacidotic rats that were preincubated for 20 or 45 min
at either pH 6.9 (HCO3 = 10 mM, CO2 = 10%) or 7.4 (HCO3 = 10 mM, CO2 =
2.5%). Despite comparable acidemia (pH 7.06 +/- 0.05 with respiratory
acidosis and 7.10 +/- 0.03 with metabolic acidosis), Na-dependent Pi uptake
at 5 s incubation was reduced by 15.2 +/- 3.5% with respiratory acidosis
compared with paired controls. It was not altered with metabolic acidosis.
Vmax in respiratory acidosis (1.2 nmol X mg protein-1 X 5 s-1) was less
than in controls (1.6); Kt was similar in both groups. 22Na transport and
Na-dependent glucose transport were unchanged. Plasma phosphorus (P)
increased from 8.75 +/- 0.35 mg/dl to 12.42 +/- 1.9 with respiratory
acidosis. Therefore BBM vesicles transport was measured in controls after
plasma P was raised. Under these conditions, Pi transport was similar to
that with respiratory acidosis. Also Pi transport by BBM was unchanged when
tissue slices were preincubated in vitro at high CO2 concentrations for 20
or 45 min. Thus respiratory acidosis specifically inhibits Na-dependent Pi
transport by decreasing the number or rate of the BBM Pi carrier.(ABSTRACT
TRUNCATED AT 250 WORDS)
