AJP - Renal Physiology, Vol 251, Issue 4 678-F682, Copyright © 1986 by American Physiological Society
Effects of fasting on citrate transport by the brush-border membrane of rat kidney
D. W. Windus, D. E. Cohn and M. Heifets
Fasting in rats decreases plasma citrate levels and reduces urinary citrate
excretion by the kidney. After 72 h of fasting, the endogenous renal
citrate clearance was decreased and the fractional citrate excretion was
0.026 +/- 0.008 compared with 0.218 +/- 0.030 in control fed rats. To
determine whether these findings result from an adaptation in citrate
transport across the plasma membrane of the renal tubular cell, Na+
gradient-dependent [14C]citrate uptake was examined in brush-border
membrane vesicles (BBMW) prepared from kidneys of fed and 72-h fasted rats.
The initial rate (10 s) of Na+ gradient-stimulated uptake of 100 microM
citrate was significantly increased in BBMW from kidneys of fasted rats
(380 +/- 24.9 pmol/mg prot) compared with fed rats (255 +/- 24.9 pmol/mg
prot). Arterial acid-base parameters from conscious animals were similar
between the two groups. There was no significant difference in
Na+-independent citrate uptake or in L-glutamine uptake measured at 20 s in
BBMV from the kidneys of fasted compared with fed rats. An adaptation
occurs in the brush-border membrane of the renal tubular cell of fasting
rats, unrelated to systemic acidosis, that may result in increased
reabsorption of citrate.
