title: Effects of fasting on citrate transport by the brush-border membrane of rat kidney.
abstract: 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.
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects; D000818:Animals; D001692:Biological Transport; D002951:Citrates / Q000378:metabolism*; D019343:Citric Acid; D005215:Fasting; D005973:Glutamine / Q000378:metabolism; D007668:Kidney / Q000378:metabolism* / Q000502:physiology; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000502:physiology
chemical_list: D002951:Citrates; D005973:Glutamine; D019343:Citric Acid; D012964:Sodium