Site of reabsorption of citrate and calcium in the renal tubule of the dog

Abstract

Simultaneous reabsorptive patterns of calcium, citrate, sodium, potassium, creatinine, and para-aminohippurate (PAH) were determined by stop-flow technique during the infusion of calcium chloride and the neutral sodium salts of malate, citrate, and ethylenediaminetetraacetate (EDTA). Citrate reabsorption during citrate infusion occurred in the proximal nephron, coinciding with the area of PAH secretion while the calcium reabsorptive minimum was in the distal tubule, coinciding with the pattern of sodium reabsorption. Malate infusion abolishes citrate reabsorption, stimulates the distal secretion of potassium and, despite the marked increase in citrate excretion, fails to increase citrate concentration in renal tissue samples. EDTA infusion obliterates the calcium reabsorption minimum without affecting the more proximal pattern of citrate reabsorption. It is concluded that maximum citrate reabsorption occurs in the proximal region of the nephron distinctly separate from the more distal region of maximum calcium reabsorption.