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Publisher Summary: This chapter discusses the factors that influence renal phosphate reabsorption: the effect of plasma pH, HCO3- concentration, and CO2 pressure, and the effect of acetazolamide. It presents studies that have been performed on intact animals involving a complex chain of events, including parathyroidal parathyroid hormone (PTH) secretion and renal PTH action. Direct effects of the buffer components on inorganic phosphate (Pi) reabsorption in perfused tubules in situ are observed. The pH effects are tested on tubular phosphate transport on two levels, first on the double perfused proximal tubule in situ and then on the isolated brush border membrane vesicles. The data presented on the intact proximal tubular epithelium indicate that luminal acidosis and intracellular alkalosis inhibit the transtubular Pi transport. Parallel experiments with brush border vesicles have revealed that a low pH at the luminal side of the brush border membrane diminishes the effect of Na+ on the Na+-coupled Pi transport, supposedly by inhibiting the binding of Na+ to the Pi transporter.
