Acid-base maneuvers and phosphate transport in the isolated rat kidney

Abstract

The influence of bicarbonate (HCO ⁻₃ ), the carbon dioxide tension ($p_{CO_2 }$, and pH on phosphate (P_i) excretion were assessed in isolated rat kidneys, perfused in vitro with recirculating synthetic solutions. After establishing control values, the perfusate HCO ⁻₃ or$p_{CO_2 }$ was altered separately. When the perfusate pH was decreased, either by increasing$p_{CO_2 }$ or decreasing HCO ⁻₃ , the absolute and fractional P_i excretions increased. Perfusate alkalinization by slightly decreasing the$p_{CO_2 }$ did not affect P_i excretion, but increasing the perfusate pH with addition of HCO ⁻₃ elicited phosphaturia. Other kidneys were perfused with a solution from which the CO₂/HCO ⁻₃ buffer system was nominally absent. Alkalinization of HCO ⁻₃ -free perfusate had no effect upon P_i excretion, but acidification resulted in marked phosphaturia. Perfusate acidification, whether achieved by decreasing HCO ⁻₃ , increasing$p_{CO_2 }$, or by adding hydrogen ions, uniformly elicited phosphaturia. The data indicate that either decreasing the extracellular pH or increasing the extracellular HCO ⁻₃ inhibits renal P_i reabsorption.