Influence of acute potassium loading on renal phosphate transport in the rat kidney

This study examined 1) whether potassium-induced depression of phosphate excretion is a parathyroid hormone-dependent phenomenon, and 2) whether such stimulation of tubular phosphate reabsorption capacity involves increased phosphate reabsorption in the distal tubule. Potassium was infused into intact rats (25 mumol X min-1 X kg-1) during stepwise addition of phosphate to the infusion and led to a significant drop in phosphate excretion; this effect was abolished in thyroparathyroidectomized (TPTX) animals. In intact rats the maximal tubular Pi reabsorption per milliliter of glomerular filtrate (max TRPi/ml GF) was significantly higher in the potassium group (2.54 +/- 0.06 mumol/ml GF) compared with the control group (2.31 +/- 0.06 mumol/ml GF) (means +/- SE). In TPTX rats no difference in max TRPi/ml GF was observed: 3.44 +/- 0.07 and 3.49 +/- 0.07 mumol/ml GF during potassium and sodium infusion, respectively. Free-flow micropuncture was carried out on superficial distal tubules of intact rats and fluid samples were analyzed for [3H]inulin and phosphorus (electron microprobe). Phosphorus delivery into the distal tubule was similar in control and potassium-loaded rats. Whereas net phosphorus reabsorption along the distal tubule was absent in the control group, intravenous potassium administration stimulated distal phosphorus reabsorption.

potassium stimulates renal phosphate reabsorption capacity, an effect that is abolished after TPTX. The potassium effect on phosphate occurs along the distal tubule.