AJP - Renal Physiology, Vol 245, Issue 5 601-F605, Copyright © 1983 by American Physiological Society
Influence of acute potassium loading on renal phosphate transport in the rat kidney
P. Jaeger, J. P. Bonjour, B. Karlmark, B. Stanton, R. G. Kirk, T. Duplinsky and G. Giebisch
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. Conclusion:
potassium stimulates renal phosphate reabsorption capacity, an effect that
is abolished after TPTX. The potassium effect on phosphate occurs along the
distal tubule.
