Lack of influence of volume flux on phosphate reabsorption in the proximal tubule.
We examined the effects of changes in volume flux, with or without changes in sodium flux, on phosphate reabsorption in the proximal convoluted tubule of the rabbit. Experiments were performed: before and after the addition of 10(-5) M ouabain, with a bath of 260, 290, or 320 mosm/kg and a perfusate of 290, and with change in perfusion rate from 15 to 5 nl/min. With the addition of ouabain, volume reabsorption was completely inhibited and phosphate flux decreased significantly. When volume flux was altered without a corresponding change in sodium flux by altering bath osmolality, no change in phosphate flux was noted even though volume flux increased with the hyperosmotic bath and decreased with the hypoosmotic bath. When perfusion rate was decreased from 15 to 5 nl/min, volume reabsorption decreased by 47% and phosphate reabsorption decreased by 45%. Under these circumstances net sodium flux would be expected to decrease. These results are consistent with a relationship between phosphate and sodium, but not fluid, reabsorption. Furthermore, the absence of a relationship between phosphate and volume flux driven by osmotic gradients would suggest that the paracellular pathway is not a significant route of phosphate flux.
D000042:Absorption; D000818:Animals; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D010477:Perfusion; D010710:Phosphates / Q000378:metabolism*; D011817:Rabbits; D011887:Raffinose / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism
D010710:Phosphates; D010042:Ouabain; D012964:Sodium; D011887:Raffinose