Direct Na+-K+ pump stimulation by K+ in cortical collecting tubules: a mechanism for early renal K+ adaptation.
To evaluate the mechanism of increased Na+-K+ pump turnover rate that characterizes the early cortical collecting tubule (CCT) response to K+ loading [Y. Fujii, S. K. Mujais, and A. I. Katz. Am. J. Physiol. 256 (Renal Fluid Electrolyte Physiol. 25): F279-F284, 1989.], we measured ouabain-sensitive 86Rb+ uptake in microdissected rat CCT exposed acutely to elevated ambient K+ in vivo and in vitro. Tubules preincubated in 10 mM K+ had higher 86Rb+ uptake than when preincubated in 5 mM K+ (25.9 +/- 1.2 vs. 18.9 +/- 0.7 pmol.mm-1.min-1, P less than 0.001). KCl infusion (5 mumol.100 g-1.min-1 x 60 min) increased 86Rb+ uptake from 19.2 +/- 1.0 to 31.2 +/- 1.4 pmol.mm-1.min-1, P less than 0.001; the increment was preserved in tubules subsequently treated with monensin or nystatin in vitro, suggesting that pump stimulation was not mediated by increased cell Na+. This conclusion was confirmed in separate experiments in which the effect of K+ on 86Rb+ uptake was not altered by concurrent preincubation with amiloride. Studies with CCT from isolated perfused kidneys and from adrenalectomized animals revealed that stimulation of 86Rb+ uptake by a K+ load occurs rapidly (less than or equal to 5 min) and is independent of hormonal factors. Increased external K+ produces a rapid rise in K+-transporting capacity (turnover rate) of the Na+-K+ pump in CCT. This phenomenon probably represents a direct effect on K+ on the pump and is an important component of the early renal response to increased K+ secretory load.
Fujii
Y
Y
Department of Medicine, Pritzker School of Medicine, University of Chicago, Illinois 60637.
Katz
A I
AI
D000818:Animals; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D007684:Kidney Tubules / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D007700:Kinetics; D008985:Monensin / Q000494:pharmacology; D009761:Nystatin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D009761:Nystatin; D010042:Ouabain; D008985:Monensin; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium