Effect of bath and luminal potassium concentration on ammonia production and secretion by mouse proximal tubules perfused in vitro.
To determine the effects of acute changes in K+ concentration in vitro on ammonia production and secretion by the proximal tubule, we studied mouse S2 segments perfused with and bathed in Krebs-Ringer bicarbonate buffers containing various K+ concentrations. All bath solutions contained L-glutamine as the ammoniagenic substrate. High bath and luminal K+ concentrations (8 mM), but not high luminal K+ concentration alone, inhibited total ammonia production rates by 26%, while low bath and luminal K+ concentrations (2 mM), but not low luminal K+ concentration alone, stimulated total ammonia production rates by 33%. The stimulation of ammonia production by low bath K+ concentration was not observed when L-glutamine was added to the luminal perfusion solution. On the other hand, high luminal K+ concentration stimulated, while low luminal K+ concentration inhibited, net luminal secretion of total ammonia in a way that was: (a) independent of total ammonia production rates, (b) independent of Na(+)-H+ exchange activity, and (c) not due to changes in transepithelial fluxes of total ammonia. These results suggest that luminal potassium concentration has a direct effect on cell-to-lumen transport of ammonia.
Nagami
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Nephrology Section, Veterans Administration Medical Center, West Los Angeles, California 90073.
D000584:Amiloride / Q000494:pharmacology; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000187:drug effects / Q000502:physiology; D005973:Glutamine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D051379:Mice; D011188:Potassium / Q000494:pharmacology*; D012636:Secretory Rate / Q000187:drug effects; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D005973:Glutamine; D000641:Ammonia; D000584:Amiloride; D011188:Potassium