Real-time assessment of alpha-ketoglutarate effect on organic anion secretion in perfused rabbit proximal tubules.
To determine the quantitative roles of the basolateral and luminal Na(+)-dicarboxylate (Na-DC) cotransporters in establishing and maintaining the alpha-ketoglutarate (alphaKG) gradient required for renal tubular secretion of organic anions, we measured net steady-state transepithelial secretion of fluorescein (FL) in real time in isolated, perfused S2 segments of rabbit renal proximal tubules. Net "basal" FL secretion in the absence of exogenous alphaKG had a K(t) of approximately 4 microM and a maximal transepithelial secretion rate (J(max)) of approximately 380 fmol. min(-1). mm(-1) (where K(t) is the FL concentration that produces one-half the J(max)). It could be almost completely inhibited by basolateral p-aminohippurate (PAH). Selective inhibition of the basolateral Na-DC cotransporter indicated that recycling via this transporter of alphaKG that had been exchanged for FL supports approximately 25% of the "basal" FL secretion. Physiological alphaKG concentrations of 10 microM in the bath or 50 microM in the perfusate stimulated net secretion of FL by approximately 30 or approximately 20%, respectively. These data indicate that the basolateral Na-DC cotransporter supports approximately 42% of the net FL secretion. The luminal and basolateral effects of physiological concentrations of alphaKG were additive, indicating that the combined function of the luminal and basolateral Na-DC cotransporters can support approximately 50% of the net FL secretion. This apparently occurs by their establishing and maintaining approximately 50% of the outwardly directed alphaKG gradient that is responsible for driving basolateral FL/alphaKG exchange. The remaining approximately 50% would be maintained by metabolic production of alphaKG in the cells.
Shuprisha
A
A
Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona 85724, USA.
Lynch
R M
RM
Wright
S H
SH
Dantzler
W H
WH
D000818:Animals; D000838:Anions / Q000378:metabolism*; D002352:Carrier Proteins / Q000502:physiology; D003199:Computer Systems; D003287:Contrast Media / Q000493:pharmacokinetics; D029382:Dicarboxylic Acid Transporters; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D019793:Fluorescein / Q000493:pharmacokinetics; D066298:In Vitro Techniques; D007656:Ketoglutaric Acids / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000502:physiology; D029363:Organic Anion Transporters, Sodium-Dependent; D010477:Perfusion; D011817:Rabbits; D027981:Symporters; D010130:p-Aminohippuric Acid / Q000494:pharmacology
D000838:Anions; D002352:Carrier Proteins; D003287:Contrast Media; D029382:Dicarboxylic Acid Transporters; D007656:Ketoglutaric Acids; D008565:Membrane Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; C092524:SLC13A2 protein, human; D027981:Symporters; D019793:Fluorescein; D010130:p-Aminohippuric Acid