Pathways for HCO-3 exit across the basolateral membrane in rat thick limbs.
We studied the pathways for HCO-3 transport in basolateral membrane vesicles (BLMV) purified from rat medullary thick ascending limbs (MTAL). An inward HCO-3 gradient in the presence of an inside-positive potential stimulated the rate of 22Na uptake minimally and did not induce a 22Na overshoot, arguing against the presence of electrogenic Na+-HCO-3 cotransport in these membranes. An inside-acid pH gradient stimulated to the same degree uptake of 86Rb+ (a K+ analog) with or without HCO-3. Conversely, applying an outward K+ gradient caused a modest intracellular pH (pHi) decrease of approximately 0.38 pH units/min, as monitored by quenching of carboxyfluorescein; its rate was unaffected by HCO-3, indicating the absence of appreciable K+-HCO-3 cotransport. On the other hand, imposing an inward Cl- gradient in the presence of HCO-3 caused a marked pHi decrease of approximately 1.68 pH units/min; its rate was inhibited by a stilbene derivative. Finally, we could not demonstrate the presence of a HCO-3/lactate exchanger in BLMV. In conclusion, the presence of significant Na+-, K+-, or lactate-linked HCO-3 transport could not be demonstrated. These and other data suggest that basolateral Cl-/HCO-3 exchange could be the major pathway for HCO-3 transport in the MTAL.
Leviel
F
F
Laboratoire de Physiologie et Endocrinologie Cellulaire Rénale, Faculté de Médecine Broussais-Hôtel Dieu, Institut National de la Santé et de la Recherche Médicale, Unité 356, 75270 Paris, France.
Eladari
D
D
Blanchard
A
A
Poumarat
J S
JS
Paillard
M
M
Podevin
R A
RA
D000143:Acids / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007672:Kidney Cortex; D007684:Kidney Tubules / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012413:Rubidium / Q000493:pharmacokinetics; D027982:Sodium-Bicarbonate Symporters
D000143:Acids; D001639:Bicarbonates; D002352:Carrier Proteins; D027982:Sodium-Bicarbonate Symporters; D019344:Lactic Acid; D012413:Rubidium