Cl(-)-dependent NH4+ transport mechanisms in medullary thick ascending limb cells.
To characterize Cl(-)-dependent NH4+ transport mechanisms in renal medullary thick ascending limb (MTAL), intracellular pH (pHi) and membrane potential (PD) were monitored with use of 2',7'-bis(carboxyethyl)- 5(6)-carboxyfluorescein and 3,3'-dipropylthiadicarbocyanine, respectively, in suspensions of rat MTAL tubules in CO2-free media. Exposure of MTAL cells to 4 mM NH4Br caused, after an initial cell alkalinization due to NH3 entry, an NH4(+)-induced fall in pHi that was approximately 67% less pronounced in Cl(-)-free than in Cl(-)-containing media. The following experiments were performed in the presence of 1 microM amiloride to block the MTAL NH4+ conductance. When cells were preincubated in a Cl(-)-free gluconate medium in which K+ and Cl- conductances are greatly reduced, abrupt addition of 100 mN N-methyl-D-glucamine (NMDG)-Cl had no effect on cell PD and pHi in the absence of ammonia, but acutely acidified the cells by approximately 0.2 pH units in the presence of 4 mM NH4Br, which thus indicated nonelectrogenic (NMDG-Cl)-dependent NH4+ influx. The latter also occurred in a Cl(-)-free thiocyanate medium in which the Cl- conductance was blocked by 0.1 mM diphenylamine-2-carboxylate (DPC). An NMDG-Cl- dependent NH4(+)-induced fall in pHi was reduced approximately 33% by 10 mM Ba+, approximately 84% by 0.1 mM bumetanide, and 100% by 1.5 mM furosemide, whereas 1 mM hydrochlorothiazide had no effect; inhibition by Ba+ was observed even in the presence of 0.1 mM verapamil added to block both K+ channels and K+/NH4+ antiport.(ABSTRACT TRUNCATED AT 250 WORDS)
Amlal
H
H
Institut National de la Santé et de la Recherche Médicale Unité 356, Université Pierre et Marie Curie, Paris, France.
Paillard
M
M
Bichara
M
M
D000818:Animals; D001692:Biological Transport; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000502:physiology; D002712:Chlorides / Q000378:metabolism*; D007679:Kidney Medulla / Q000378:metabolism*; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters
D002352:Carrier Proteins; D002712:Chlorides; D000644:Quaternary Ammonium Compounds; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide