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Interaction of ammonia and lithium with the renal micro villus membrane sodium hydrogen ion exchanger


American Journal of Physiology 241(5): C220-C226
Interaction of ammonia and lithium with the renal micro villus membrane sodium hydrogen ion exchanger
The interaction of NH4+ and Li+ with the Na+-H+ exchanger was studied in rabbit renal microvillus membrane vesicles. Alkalinization of the intravesicular space, monitored with [14C]DMO [5,5-dimethoxazolidine-2,4-dione] uptake by flow dialysis, resulted from the addition of Cl- salts of Na+, Li+ or NH4+ to the external medium. The 22Na+ uptake rate, assayed by a rapid filtration technique, was saturable with respect to external Na+ concentration (KT 6 mM Na+) and was competitively inhibited by external Li+ (Ki 1.9 mM) and NH4+ (Ki 4.3 mM). Efflux of 22Na+ from vesicles preloaded with Na+ was stimulated by external Na+ and NH4+ but inhibited by external Li+. Apparently, the renal microvillus membrane Na+-H+ exchanger has affinity for Li+ and NH4+ and can mediate the exchange not only of Na+ for H+ but also of Na+ for Na+, Na+ for NH4+, Li+ for H+ possibly NH4+ for H+, and perhaps Li+ for Na+. The physiological significance of exchange modes other than Na+-H+ exchange is uncertain, but Na+-NH4+ exchange could play a role in the proximal tubular acidification process.

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Accession: 005721462



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