Interaction of NH4+ and Li+ with the renal microvillus membrane Na+-H+ exchanger.
We have examined the interaction of NH4+ and Li+ with the Na+-H+ exchanger in rabbit renal microvillus membrane vesicles. Alkalinization of the intravesicular space, monitored with [14C]DMO 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 by 22Na+ from vesicles preloaded with Na+ was stimulated by external Na+ and NH4+ but inhibited by external Li+. We conclude that 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 not certain at present, but Na+-NH4+ exchange could play a role in the proximal tubular acidification process.
D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004114:Dimethadione / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D007700:Kinetics; D008094:Lithium / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism*; D009994:Osmolar Concentration; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers
D001639:Bicarbonates; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000641:Ammonia; D008094:Lithium; D004114:Dimethadione