Sodium influx in human leucocytes: a novel technique for assessment of sodium-proton antiport activity.
1. A triple-isotope method for measuring initial 22Na uptake rates in unactivated human leucocytes in the presence of serum, using 3H2O, [14C]sucrose and 22Na, is described. 2. This 22Na influx is inhibited by amiloride, with half-maximal inhibition at a concentration of 10(-5) mol/l. 3. About 70% of the 22Na influx in normal human leucocytes is inhibited by 1 mmol/l amiloride, with an external Na+ concentration of 10 mmol/l. 4. External Na+ antagonizes this inhibition by amiloride. The Km for external Na+ is 9 mmol/l. 5. Intracellular acidification from either external Na+ depletion or ammonium chloride incubation leads to an activation of amiloride-sensitive Na+ influx. 6. The amiloride-sensitive Na+-H+ antiport provides the major influx pathway for Na+ in unactivated human leucocytes in the presence of serum.
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Sheikh Rashid Diabetes Unit, Radcliffe Infirmary, Oxford, U.K.
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D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride; D017920:Antiporters; D002021:Buffers; D002352:Carrier Proteins / Q000378:metabolism*; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007962:Leukocytes / Q000187:drug effects / Q000378:metabolism*; D008722:Methods; D011522:Protons; D012964:Sodium / Q000097:blood* / Q000378:metabolism
D017920:Antiporters; D002021:Buffers; D002352:Carrier Proteins; D003470:Culture Media; D011522:Protons; D000643:Ammonium Chloride; D000584:Amiloride; D012964:Sodium