Characterization of Na+/H+ exchange in platelets.
Acidification of the cytoplasm of human blood platelets leads to activation of Na+/H+ exchange. As a result, alkalinization occurs that is detectable by an intracellular fluorescent pH indicator. The activity of the exchanger can also be measured by the swelling of platelets suspended in Na-propionate medium using a Coulter Counter: the rapid entry of propionic acid leads to acidification and activation of Na+/H+ exchange with the parallel entry of Na+ and propionic acid leading to osmotic swelling. The Na+/H+ exchanger is sensitive to amiloride and to derivatives that are reported to be more specific inhibitors; it is specific for Na+ and Li+ with no measurable transfer of K+, Rb+ or Cs+; its Km for Na+ is 75 to 90 mM; it displays competitive behavior between Na+ and amiloride; its activity is decreased in cells loaded with Na+ by prolonged ouabain treatment; and it has a high temperature coefficient. These properties are in general similar to those of the exchanger in other cells. It is suggested that the Na+/H+ exchanger plays a role in platelet pH regulation.
Livne
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Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Grinstein
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S
Rothstein
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D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002352:Carrier Proteins / Q000097:blood; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007474:Ion Exchange; D010042:Ouabain / Q000494:pharmacology; D011522:Protons; D012964:Sodium / Q000097:blood*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D010042:Ouabain; D000584:Amiloride; D012964:Sodium