Characterization of Na⁺/H⁺ Exchange in Platelets

Summary

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.

Keywords

Sodium - proton exchange - Human platelets

• References

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