POTASSIUM UPTAKE AND RELEASE BY HUMAN-BLOOD PLATELETS

Google Scholar
  • 1 January 1976
    • journal article
    • research article
    • Vol. 48  (2) , 185-197
Abstract
Thrombin is known to reduce the K+ content of human platelets, but the subcellular origin of the lost K+ is not known. The effect of aggregating agents on K+ release was studied in platelets labeled in plasma by preincubation with 42KCl. Platelets were separated from plasma by gel filtration through Sepharose 2B equilibrated with K+-free Tyrode''s buffer. Platelet K+ was 116 neq/108 platelets, of which 23% was extracellular immediately after gel filtration. K+ influx was 65 neq/108 platelets/h at pH 7.5 and was more rapid at pH 7.9. About 70% of cell K+ exchanged with plasma in 4 h with 1st-order kinetics, while a minor fraction of about 30% exchanged with a slower time course. This slowly exchanging fraction of platelet K+ probably arose from heterogeneity in the platelet population. Epinephrine and ADP aggregated gel-filtered platelets and released serotonin, but with loss of only 5%-10% of cell K+ and no .beta.-glucuronidase. In contrast, thrombin released up to 30% of platelet K+, whether aggregation occurred or was prevented by not stirring the cells. The specific activity of K+ released by all aggregating agents was identical to the specific activity of total platelet K+. Thrombin (0.1-0.2 NIH U/ml) released serotonin and also .beta.-glucuronidase (an enzyme of the .alpha.-granule), and there was a linear relation between release of K+ and this enzyme (r = 0.88). No lysis of platelets occurred, since lactic dehydrogenase was not detected. Pretreatment of platelets with aspirin in vitro inhibited thrombin-induced release of serotonin but had no effect on the loss of K+ or .beta.-glucuronidase. In contrast, the ingestion of aspirin by mouth inhibited the release of serotonin, .beta.-glucuronidase and K+ by thrombin. The K+ loss induced by thrombin was apparently primarily derived from release of .alpha.-granules and that these organelles contained about 20% of the total platelet K+ in a freely exchangeable and nonsequestered state.