Platelet hyperactivity and abnormal Ca(2+) homeostasis in diabetes mellitus.
We sought to determine the mechanisms for hyperactivity and abnormal platelet Ca(2+) homeostasis in diabetes. The glycosylated Hb (HbA(1c)) level was used as an index of glycemic control. Human platelets were loaded with Ca- green-fura red, and cytosolic Ca(2+) ([Ca(2+)](i)) and aggregation were simultaneously measured. In the first series of experiments, the platelets from diabetic and normal subjects were compared for the ability to release Ca(2+) or to promote Ca(2+) influx. A potent and relatively specific inhibitor of Na(+)/Ca(2+) exchange, 5-(4-chlorobenzyl)-2',4'-dimethylbenzamil (CB-DMB), increased the second phase of thrombin-induced Ca(2+) response, suggesting that the Na(+)/Ca(2+) exchanger works in the forward mode to mediate Ca(2+) efflux. In contrast, in the platelets from diabetics, CB-DMB decreased the Ca(2+) response, indicating that the Na(+)/Ca(2+) exchanger works in the reverse mode to mediate Ca(2+) influx. In the second series of experiments we evaluated the direct effect of hyperglycemia on platelets in vitro. We found that thrombin- and collagen-induced increases in [Ca(2+)](i) and aggregation were not acutely affected by high glucose concentrations of 45 mM. However, when the platelet-rich plasma was incubated with a high glucose concentration at 37 degrees C for 24 h, the second phase after thrombin activation was inhibited by CB-DMB. In addition, collagen-stimulated [Ca(2+)](i) response and aggregation were also increased. Thus in diabetes the direction and activity of the Na(+)/Ca(2+) exchanger is changed, which may be one of the mechanisms for the increased platelet [Ca(2+)](i) and hyperactivity. Prolonged hyperglycemia in vitro can induce similar changes, suggesting hyperglycemia per se may be the factor responsible for the platelet hyperactivity in diabetes.
Li
Y
Y
Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg R3E OW3, Canada.
Woo
V
V
Bose
R
R
D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D001786:Blood Glucose / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000097:blood*; D003094:Collagen / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D003920:Diabetes Mellitus / Q000097:blood / Q000503:physiopathology*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000503:physiopathology; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000503:physiopathology; D006706:Homeostasis; D006801:Humans; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D010974:Platelet Aggregation; D012016:Reference Values; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000097:blood; D013917:Thrombin / Q000494:pharmacology
D001786:Blood Glucose; D019831:Sodium-Calcium Exchanger; C054391:5-(N-4-chlorobenzyl)-N-(2',4'-dimethyl)benzamil; D015759:Ionomycin; D000584:Amiloride; D003094:Collagen; D013917:Thrombin; D002118:Calcium