PLATELET MICROPARTICLES AND CALCIUM HOMEOSTASIS IN ACUTE CORONARY ISCHEMIAS

Elevation of free cytoplasmic calcium is the common pathway of platele t activation, leading to shape change, shedding of platelet microparti cles (PMP), aggregation, and secretion of internal granules, including expression of CD62p on the surface, Platelet activation is well docum ented in unstable angina (UA) and acute myocardial infarction (MI). We investigated the following markers of platelet activation in 55 patie nts undergoing coronary angiography for suspected CAD: free cytoplasmi c calcium, [Ca2+](cyts) PMP, CD62p expression, and platelet/leukocyte (P/L) interaction. [Ca2+](cyt) was measured by Fluo-3 and the other me asurements were by flow cytometry, Patients were classified into three groups: unstable angina (UA, n = 11), recent myocardial infarction (M I, n = 11), and patient controls (CTL, n = 33). Blood was drawn before infusion of heparin through femoral lines at the time of catheterizat ion for assays. Results: (1) PMP values were significantly higher in b oth UA and MI than in CTL, P < 0.05. There was no difference between U A and MI, (2) P/L interaction was significantly elevated only in UA, P < 0.05, (3) CD62p expression on free platelets did not differ signifi cantly between any of the three groups, (4) The resting [Ca2+](cyt), t hrombin-induced Ca2+ influx, and release of Ca2+ from internal stores were all significantly higher in platelets from the combined patient g roup (UA + MI) than in the patient control group, P < 0.001 Conclusion s: Results on calcium hemostasis and PMP were significantly different in patients with acute coronary syndromes than those with stable angin a or no coronary ischemia; this may reflect underlying pathophysiology of acute coronary ischemia. P/L interaction was higher only in the UA group, suggesting a role of leukocytes in UA. (C) 1997 Wiley-Liss, In c.