Increased Membrane‐Bound Calcium in Platelets of Hypertensive Patients

The fluorescent indicator chlortetracycline was used to estimate membrane-bound calcium in mild, untreated hypertensive patients (n=39) and normotensive controls (n=42). All participants were black. After incubation with chlortetracycline, platelet-rich plasma was centrifuged into a pellet and fluorescence was measured with a microspectrofluorometer. At an interval of 45 minutes mean fluorescence values were 11% higher in the hypertensive than in the normotensive group (567±95 vs. 512±100 counts/sec, p < 0.02). With both groups of participants combined, a correlation of borderline statistical significance was noted between diastolic blood pressure and chlortetracycline fluorescence (r=0.213,p=0.056). In parallel experiments, sodium and potassium concentrations were measured in red blood cells. Intracellular sodium was also significantly higher hi the hypertensive group (p < 0.01). These data indicate that the total cell burden of calcium is increased in the platelets of hypertensive individuals, possibly a result of abnormal cell metabolism of calcium, and further suggest that circulating platelets in hypertensive individuals may be hi a hyperaggregable state.