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Increased membrane-bound calcium in platelets of hypertensive patients
1Department of Medicine, Cook County Hospital, Chicago, IL 60612.
Insights
Hypertensive patients show higher levels of membrane-bound calcium in platelets compared to normotensive individuals. This suggests potential calcium metabolism abnormalities and hyperaggregable platelets in hypertension.
Area of Science:
- Cardiovascular Medicine
- Biochemistry
- Cell Biology
Background:
- Hypertension is a significant risk factor for cardiovascular disease.
- Abnormalities in cellular calcium handling have been implicated in hypertensive pathophysiology.
- Platelet function is crucial in hemostasis and thrombosis, and altered platelet calcium may impact cardiovascular health.
Purpose of the Study:
- To investigate differences in membrane-bound calcium levels in platelets between hypertensive and normotensive individuals.
- To explore the relationship between blood pressure and platelet calcium.
- To assess intracellular sodium concentrations in red blood cells as a parallel marker.
Main Methods:
- Utilized the fluorescent indicator chlortetracycline to quantify membrane-bound calcium in platelets.
- Measured fluorescence intensity using a microspectrofluorometer after platelet-rich plasma incubation and centrifugation.
- Analyzed intracellular sodium and potassium concentrations in red blood cells.
Main Results:
- Platelets from mild, untreated hypertensive patients exhibited significantly higher chlortetracycline fluorescence (11% increase) compared to normotensive controls (p < 0.02).
- A borderline significant correlation was observed between diastolic blood pressure and platelet calcium levels (r = 0.213, p = 0.056).
- Intracellular sodium levels were also significantly elevated in hypertensive individuals (p < 0.01).
Conclusions:
- Hypertensive individuals demonstrate an increased total calcium burden in their platelets.
- These findings suggest potential alterations in calcium cell metabolism and a possible hyperaggregable state of circulating platelets in hypertension.
- The elevated intracellular sodium further supports cellular ion dysregulation in hypertension.
Abstract:
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 less than 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 in the hypertensive group (p less than 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 in a hyperaggregable state.