Abnormal platelet Ca2+handling accompanied by increased cytosolic free Mg2+ in essential hypertension.

To test the hypothesis that abnormal platelet Ca2+ handling in essential hypertension results from cellular Mg2+ deficiency, cytosolic free Mg2+ concentration ([Mg2+]i) and Ca2+ metabolism were studied in mag-fura 2 and fura 2-loaded platelets from 30 essential hypertensive patients and 30 sex- and age-matched normotensive controls. Basal cytosolic free Ca2+ concentration ([Ca2+]i) and intracellular Ca2+ discharge capacity were higher in hypertensives than in normotensives (22 ± 5 vs. 18 ± 5 nM, P < 0.05; 743 ± 250 vs. 624 ± 144 nM, P < 0.05, respectively). The thrombin (0.03-1.0 U/ml)-evoked [Ca2+]iresponse was also enhanced in platelets from hypertensives in both the absence and presence of extracellular Ca2+. However, basal [Mg2+]iwas higher in hypertensives than in normotensives (437 ± 110 vs. 353 ± 85 μM, P < 0.05), whereas serum Mg2+ was similar in the two groups. These results oppose the Mg2+ deficiency hypothesis in platelets in essential hypertension.