Platelet calcium homeostasis is abnormal in patients with severe arteriosclerosis

To evaluate platelet calcium homeostasis in a typical thrombosis-prone clinical condition, 14 patients with severe arteriosclerosis and 11 healthy control subjects were studied. Platelet intracellular free calcium concentration ([Ca²⁺]_i) was evaluated by means of the fluorescent probe fura 2 under resting conditions and after challenge with 0.05, 0.1, and 0.5 U/mL thrombin (final concentrations). Three different concentrations of extracellular ionized calcium ([Ca²⁺]_e) were used: 1 mmol/L, 1 μmol/L, and <1 nmol/L. Resting platelet [Ca²⁺]_i was significantly higher (P<.001) in patients than in control subjects. After addition of 0.05 U/mL thrombin, the relative increase of [Ca²⁺]_i was lower in patients than in control subjects in each of the three [Ca²⁺]_i conditions (P=.05 at 1 mmol/L, P=.02 at 1 μmol/L, and P=.04 at <1 nmol/L). After addition of 0.1 U/mL thrombin, the relative increase of [Ca²⁺], was lower in patients than in control subjects under two [Ca²⁺]_c conditions, 1 μmol/L and <1 nmol/L (P=.04 and P=.03, respectively). With 0.5 U/mL thrombin, a trend toward lower values in patients than in control subjects was observed, reaching statistical significance (P=.03) only at <1 nmol/L [Ca²⁺]_c. These results suggest that calcium homeostasis is abnormal in platelets from patients with severe arteriosclerosis and probably reflects a chronic activation.