Baseline and activated platelet cytoplasmic ionized calcium in acute ischemic stroke. Effect of aspirin.

We measured cytoplasmic ionized calcium concentrations [( Cai2+]) in aequorin-loaded gel-filtered platelets from 38 patients with acute occlusive stroke (12 treated with aspirin, 26 untreated) and 25 healthy controls. Compared with controls, baseline [Cai2+] was higher in untreated patients (p less than 0.002), maximal 36-72 hours after the onset of neurologic dysfunction (p less than 0.0001), in those patients with as well as those without major stroke risk factors. The increase in [Cai2+] after stimulation with 0.5 and 1.0 unit/ml thrombin (p less than 0.05), 2 and 4 micrograms/ml collagen (p less than 0.02), and 0.5 and 1.0 mM platelet activating factor (p less than 0.05) were also greater in untreated patients, but the profiles of these changes were parallel to those in controls. Even though the platelets of stroke patients are more sensitive to activation, they are functionally similar to those of controls. Aspirin treatment reduced baseline [Cai2+] as well as thrombin- and collagen-induced [Cai2+] changes. Platelet activating factor-induced increase in [Cai2+] was not altered by aspirin treatment. Our results suggest that the usefulness of aspirin in stroke is limited because aspirin does not suppress platelet responsiveness to all in vivo thrombogenic stimuli. Specific platelet activating factor antagonists may prove to be useful therapeutic agents in stroke.