Cytosolic Ionized Calcium Homeostasis in Platelets: An Abnormal Sensitivity to PAF‐Activation in Migraine

Abstract

SYNOPSIS Platelet cytosolic ionized calcium ([Ca i 2+ ]) was measured in aequorin‐loaded gel‐filtered platelets in the basel state and following stimulation with thrombin, collagen and platelet‐activating factor (PAF). 25 healthy controls, 20 interval migraine subjects and 26 acute ischemic stroke patients were studied. Compared to controls, the basal [Ca i 2+ ] was increased in migraineurs (p = 0.05) and after stimulation with PAF (p<0.03); thrombin‐ and collagen‐induced changes were similar to control. Compared to controls, basal [Ca i 2+ ] was increased in stroke patients (p<0.002); the increase in [Ca i 2+ ] after stimulation with thrombin (p<0.05), collagen (p<0.02) and PAF (p< 0.05) was also greater in stroke. Compared to migraineurs, [Ca i 2+ ] was further increased in stroke after stimulation with thrombin (p<0.002) and collagen (p<0.02); PAF‐induced changes were similar in stroke and migraine. The greater concentration of basal cytosolic ionized Ca 2+ in platelets of migraine sufferers was associated with a normal response to activation by thrombin and collagen suggesting the presence of platelet hyporesponsiveness to activation by these agents in migraine sufferers. Unlike ischemic stroke patients where there is a nonspecific increase in response to platelet stimulating agents, the platelets of migraine sufferers appear to be specifically sensitive to activation by PAF suggesting that altered sensitivity to this phospholipid may be a characteristic unique to migraine sufferers.