Characterization of platelet cytoplasmic Ca2+ mobilization in patients with congenital cyclo-oxygenase deficiency and with defective platelet aggregation to A23187.

Abstract

Agonist-induced platelet cytoplasmic Ca2+ concentrations ([Ca2+]i) in patients with congenital cyclo-oxygenase deficiency (A) and with impaired aggregation to A23187 (B) were measured with aequorin in the presence or absence of extracellular Ca2+. The influence of TMB-8 or ONO3708 on agonist-induced [Ca2+]i in those platelets was also investigated. In Patient 1, there was a single aequorin luminescence peak in response to arachidonate, which was a thromboxane A2(TXA2) independent Ca2+ influx. The luminescence peak due to the formation of TXA2 was not detectable. The A23187-induced [Ca2+] i was decreased in the presence of extracellular Ca2+, but was within normal limits in the absence of extracellular Ca2+. A thrombin or STA2-induced elevation of [Ca2+] i was always within normal limits under any conditions. These results suggest that cyclo-oxygenase activity (CO activity) contributes to the A23187-induced Ca2+ influx, but does not contribute to the Ca2+ release from intracellular stores, and that the thrombin or STA2-induced Ca2+ influx and release do not depend on the CO activity. In Patient 2, the time lag from the addition of A23187 to the aequorin luminescence peak was found both in the presence and absence of extracellular Ca2+, which was more obvious in the latter. This A23187-induced elevation of [Ca2+] i disappeared after treatment of the platelets with TMB-8 in the absence of extracellular Ca2+, which is rarely seen in normal platelets. The most striking finding was that the thrombin-induced rise in [Ca2+] i in the absence of extracellular Ca2+ was not detectable. These findings might be closely related to abnormal platelet function in this patient.