IMPAIRED MOBILIZATION OF INTRACELLULAR CALCIUM IN NEONATAL PLATELETS

Abnormalities in platelet functions including aggregation and the rele ase reaction have long been recognized to be present in neonatal plate lets. Because calcium is an important mediator of many platelet functi ons, we have investigated the mobilization of calcium in neonatal plat elets. All umbilical cord blood samples were obtained from healthy, fu ll term gestations. Changes in cytoplasmic calcium levels were monitor ed using Fura-2 as a fluorescent probe. Fura-2-loaded washed platelets were stimulated with the agonists collagen (2 mu g/mL) or thrombin (1 .0 U/mL). When compared with adult controls, intracellular calcium rel ease in the platelets of the neonate was significantly impaired in res ponse to these agonists. Mean levels for calcium release in adults ver sus neonates in response to collagen were 168 +/- 120 nM (+/-SD, n = 1 0), and 61 +/- 69 nM (n = 7, p < 0.05). A decrease in response to thro mbin was also observed [1296 +/- 503 nM (n = 8) in adults versus 603 /- 482 nM (n = 7) in neonates, p < 0.025]. Results similar to those ob served with unpaired neonatal and adult platelets were also obtained w hen neonatal platelets (n = 5) were compared with their paired materna l controls. In further studies, we have documented that the calcium co ntent of the dense tubular system was normal in the neonatal platelet, indicating that the observed impairment in calcium mobilization in th e neonate was not due to a decrease in calcium stores. The previously documented abnormalities in neonatal platelet function appear to be du e to the impaired mobilization of this important intracellular mediato r.