CHANGES IN CA2-PRONE SPONTANEOUSLY HYPERTENSIVE RATS( MOBILIZATION INPLATELETS FROM STROKE)

Intracellular free Ca2+, [Ca2+] i, levels were measured in platelets f rom stroke-prone spontaneously hypertensive rats (SHRSP) and normotens ive Wistar-Kyoto rats (WKY) using fura-2AM. In the presence of extrace llular Ca2+ (1 mM), [Ca2+] i levels in unstimulated platelets of 2- an d 9-month-old SHRSP were both significantly higher than those of the a ge matched WKY. In the absence of extracellular Ca2+, the levels in pl atelets from 9-month-old SHRSP were also higher than any other groups examined. Receptor-linked Ca2+ influxes of old SHRSP were smaller when thrombin or collagen was given to the platelets. Phorbol 12-myristate 13-acetate (TPA) enhanced more prominently the Ca2+ influx into old S HRSP platelets than into old WKY platelets. These results strongly sug gest that the Ca2+ permeability across plasma membrane is increased in young as well as old SHRSP platelets, where the resting [Ca2+] i leve l is highly sustained because of an impaired Ca2+ uptake mechanism and possible enhancement of protein kinase C activity.