Age-associated Changes in Intracellular Ca(2+) Mobilization and Basal pH Level in Rat Platelets

[Ca(2+)](i) and pH(i) were measured in unstimulated and thrombin-stimulated platelets from young (3 months) and aged (24 months) rats in the presence and absence of external Ca(2+). There was no difference in the basal level of [Ca(2+)](i) between young and aged rat platelets in the presence of external Ca(2+). On the other hand, thrombin-induced Ca(2+) mobilization was markedly increased in aged rat platelets compared to young rat platelets in the presence of external Ca(2+). This difference in Ca(2+) mobilization was more pronounced in the absence of external Ca(2+), suggesting that Ca(2+) release from intracellular storages was enhanced in aged rat platelets. In contrast to what was observed for Ca(2+), the basal level of pH(i) in aged rat platelets was higher than that in young rat platelets whereas thrombin-induced pH(i) increases (ΔpH) were similar in both groups in the presence and absence of external Ca(2+). These results indicate that age-associated changes occur in thrombin-induced Ca(2+) release from intracellular storages in rat platelets. These changes seem to be related to those in basal pH(i) levels.