Effects of thrombin on intracellular calcium and pH in human and murine platelets

The aim of this study was to compare the effect of thrombin (Thr) on cytoso lic calcium [Ca2+](i) and intracellular pH [pH]i in human and murine platel ets, Rich-platelet suspensions from both species were loaded with Fura-2 (2 mu M) or BCECF (0.75 mu M) by incubation with their respective acetoxymeth yl esters to measure cytosolic calcium [Ca2+](i) or intracellular pH [pH]i, respectively. Suspensions were challenged with increasing concentrations o f Thr, from 0.1 to 10 IU/ml, Basal [Ca2+](i) in human platelets was 98+/-6 and 99.1+/-9 nM in rat platelets (n=20). Thr increased [Ca2+](i), EC50 was 1.1+/-0.04 in human and 0.97+/-0.06 IU/ml in rat platelets (n=7). Extracell ular Mg2+ (4 or 8 mM) abolished Thr response on [Ca2+](i). [pH]i in human w as 7.09+/-0.08 and 7.11+/-0.04 in rat platelets. Thr induced alkalinization of platelets in both species, Our results indicate that the potency of Thr to change [Ca2+](i) and [pH]i was similar in both species, allowing for co mparisons between human and murine platelets and to extrapolate results fro m an animal model to human pathology.