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 cytosolic calcium [Ca 2 ] + i and intracellular pH [pH]i in human and murine platelets. Rich-platelet suspensions from both species were loaded with Fura-2 (2 w M) or BCECF (0.75 w M) by incubation with their respective acetoxymethyl esters to measure cytosolic calcium [Ca 2+ ] i or intracellular pH [pH]i, respectively. Suspensions were challenged with increasing concentrations of Thr, from 0.1 to 10 IU/ml. Basal [Ca 2+ ] i in human platelets was 98 - 6 and 99.1 - 9 nM in rat platelets ( n =20). Thr increased \[Ca2+] i , EC 50 was 1.1 - 0.04 in human and 0.97 - 0.06 IU/ml in rat platelets ( n =7). Extracellular Mg 2+ (4 or 8 mM) abolished Thr response on [Ca 2+ ] i . [pH]i in human was 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 [Ca 2+ ] i and [pH]i was similar in both species, allowing for comparisons between human and murine platelets and to extrapolate results from an animal model to human pathology.