Mobilization of intracellular Ca2+ modulates activation of Na+/H+ exchange in thrombin-stimulated platelets.

AIM: To study the relationship between intracellular calcium translocation and activation of Na+/H+ exchange in thrombin-stimulated platelets. METHODS: Intracellular Ca2+ ([Ca2+]i) and pH (pHi) were measured by a dual wavelength fluorophotometer with Fura-2 and pH-sensitive probe BCECF. RESULTS: Thrombin 0.1 IU.L-1 elicited an increase in platelet [Ca2+]i and pHi, the maximal increase in [Ca2+]i occurred earlier than the rise in pHi. In Na(+)-free buffers, the Na+/H+ exchange was markedly suppressed without affecting the elevation of [Ca2+]i; while intracellular acidification with nigericin 1 mg.L-1 inhibited the increment of [Ca2+]i. Blockade of Ca(2+)-influx with egtazic acid (EGTA) did not affect cytosolic alkalinization. Depletion of intracellular Ca2+ store with ionomycin in the presence of EGTA, no increment in pHi was observed, the basal value of pHi was even more acidic, this response of pHi to thrombin was rehabilitated after refilling of intracellular Ca2+ store with extracellular Ca2+ 1 mmol.L-1. CONCLUSION: Intracellular Ca2+ mobilization modulated activation of Na+/H+ exchange, which required an effective increment of [Ca2+]i.