MOBILIZATION OF INTRACELLULAR CA2+ MODULATES ACTIVATION OF NA+ H+ EXCHANGE IN THROMBIN-STIMULATED PLATELETS/

AIM: To study the relationship between intracellular calcium transloca tion and activation of Na+/H+ exchange in thrombin-stimulated platelet s. METHODS: Intracellular Ca2+ ([Ca2+](i)) and pH (pH(i)) were measure d by a dual wavelength fluorophotometer with Fura-2 and pH-sensitive p robe BCECF. RESULTS: Thrombin 0.1 IU . L-1 elicited an increase in pla telet [Ca2+](i) and pH(i), the maximal increase in [Ca2+](i) occurred earlier than the rise in pH(i). In Na+-free buffers, the Na+/H+ exchan ge was markedly suppressed without affecting the elevation of [Ca2+](i ); while intracellular acidification with nigericin 1 mg . L-1 inhibit ed the increment of [Ca2+](i). Blockade of Ca2+-influx with egtazic ac id (EGTA) did not affect cytosolic alkalinization. Depletion of intrac ellular Ca2+ store with ionomycin in the presence of EGTA, no incremen t in pH(i) was observed, the basal value of pH(i) was even more acidic , this response of pH(i) to thrombin was rehabilitated after refilling of intracellular Ca2+ store with extracellular Ca2+ 1 mmol . L-1. CON CLUSION: Intracellular Ca2+ mobilization modulated activation of Na+/H + exchange, which required an effective increment of [Ca2+](i).