Mobilization of intracellular Ca^(2+) modulates activation of Na^+/H^+ exchange in thrombin-stimulated platelets

目的：研究凝血酶诱导的血小板活化中细胞内钙动员和Ｎａ＋／Ｈ＋交换的关系．方法：Ｆｕｒａ２负载测［Ｃａ２＋］ｉ和ＢＣＥＣＦ负载测ｐＨｉ．结果：凝血酶０１ＩＵ·Ｌ－１引起［Ｃａ２＋］ｉ和ｐＨｉ增加，［Ｃａ２＋］ｉ增加先于ｐＨｉ增加．在无钠溶液中，Ｎａ＋／Ｈ＋交换被抑制而［Ｃａ２＋］ｉ增加不受影响；用尼日利亚菌素（１ｍｇ·Ｌ－１）使胞内酸化可抑制［Ｃａ２＋］ｉ增加．用依他酸（ＥＧＴＡ）阻断外钙内流，胞浆碱化不受影响．伊屋诺霉素加ＥＧＴＡ耗竭胞内钙池时，胞浆硷化效应被取消，且静息ｐＨｉ更低，加入１ｍｍｏｌ·Ｌ－１外钙重新充填钙池，胞浆碱化效应又被恢复．结论：细胞内钙动员调控Ｎａ＋／Ｈ＋交换，后者需［Ｃａ２＋］ｉ增加达一定有效浓度．

AIM: To study the relationship between intracellular calcium translocation and activation of Na^+/H`+ exchange in thrombin stimulated platelets. METHODS: Intracellular Ca^2+ ([Ca^2+ ] i) and pH (pH i) 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 [Ca 2+ ] i and pH i, the maximal increase in [Ca 2+ ] i occurred earlier than the rise in pH i. In Na + free buffers, the Na +/H + exchange was markedly suppressed without affecting the elevation of [Ca 2+ ] i; while intracellular acidification with nigericin 1 mg·L -1 inhibited the increment of [Ca 2+ ] i. Blockade of Ca 2+ influx with egtazic acid (EGTA) did not affect cytosolic alkalinization. Depletion of intracellular Ca 2+ store with ionomycin in the presence of EGTA, no increment 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 Ca 2+ store with extracellular Ca 2+ 1 mmol·L -1 . CONCLUSION: Intracellular Ca 2+ mobilization modulated activation of Na +/H + exchange, which required an effective increment of [Ca 2+ ] i.