人体血小板中钠-氢离子与锂-氢离子交换的比较。

Comparison between sodium-hydrogen ion and lithium-hydrogen ion exchange in human platelets.

作者信息

Gende O A, Cingolani H E

机构信息

Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina.

出版信息

Biochim Biophys Acta. 1993 Nov 7;1152(2):219-24. doi: 10.1016/0005-2736(93)90252-u.

DOI:10.1016/0005-2736(93)90252-u

PMID:8218322

Abstract

The membrane-coupled exchange of Li+ and/or Na+ for H+ was studied in human platelets measuring intracellular pH(pHi) with a fluorescent indicator. A Li(+)-containing medium restored the internal pH of preacidified platelets to their prior pHi control value. When Na+ was replaced by Li+, similar steady-state values were attained in this system, although it was transported more slowly. The Km and Vmax were both higher with Na+ than with Li+. Exchanges of Li+ or Na+ with H+ were both blocked by ethylisopropylamiloride (EIPA) achieving half-maximal inhibition at submicromolar concentrations. The efflux Li+ or Na+ and resuspended in a choline medium exhibited an influx of H+ sensitive to EIPA. Thrombin, an activator of Na+/H+ exchange, induced a rapid increase in platelet internal pH in the presence of exogenous Li+. Thus: (1) Li+ can be substituted for Na+ in both the forward and the reverse exchange reaction; (2) Li+, while having a higher affinity than Na+ for the external site of the membrane carrier, has a lower Km and (3) Li+ as well as Na+ exchange are activated by thrombin.

摘要

利用荧光指示剂测量细胞内pH值（pHi），对人血小板中Li⁺和/或Na⁺与H⁺的膜偶联交换进行了研究。含Li⁺的培养基可将预酸化血小板的内部pH值恢复到其先前的pHi对照值。当用Li⁺替代Na⁺时，该系统达到了相似的稳态值，尽管其转运速度较慢。Na⁺时的Km和Vmax均高于Li⁺时。Li⁺或Na⁺与H⁺的交换均被乙基异丙基氨氯吡咪（EIPA）阻断，在亚微摩尔浓度下达到半数最大抑制。流出Li⁺或Na⁺并重悬于胆碱培养基中的血小板表现出对EIPA敏感的H⁺流入。凝血酶是Na⁺/H⁺交换的激活剂，在存在外源性Li⁺的情况下可诱导血小板内部pH值迅速升高。因此：（1）在正向和反向交换反应中Li⁺均可替代Na⁺；（2）Li⁺虽然对膜载体的外部位点的亲和力高于Na⁺，但其Km较低；（3）Li⁺以及Na⁺交换均被凝血酶激活。