细胞外钠离子而非钠氢交换，是血小板中受体介导的花生四烯酸释放所必需的。

Extracellular Na+, but not Na+/H+ exchange, is necessary for receptor-mediated arachidonate release in platelets.

作者信息

Krishnamurthi S, Morgan W A, Kakkar V V

机构信息

Thrombosis Research Unit, Rayne Institute, King's College School of Medicine and Dentistry, London, U.K.

出版信息

Biochem J. 1990 Jan 1;265(1):155-60. doi: 10.1042/bj2650155.

DOI:10.1042/bj2650155

PMID:2154180

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1136625/

Abstract

The effect of extracellular Na+ removal and replacement with other cations on receptor-mediated arachidonate release in platelets was studied to investigate the role of Na+/H+ exchange in this process. Replacement with choline+, K+, N-methylglucamine+ (which abolished the thrombin-induced pHi rise) or Li+ (which allowed a normal thrombin-induced pHi rise) significantly decreased arachidonate release in response to all concentrations (threshold to supra-maximal) of thrombin and collagen. This inhibition was not reversed by NH4Cl (10 mM) addition, which raised the pHi in the absence of Na+, but, on the contrary, NH4Cl addition further decreased the extent of thrombin- and collagen-induced arachidonate release, as well as decreasing 'weak'-agonist (ADP, adrenaline)-induced release and granule secretion in platelet-rich plasma. No detectable pHi rises were seen with collagen (1-20 micrograms/ml) and ADP (10 microM) in bis-(carboxyethyl)carboxyfluorescein-loaded platelets. Inhibition of thrombin-induced pHi rises was seen with 0.5-5 microM-5-NN-ethylisopropylamiloride (EIPA), but at these concentrations EIPA had little effect on thrombin-induced arachidonate release. At higher concentrations such as those used in previous studies (20-50 microM), EIPA inhibited aggregation/release induced by collagen and ADP in Na+ buffer as well as in choline+ buffer (where there was no detectable exchanger activity), suggesting that these concentrations of EIPA exert 'non-specific' effects at the membrane level. The results suggest that (i) Na+/H+ exchange and pHi elevations are not only necessary, but are probably inhibitory, to receptor-mediated arachidonate release in platelets, (ii) inhibition of receptor-mediated release in the absence of Na+ is most likely due to the absent Na+ ion itself, and (iii) caution should be exercised in the use of compounds such as EIPA, which, apart from inhibiting the Na+/H+ exchanger, have other undesirable and misleading effects in platelets.

摘要

研究了细胞外Na⁺去除并用其他阳离子替代对血小板中受体介导的花生四烯酸释放的影响，以探讨Na⁺/H⁺交换在此过程中的作用。用胆碱⁺、K⁺、N - 甲基葡糖胺⁺（可消除凝血酶诱导的细胞内pH值升高）或Li⁺（可使凝血酶诱导的细胞内pH值正常升高）替代，可显著降低对所有浓度（阈值至超最大浓度）的凝血酶和胶原的花生四烯酸释放。加入10 mM NH₄Cl（可在无Na⁺时升高细胞内pH值）并不能逆转这种抑制作用，相反，加入NH₄Cl进一步降低了凝血酶和胶原诱导的花生四烯酸释放程度，同时也降低了富含血小板血浆中“弱”激动剂（ADP、肾上腺素）诱导的释放和颗粒分泌。在用双（羧乙基）羧基荧光素负载的血小板中，1 - 20微克/毫升的胶原和10微摩尔的ADP未检测到细胞内pH值升高。0.5 - 5微摩尔的5 - NN - 乙基异丙基amiloride（EIPA）可抑制凝血酶诱导的细胞内pH值升高，但在这些浓度下EIPA对凝血酶诱导的花生四烯酸释放影响很小。在更高浓度下，如先前研究中使用的浓度（20 - 50微摩尔），EIPA在Na⁺缓冲液以及胆碱⁺缓冲液（其中未检测到交换体活性）中均抑制胶原和ADP诱导的聚集/释放，这表明这些浓度的EIPA在膜水平发挥“非特异性”作用。结果表明：（i）Na⁺/H⁺交换和细胞内pH值升高不仅是血小板中受体介导的花生四烯酸释放所必需的，而且可能具有抑制作用；（ii）在无Na⁺时受体介导的释放受到抑制很可能是由于Na⁺离子本身的缺失；（iii）在使用诸如EIPA等化合物时应谨慎，因为这些化合物除了抑制Na⁺/H⁺交换体外，在血小板中还具有其他不良和误导性作用。