Inhibition of Na+/H+ exchange reduces Ca2+ mobilization without affecting the initial cleavage of phosphatidylinositol 4,5‐bisphosphate in thrombin‐stimulated platelets

[摘要]

Stimulation of human platelets increases cytoplasmic pH (pH_i) via activation of Na⁺/H⁺ exchange. We have determined the effect of inhibiting Na⁺/H⁺ exchange on (i) thrombin-induced Ca²⁺ mobilization and (ii) turnover of ³²P-labelled phospholipids. Blocking Na⁺/H⁺ exchange by removal of extracellular Na⁺ or by ethylisopropylamiloride (EIPA) inhibited Ca²⁺ mobilization induced by 0.2 thrombin, whereas increasing pH_i by NH₄C1 enhanced the thrombin-induced increase in cytosolic free Ca²⁺. The effect of EIPA was bypassed after increasing pH_i by moneasin. The thrombin-induced cleavage of phosphatidylinositol 4,5-bisphosphate (PIP₂) was unaffected by treatments that blocked Na⁺/H⁺ exchange or increased pH_i. It is concluded that activation of Na⁺/H⁺ exchange is a prerequisite for Ca²⁺ mobilization in human platelets but not for the stimulus-induced hydrolysis of PIP₂.

[学科分类] 生物化学/生物物理

[关键词] Na+/H+ exchange;Amiloride;Phosphoinositide;Quin 2;Ca2+ mobilization;Platelet activation;[Ca2+]i;cytosolic free Ca2+ concentration;Cao 2+;external Ca2+;Nao +;external Na+;IP3;inositol 1;4;5-trisphosphate;PIP2;phosphatidylinositol 4;5-bisphosphate;PIP;phosphatidylinositol 4-phosphate;PI;phosphatidylinositol;PA;phosphatidic acid;EIPA;ethylisopropylamiloride