title: Inhibition of Na+/H+ exchange reduces Ca2+ mobilization without affecting the initial cleavage of phosphatidylinositol 4,5-bisphosphate in thrombin-stimulated platelets.
abstract: Stimulation of human platelets increases cytoplasmic pH (pHi) 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 U/ml thrombin, whereas increasing pHi by NH4Cl enhanced the thrombin-induced increase in cytosolic free Ca2+. The effect of EIPA was bypassed after increasing pHi by moneasin. The thrombin-induced cleavage of phosphatidylinositol 4,5-bisphosphate (PIP2) was unaffected by treatments that blocked Na+/H+ exchange or increased pHi. 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.
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; D013917:Thrombin; D002118:Calcium; C039614:ethylisopropylamiloride