Intracellular alkalinization augments platelet aggregation due to increase in cytosolic free-Ca2+.
Intracellular pH is known to increase during agonist-induced platelet activation. In order to elucidate the role of intracellular alkalinization in platelet activation, the effects of NH4Cl, as a tool to induce intracellular alkalinization, on ionomycin-induced platelet activation were investigated. NH4Cl (2.5-10 mM) concentration-dependently induced intracellular alkalinization. Platelet aggregation induced by ionomycin (0.1 microM) was augmented by treatment with NH4Cl (2.5-10 mM). Ionomycin-induced platelet aggregation in the absence of extraplatelet Ca2+, which was markedly attenuated compared to that in the presence of extraplatelet Ca2+, was also augmented by NH4Cl. NH4Cl treatment increased the number of large aggregates after ionomycin stimulation, while it decreased the number of small aggregates. Both transplasmalemmal Ca2+ entry and intracellular Ca2+ release induced by ionomycin were increased by treatment with NH4Cl (10 mM). SKF-96365 (100 microM), an inhibitor of receptor-operated Ca2+ channels, did not affect ionomycin-induced Ca2+ entry but abolished the effect of NH4Cl on Ca2+ entry. Thus, NH4Cl augments receptor-operated Ca2+ channels and intracellular Ca2+ release. These findings suggest that intracellular alkalinization plays a significant role in agonist-induced platelet activation.
Department of Hygiene and Preventive Medicine, School of Medicine, Yamagata University, Japan.
Mikio
M
Marumo
Akira
A
Suehiro
Eizo
E
Kakishita
Ichiro
I
Wakabayashi
D000643:Ammonium Chloride / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin; D007700:Kinetics; D009391:Nephelometry and Turbidimetry; D010974:Platelet Aggregation / Q000187:drug effects
D000643:Ammonium Chloride; D015759:Ionomycin; D002118:Calcium