Extracellular pH affects platelet aggregation associated with modulation of store-operated Ca(2+) entry.
The pH dependence of store-operated Ca(2+) influx (SOCI) into human platelets, as well as its physiological consequence, aggregation, was studied. In Ca(2+)-free medium, thapsigargin (1 microM) induced a small increase in intracellular free-Ca(2+) ([Ca(2+)](i)), which was not affected by changes in extracellular pH. The addition of Ca(2+) (0.5-3 mM) after Ca(2+) store depletion caused by thapsigargin resulted in concentration-dependent increases in [Ca(2+)](i) (SOCI), which were strongly inhibited by SKF-96365 (100 microM), an inhibitor of receptor-mediated Ca(2+) entry. SOCI was inhibited by acidosis (pH 6.9) and augmented by alkalosis (pH 7.9). The addition of Ca(2+) (0.5-3 mM) to platelets, which were kept in Ca(2+)-free medium, slightly but significantly increased [Ca(2+)](i). This Ca(2+) leak entry was also decreased and increased by extracellular acidosis (pH 6.9) and alkalosis (pH 7.9), respectively, but not affected by SKF-96365. Neither thapsigargin (1 microM) stimulation in Ca(2+)-free solution nor elevation of extracellular Ca(2+) alone was sufficient to induce platelet aggregation. In contrast, the addition of Ca(2+) (1 mM) to platelets activated by thapsigargin resulted in aggregation, which was markedly inhibited by SKF-96365 (100 microM). Platelet aggregation associated with SOCI was also inhibited by extracellular acidosis (pH 6.9) and augmented by extracellular alkalosis (pH 7.9). These results suggest that acidosis-induced inhibition, as well as alkalosis-induced promotion of platelet aggregation, involve pH effects on SOCI.
Marumo
M
M
Department of Hygiene and Preventive Medicine, School of Medicine, Yamagata University, Iida-Nishi 2-2-2, 990-9585, Yamagata, Japan.
Suehiro
A
A
Kakishita
E
E
Groschner
K
K
Wakabayashi
I
I
D001792:Blood Platelets / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D007093:Imidazoles; D019284:Thapsigargin; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium