Two classes of agonist-sensitive Ca2+ stores in platelets, as identified by their differential sensitivity to 2,5-di-(tert-butyl)-1,4-benzohydroquinone and thapsigargin

In the absence of extracellular Ca2+, extensive Ca2+ release from the platelet intracellular stores [monitored as an increase of intracellular Ca2+ concentration ([Ca2+]i)] is produced by the combined action of the endomembrane Ca(2+)-ATPase inhibitor thapsigargin and 2 nM ionomycin. The titration o...

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Bibliographic Details
Published in:Biochemical journal 1995-09, Vol.310 ( Pt 2) (2), p.449-452
Main Authors: Cavallini, L, Coassin, M, Alexandre, A
Format: Article
Language:English
Subjects:
Antioxidants - pharmacology
Blood Platelets - drug effects
Blood Platelets - metabolism
Calcium - blood
Calcium-Transporting ATPases - antagonists & inhibitors
Cytosol - metabolism
Dose-Response Relationship, Drug
Humans
Hydroquinones - pharmacology
In Vitro Techniques
Ionomycin - pharmacology
Kinetics
Terpenes - pharmacology
Thapsigargin
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Summary:In the absence of extracellular Ca2+, extensive Ca2+ release from the platelet intracellular stores [monitored as an increase of intracellular Ca2+ concentration ([Ca2+]i)] is produced by the combined action of the endomembrane Ca(2+)-ATPase inhibitor thapsigargin and 2 nM ionomycin. The titration of Ca2+ unloading with thapsigargin (plus ionomycin) shows that a substantial fraction of the store-associated Ca2+ is released by 8-10 nM thapsigargin, but that 100-200 nM thapsigargin is required for the complete release. The store depletion obtained in similar conditions with a different endomembrane Ca(2+)-ATPase inhibitor, 2,5-di-(tert-butyl)-1,4-benzohydroquinone (TBHQ), is always incomplete. It is completed by thrombin or by 10 nM thapsigargin. We conclude that two different types of Ca2+ pumps exist in platelets, one sensitive to TBHQ and to high thapsigargin, the other insensitive to TBHQ and sensitive to low thapsigargin. They are distributed separately in discrete subpopulations of the agonist-sensitive stores. The influx of external Ca2+ is maximal when both types of stores are Ca(2+)-depleted, either by high thapsigargin or by the combined action of low thapsigargin and TBHQ.
ISSN:0264-6021
1470-8728
DOI:10.1042/bj3100449