title: Ca2+ mobilization in blood platelets as visualized by chlortetracycline fluorescence.
abstract: Binding of intracellular Ca2+ was measured in intact human blood platelets using the fluorescent Ca2+ probe, chlortetracycline, and a photon-counting microspectrofluorometer. Low doses of epinephrine, A23187, or prostaglandin endoperoxide analog U46619 induced a release of intraplatelet membrane-bound Ca2+. When platelet transmembrane Ca2+ flux was blocked by verapamil or ethylenediaminetetraacetic acid (EDTA), Ca2+ mobilization in response to epinephrine was inhibited, whereas A23187- or U46619-induced Ca2+ release was unchanged. When indomethacin was used to inhibit cyclo-oxygenase activity, Ca2+ mobilization in response to epinephrine or U46619 was partially blocked, whereas Ca2+ release in response to A23187 was unaltered. The relationship between platelet cyclic adenosine 3',5'-monophosphate (cAMP) and intraplatelet Ca2+ binding was also investigated. Prostaglandin E1 or prostacyclin was found to markedly elevate cAMP as well as enhance platelet Ca2+ binding. These effects were augmented by inhibition of phosphodiesterase activity using RO201724. The relationship between cAMP and Ca2+ binding was linear in the range of 10-60 pmoles cAmP/ml platelet-rich plasma. In addition the increase in cAMP stimulated by prostaglandin E1 or prostacyclin reduced the ability of epinephrine, A23187, or U46619 to induce intraplatelet Ca2+ mobilization.
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002751:Chlortetracycline; D000242:Cyclic AMP / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D013050:Spectrometry, Fluorescence
chemical_list: D011450:Prostaglandin Endoperoxides, Synthetic; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000242:Cyclic AMP; D002118:Calcium; D002751:Chlortetracycline; D004837:Epinephrine