title: Low concentrations of the stable prostaglandin endoperoxide U44069 stimulate shape change in quin2-loaded platelets without a measurable increase in [Ca2+]i.
abstract: Dose-response relationships for raised cytoplasmic free calcium concentration, [Ca2+]i, and shape change were measured simultaneously in quin2-loaded human platelets. With the calcium ionophore ionomycin the threshold [Ca2+]i for shape change was 300 nM with a maximal response at 800 nM. With 1 mM external Ca2+ the U44069 concentrations required to stimulate half-maximal shape change and an increase in [Ca2+]i were 2 and 41 nM, respectively. For PAF these values were 8.7 and 164 pg/ml, respectively. Low concentrations of U44069 and PAF evoked substantial shape change without any rise in [Ca2+]i. In the absence of external Ca2+, U44069 stimulated half-maximal shape change at 2 nM, and half-maximal elevation of [Ca2+]i at 69 nM: here, increased [Ca2+]i never reached the threshold [Ca2+]i for shape-change derived with ionomycin. These results suggest that some transduction mechanism other than elevated [Ca2+]i, as yet unidentified, can cause shape change.
mesh_terms: D000634:Aminoquinolines; D001792:Blood Platelets / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000097:blood*; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D010972:Platelet Activating Factor / Q000494:pharmacology; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence
chemical_list: D000634:Aminoquinolines; D005456:Fluorescent Dyes; D010972:Platelet Activating Factor; D011450:Prostaglandin Endoperoxides, Synthetic; D004533:Egtazic Acid; C028429:U 44069; C035739:Quin2; D002118:Calcium