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PMID: 6234886 Published · ppublish English Journal Article Research Support, Non-U.S. Gov't

Thromboxane-induced phosphatidate formation in human platelets. Relationship to receptor occupancy and to changes in cytosolic free calcium.

The Biochemical journal ·Vol. 219 ·No. 3 ·1984-05-01 ·Pages 833-42

Pollock WK, Armstrong RA, Brydon LJ, Jones RL, MacIntyre DE

Abstract

The inter-relationships between receptor occupancy, inositol phospholipid metabolism and elevation of cytosolic free Ca2+ in thromboxane A2-induced human platelet activation were investigated by using the stable thromboxane A2 mimetic, 9,11-epoxymethanoprostaglandin H2, and the thromboxane A2 receptor antagonist, EPO45. 9,11-Epoxymethanoprostaglandin H2 stimulated platelet phosphatidylinositol metabolism as indicated by the rapid accumulation of [32P]phosphatidate and later accumulation of [32P]phosphatidylinositol in platelets pre-labelled with [32P]Pi. These effects of 9,11-epoxymethanoprostaglandin H2 were concentration-dependent and half-maximal [32P]phosphatidate formation occurred at an agonist concentration of 54 +/- 8 nM. With platelets labelled with the fluorescent Ca2+ indicator quin 2, resting cytosolic free Ca2+ was 86 +/- 12 nM. 9,11-Epoxymethanoprostaglandin H2 induced a rapid, concentration-dependent elevation of cytosolic free Ca2+ to a maximum of 300-700 nM. Half-maximal stimulation was observed at an agonist concentration of 80 +/- 23 nM. The thromboxane A2 receptor antagonist EPO45 selectively inhibited 9,11-epoxymethanoprostaglandin H2-induced [32P]phosphatidate formation and elevation of cytosolic free Ca2+, indicating that both events are sequelae of receptor occupancy. Human platelets contain a single class of stereospecific, saturable, high affinity (KD = 70 +/- 13 nM) binding sites for 9,11-epoxymethano[3H]prostaglandin H2. The concentration-response curve for receptor occupancy (9,11-epoxymethano-[3H]prostaglandin H2 binding) is similar to that for 9,11-epoxymethanoprostaglandin H2-induced [32P]phosphatidate formation and for elevation of cytosolic free Ca2+. These observations indicate that human platelet thromboxane A2 receptor occupation is closely linked to inositol phospholipid metabolism and to elevation of cytosolic free Ca2+. Both such events may be necessary for thromboxane A2-induced human platelet activation.

MeSH Terms
Blood Platelets/drug effects,metabolism Calcium/blood Cytosol/metabolism Dose-Response Relationship, Drug Humans In Vitro Techniques Phosphatidic Acids/blood Phospholipids/biosynthesis Platelet Aggregation/drug effects Prostaglandin Endoperoxides, Synthetic/pharmacology Prostaglandin H2 Prostaglandins H/pharmacology Prostaglandins, Synthetic/pharmacology Receptors, Prostaglandin/blood Receptors, Thromboxane Thromboxane A2/pharmacology Thromboxanes/pharmacology
Chemicals
Phosphatidic Acids Phospholipids Prostaglandin Endoperoxides, Synthetic Prostaglandins H Prostaglandins, Synthetic Receptors, Prostaglandin Receptors, Thromboxane Thromboxanes Prostaglandin H2 Thromboxane A2 EP 045 Calcium
Authors & Affiliations
5 authors, click to expand affiliations / ORCID
Pollock W K
Armstrong R A
Brydon L J
Jones R L
MacIntyre D E
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Article Info
Journal
The Biochemical journal
Abbr.
Biochem J
ISSN
0264-6021
DOI
10.1042/bj2190833
Published
1984-05-01
Pages
833-42
Language
English
Region
England
NLM ID
2984726R
PMCID
PMC1153551
Subset
IM
External Links
PubMed source DOI: 10.1042/bj2190833 PMC Full Text View journal details
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