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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.
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
August 1995,
Zhonghua yi xue za zhi,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
May 1991,
Prostaglandins, leukotrienes, and essential fatty acids,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
August 1984,
The Biochemical journal,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
June 1991,
Biochemical and biophysical research communications,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
January 1984,
Journal of receptor research,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
April 2000,
Annals of the New York Academy of Sciences,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
October 1992,
Scandinavian journal of clinical and laboratory investigation,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
April 1995,
The American journal of physiology,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
October 1991,
The Journal of biological chemistry,
W K Pollock, and
R A Armstrong, and
L J Brydon, and
R L Jones, and
D E MacIntyre
March 1994,
Nihon Jinzo Gakkai shi,
