Use of [3h]trimetoquinol as a radioligand in human platelets

Interaction with putative endoperoxide/thromboxane A2 receptor sites

Chang Ho Ahn, Lane J. Wallace, Duane Miller, Dennis R. Feller

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

We have recently shown that trimetoquinol [1-(3,4,5-trimethoxy-benzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; Tmq]is a potent and stereoselective [R(+)-isomer > S(-)-isomer]antagonist of aggregation induced by thromboxane A2 and stable epoxymethano PGH2 analogues (U46619; U44069) in human platelets. The present study was undertaken to characterize the pharmacological specificity of binding site for racemic- [3h]TMQ in washed human platelets. Specific binding of [3h]TMQ determined by addition of 100 μM R(+)-TMQ, accounted for 12-26% of the total binding at 1.0 μM. Saturation data suggested two binding sites with apparent dissociation constants of 2.8 nM and 1.4 μM for the high and low affinity binding sites, respectively. Maximal binding densities (pmol/mg protein) were 2.3 and 42.9 for the respective high and low affinity sites. The optical isomers of TMQ, cis and transisomers of 13-azaprostanoic acid (13-APA), and U46619 inhibited [3h]TMQ-specific binding to the low affinity site. R(+)-TMQ was 32-fold more potent than S(-)-TMQ at inhibiting [3h]TMQ binding, and the stereoselective potency difference and concentrations needed to inhibit binding were similar to those required for inhibition of U46619induced platelet aggregation and serotonin secretion. Similarly, tans-13-APA was 90-fold more potent than cis-13-APA as a competitor of [3h]TMQ binding. U46619 also inhibited TMQ binding at concentrations (IC 50 = 0.4 μM) similar to those required for aggregation (EC50 = 0.16 μM) an secretion (EC 5o = 0.23 μM). At 1 μM, arachidonic acid inhibited [3h]TMQ binding 6y only 25%. Our studies indicate that [3h]TMQ interacts with specific binding sites with characteristics indicative of putative endoperoxide/thromboxane A2 receptors in human platelets.

Original languageEnglish (US)
Pages (from-to)387-399
Number of pages13
JournalThrombosis Research
Volume50
Issue number3
DOIs
StatePublished - May 1 1988
Externally publishedYes

Fingerprint

Tretoquinol
Prostaglandin H2 Receptors Thromboxane A2
15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid
Blood Platelets
Binding Sites
Prostaglandin H2
Thromboxane A2
Platelet Aggregation
Arachidonic Acid
Serotonin
Pharmacology
13-azaprostanoic acid
Proteins

All Science Journal Classification (ASJC) codes

  • Hematology

Cite this

Use of [3h]trimetoquinol as a radioligand in human platelets : Interaction with putative endoperoxide/thromboxane A2 receptor sites. / Ahn, Chang Ho; Wallace, Lane J.; Miller, Duane; Feller, Dennis R.

In: Thrombosis Research, Vol. 50, No. 3, 01.05.1988, p. 387-399.

Research output: Contribution to journalArticle

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abstract = "We have recently shown that trimetoquinol [1-(3,4,5-trimethoxy-benzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; Tmq]is a potent and stereoselective [R(+)-isomer > S(-)-isomer]antagonist of aggregation induced by thromboxane A2 and stable epoxymethano PGH2 analogues (U46619; U44069) in human platelets. The present study was undertaken to characterize the pharmacological specificity of binding site for racemic- [3h]TMQ in washed human platelets. Specific binding of [3h]TMQ determined by addition of 100 μM R(+)-TMQ, accounted for 12-26{\%} of the total binding at 1.0 μM. Saturation data suggested two binding sites with apparent dissociation constants of 2.8 nM and 1.4 μM for the high and low affinity binding sites, respectively. Maximal binding densities (pmol/mg protein) were 2.3 and 42.9 for the respective high and low affinity sites. The optical isomers of TMQ, cis and transisomers of 13-azaprostanoic acid (13-APA), and U46619 inhibited [3h]TMQ-specific binding to the low affinity site. R(+)-TMQ was 32-fold more potent than S(-)-TMQ at inhibiting [3h]TMQ binding, and the stereoselective potency difference and concentrations needed to inhibit binding were similar to those required for inhibition of U46619induced platelet aggregation and serotonin secretion. Similarly, tans-13-APA was 90-fold more potent than cis-13-APA as a competitor of [3h]TMQ binding. U46619 also inhibited TMQ binding at concentrations (IC 50 = 0.4 μM) similar to those required for aggregation (EC50 = 0.16 μM) an secretion (EC 5o = 0.23 μM). At 1 μM, arachidonic acid inhibited [3h]TMQ binding 6y only 25{\%}. Our studies indicate that [3h]TMQ interacts with specific binding sites with characteristics indicative of putative endoperoxide/thromboxane A2 receptors in human platelets.",
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AU - Feller, Dennis R.

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N2 - We have recently shown that trimetoquinol [1-(3,4,5-trimethoxy-benzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; Tmq]is a potent and stereoselective [R(+)-isomer > S(-)-isomer]antagonist of aggregation induced by thromboxane A2 and stable epoxymethano PGH2 analogues (U46619; U44069) in human platelets. The present study was undertaken to characterize the pharmacological specificity of binding site for racemic- [3h]TMQ in washed human platelets. Specific binding of [3h]TMQ determined by addition of 100 μM R(+)-TMQ, accounted for 12-26% of the total binding at 1.0 μM. Saturation data suggested two binding sites with apparent dissociation constants of 2.8 nM and 1.4 μM for the high and low affinity binding sites, respectively. Maximal binding densities (pmol/mg protein) were 2.3 and 42.9 for the respective high and low affinity sites. The optical isomers of TMQ, cis and transisomers of 13-azaprostanoic acid (13-APA), and U46619 inhibited [3h]TMQ-specific binding to the low affinity site. R(+)-TMQ was 32-fold more potent than S(-)-TMQ at inhibiting [3h]TMQ binding, and the stereoselective potency difference and concentrations needed to inhibit binding were similar to those required for inhibition of U46619induced platelet aggregation and serotonin secretion. Similarly, tans-13-APA was 90-fold more potent than cis-13-APA as a competitor of [3h]TMQ binding. U46619 also inhibited TMQ binding at concentrations (IC 50 = 0.4 μM) similar to those required for aggregation (EC50 = 0.16 μM) an secretion (EC 5o = 0.23 μM). At 1 μM, arachidonic acid inhibited [3h]TMQ binding 6y only 25%. Our studies indicate that [3h]TMQ interacts with specific binding sites with characteristics indicative of putative endoperoxide/thromboxane A2 receptors in human platelets.

AB - We have recently shown that trimetoquinol [1-(3,4,5-trimethoxy-benzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; Tmq]is a potent and stereoselective [R(+)-isomer > S(-)-isomer]antagonist of aggregation induced by thromboxane A2 and stable epoxymethano PGH2 analogues (U46619; U44069) in human platelets. The present study was undertaken to characterize the pharmacological specificity of binding site for racemic- [3h]TMQ in washed human platelets. Specific binding of [3h]TMQ determined by addition of 100 μM R(+)-TMQ, accounted for 12-26% of the total binding at 1.0 μM. Saturation data suggested two binding sites with apparent dissociation constants of 2.8 nM and 1.4 μM for the high and low affinity binding sites, respectively. Maximal binding densities (pmol/mg protein) were 2.3 and 42.9 for the respective high and low affinity sites. The optical isomers of TMQ, cis and transisomers of 13-azaprostanoic acid (13-APA), and U46619 inhibited [3h]TMQ-specific binding to the low affinity site. R(+)-TMQ was 32-fold more potent than S(-)-TMQ at inhibiting [3h]TMQ binding, and the stereoselective potency difference and concentrations needed to inhibit binding were similar to those required for inhibition of U46619induced platelet aggregation and serotonin secretion. Similarly, tans-13-APA was 90-fold more potent than cis-13-APA as a competitor of [3h]TMQ binding. U46619 also inhibited TMQ binding at concentrations (IC 50 = 0.4 μM) similar to those required for aggregation (EC50 = 0.16 μM) an secretion (EC 5o = 0.23 μM). At 1 μM, arachidonic acid inhibited [3h]TMQ binding 6y only 25%. Our studies indicate that [3h]TMQ interacts with specific binding sites with characteristics indicative of putative endoperoxide/thromboxane A2 receptors in human platelets.

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