| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1986: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1985: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
The metabolism of inositol phospholipids in response to 5HT was investigated in human platelets using the sensitive radioisotopicmethod of Berridge (1983), since it is well-known that ketanserin antagonizes 5HT-induced shape change and rise of intracellular free Ca ion. In platelets prelabeled with <^3H> -myo inositol, in Ca ion free HEPES buffer containing 10mM Licl and l <micro> M fluoxetine, 5HT caused a dose-dependent accumulation of inositol-l-phosphate(IP-l) during 15 min incubation. A maximal increase in IP-l formation was observed at 30 <micro> M of 5HT and its <EC_(50)> value was 4 <micro> M. Ketanserin, a selective 5HT-2 antagonist, was a potent inhibitor of 5HT-stimulated IP-l accumulation with a Ki value of 12nM, but a selective 5HT-l antagonist, (-)-propranolol(l <micro> M), failed to block the 5HT response. Metergoline, a mixed 5HT-l and 5HT-2 antagonist, caused almost the same reduction in 5HT-stimulated IP-l formation, with a Ki value of 5nM, as ketanserin. These results indicate that 5HT is activating 5HT-2,but not 5HT-l receptors in human platelets. Moreover, chlorpromazine and imipramine inhibited 5HT-stimulated IP-l accumulation, with Ki values of 124nM and 2560nM, respectively. Spiperone(l <micro> M) inhibitedcompletely, and clozapine(l <micro> M) and amitriptyline(l <micro> M) reduced partially(80-50%), 5HT-induced IP-l accumulation; sulpiride(l <micro> M) failed to block the 5HT response. The potencies of these compounds to inhibit 5HT-stimulated IP-l accumulation in human platelets correlates positively with the affinities to 5HT-2 receptors as defined by radioligand binding in rat cerebral cortical membranes. This extends the usefulness of the platelets as a model for 5HT-2 receptors since ligand binding studies can be complemented by measurements of a defined biochemical response.
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