| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1989: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1988: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
The platelets from patients with hypercholesterolemia are known to be hyperreactive to aggregating stimuli, as compared with normal platelets. In this study to investigate the mechanism of the enhanced reactivity, the effect of cholesterol-enrichment in platelet membranes on membrane functions associated with stimulus-response system for platelet activation, using cholesterol-loaded human and rabbit platelets prepared by in vitro incubation with cholesterol-rich liposomes.
1. The cholesterol-enriched platelets were hyperaggregable to collagen, arachidonic acid, thrombin or U46619.
2. Arachidonic acid liberation from membrane phospholipids in response of [^3H]arachidonic acid-labeled platelets to collagen, thrombin or A23187, and diacylglycerol formation in response to thrombin were markedly increased.
3. The rise in intracellular Ca^<2+> Concentration in fura-2-loaded platelets stimulated with thrombin, arachidonic acid or U46619 was enhanced. The ^<45>Ca^<2+> incorporation into platelets
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was also increased by the stimulation with thrombin or U46619.
4. GTPgamma S-induced stimulation, that is independent of receptor-operated mechanism, of the membranes isolated from the [^3H]arachidonic acid-labelled, cholesterol-enriched platelets, caused significantly increased arachidonic acid liberation but not diacylglycerol formation, as compared with the membranes from normal platelets.
5. The number of binding sites for thromboxane A_2 which was examined using [^3H]U46619, was significantly higher in cholesterol-loaded platelets than in normal platelets, but not the change in the affinity.
6. The rearrangement of platelet cytoskeletal proteins, actin and myosin, was markedly enhanced by the stimulation with phorbol ester and A23187 in the platelets with a high cholesterol content.
These results suggest that a certain physical change in cholesterol-enriched membranes increases the receptor responsiveness, phospholipase A_2 activity and Ca^<2+> influx, which are the essential membrane functions for platelet activation, therefore resulting in the enhanced aggregability to the agonists. Less
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