The 5-hydroxytryptamine receptor of blood platelets

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Abstract
Blood platelets show specific, high affinity binding of3H-5-hydroxytryptamine,3H-ketanserin and3H-D-lysergic acid diethylamide. 5-HT-antagonists are considerably more potent than agonists regarding both the displacement of specifically bound3H-ketanserin and the shape change reaction mediated by the 5-HT-receptor. The latter depends on a rise of free intracellular Ca2. The binding site for3H-ketanserin and the site at which the 5-HT-induced shape change is triggered show the characteristics of a 5-HT2-receptor whose intracellular mediator seems to be Ca2+. The 5-HT2-receptor of platelets may be used as a partial model for that in neurons; however, it remains to be elucidated whether Ca2+ is a mediator of the latter. Studies of receptors in blood platelets are of interest for several reasons. In platelets, the investigation of a whole chain of events is possible, starting with receptor-ligand interaction and leading via intracellular messengers to the expression of a morphological alteration,e.g. in case of the 5-hydroxytryptamine (5-HT) receptor the shape change reaction. Furthermore, the 5-HT-receptors of platelets have certain similarities with those of the central nervous system (CNS), which is one of the reasons why platelets can be used as a limited model for neurons. Finally, platelets are easily accessible, intact cells enabling receptor studies in man as a complement to animal experiments.