The 5-hydroxytryptamine receptor of blood platelets.

Blood platelets show specific, high affinity binding of 3H-5-hydroxytryptamine, 3H-ketanserin and 3H-D-lysergic acid diethylamide. 5-HT-antagonists are considerably more potent than agonists regarding both the displacement of specifically bound 3H-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 for 3H-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.