title: Ca2+ as messenger of 5HT2-receptor stimulation in human blood platelets.
abstract: In blood platelets of man, both 5-hydroxytryptamine (5HT) and 80 nM of the Ca2+-ionophore A23187 led to rapid shape change reactions which were inhibited by prostaglandin E1 (PGE1), forskolin, 2-methyl-6-methoxy-8-nitroquinoline ( quin2 ) and chlortetracycline. The IC50-values of the inhibitors were similar in the 5HT- and the A23187-experiments. Higher amounts of A23187 abolished the inhibitory actions of PGE1 and forskolin. Furthermore, 5HT and A23187 enhanced adrenaline-induced platelet aggregation their effects showing similar time dependence. Ketanserin, an antagonist of 5HT2 -receptors, and 8-(N,N-diethyl-amino)octyl-3,4,5-trimethoxybenzoate (TMB-8), an intracellular Ca2+-antagonist, counteracted the effects of 5HT much more than those of A23187, whereas acetylsalicylate and indomethacin did not influence the actions of either 5HT or A23187. In addition, 5HT caused a concentration-dependent rise of intracellular free Ca2+ in platelets which was counteracted by ketanserin. PGE1 and forskolin reduced the resting Ca2+-levels. 5HT did not affect either the basal or the PGE1-stimulated activity of adenylate cyclase, whereas the Ca2+-ionophore A23187 slightly raised the basal activity of the enzyme. In conclusion, the functional effects of 5HT2 -receptor stimulation in human blood platelets (shape change reaction and enhancement of adrenaline aggregation) seem to be mediated by a rise of intracellular free Ca2+.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000527:Alprostadil; D001792:Blood Platelets / Q000201:enzymology / Q000502:physiology*; D001826:Body Fluids / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects; D011458:Prostaglandins E / Q000494:pharmacology; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*
chemical_list: D011458:Prostaglandins E; D011985:Receptors, Serotonin; D012701:Serotonin; D000001:Calcimycin; D000262:Adenylyl Cyclases; D000527:Alprostadil; D002118:Calcium; D004837:Epinephrine