5-hydroxytryptamine2C receptor activation inhibits 5-hydroxytryptamine1B-like receptor function via arachidonic acid metabolism.
We previously reported that in Chinese hamster ovary (CHO) cells, 5-hydroxytryptamine (5-HT)1B-like (CHO/5-HT1B) receptor-mediated inhibition of forskolin-stimulated cAMP accumulation is inhibited by activation of transfected human 5-HT2C receptors but not 5-HT2A receptors. In the current study, we investigated the mechanism involved in the regulation of receptor-mediated inhibition of adenylyl cyclase as a means to further elucidate differences between the signal transduction cascades of the 5-HT2A and 5-HT2C receptor subtypes. Activation of 5-HT2C receptors with 5-HT or (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane increased release of arachidonic acid via a phospholipase A2 (PLA2)-dependent mechanism. Incubation with (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (1 microM) abolished 5-carboxamidotryptamine (5 nM)-mediated inhibition of forskolin-stimulated cAMP accumulation, which was blocked by the PLA2 inhibitor mepacrine (100 microM) and the cyclooxygenase inhibitor indomethacin (2 microM). Furthermore, purinergic receptor-mediated PLA2 activation as well as direct activation of PLA2 with melittin reduced CHO/5-HT1B responsiveness. These data indicate that activation of the PLA2/arachidonic acid signaling cascade mediates 5-HT2C receptor regulation of the CHO/5-HT1B receptor pathway. Consistent with our previous report and in contrast to activation of 5-HT2C or purinergic receptors, activation of 5-HT2A receptors had no effect on CHO/5-HT1B receptor function, although 5-HT2A receptor-mediated activation of PLA2 was measured. Interestingly, purinergic receptor-mediated inhibition of CHO/5-HT1B receptor function was blocked when 5-HT2A receptors were activated simultaneously. These data suggest that the lack of 5-HT2A mediated regulation of CHO/5-HT1B receptors may be due to activation of a third pathway (in addition to PLC and PLA2 pathways), which results in the inhibition of the production or the actions of a cyclooxygenase-dependent arachidonic acid metabolite.
Berg
K A
KA
Department of Pharmacology, University of Texas Health Science Center at San Antonio 78284-7764, USA. berg@uthscsa.edu
Maayani
S
S
Clarke
W P
WP
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D016466:CHO Cells / Q000502:physiology / Q000648:ultrastructure; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism*; D016861:Cyclooxygenase Inhibitors / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism / Q000502:physiology*; D054467:Phospholipases A2; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D044405:Receptor, Serotonin, 5-HT2C; D011983:Receptors, Purinergic / Q000502:physiology; D011985:Receptors, Serotonin / Q000145:classification / Q000235:genetics / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D014162:Transfection
D016861:Cyclooxygenase Inhibitors; D044405:Receptor, Serotonin, 5-HT2C; D011983:Receptors, Purinergic; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D016718:Arachidonic Acid; D000242:Cyclic AMP; D011451:Prostaglandin-Endoperoxide Synthases; D010741:Phospholipases A; D054467:Phospholipases A2; D007213:Indomethacin