Serotonin 5-hydroxytryptamine 2A receptor-coupled phospholipase C and phospholipase A2 signaling pathways have different receptor reserves.
NIH3T3 cells stably expressing the rat 5-hydroxytryptamine 2A (5-HT 2A) receptor (5500 fmol/mg) were used to explore further the capacity of structurally distinct ligands to elicit differential signaling through the phospholipase C (PLC) or phospholipase A 2 (PLA 2) signal transduction pathways. Initial experiments were designed to verify that 5-HT 2A receptor-mediated PLA 2 activation in NIH3T3 cells is independent from, and not a subsequent result of, 5-HT 2A receptor-mediated PLC activation. In addition, we also explored the extent of receptor reserve for the endogenous ligand, 5-HT, for both PLC and PLA 2 activation. Finally, we employed structurally diverse ligands from the tryptamine, phenethylamine, and ergoline families of 5-HT 2A receptor agonists to test the hypothesis of agonist-directed trafficking of 5-HT 2A receptor-mediated PLC and PLA 2 activation. To measure agonist-induced pathway activation, we determined the potency and intrinsic activity of each compound to activate either the PLA 2 pathway or the PLC pathway. The results showed that a larger receptor reserve exists for 5-HT-induced PLA 2 activation than for 5-HT-induced PLC activation. Furthermore, the data support the hypothesis of agonist-directed trafficking in NIH3T3-5HT 2A cells because structurally distinct ligands were able to induce preferential activation of the PLC or PLA 2 signaling pathway. From these data we conclude that structurally distinct ligands can differentially regulate 5-HT 2A receptor signal transduction.
Kurrasch-Orbaugh
Deborah M
DM
Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
Watts
Val J
VJ
Barker
Eric L
EL
Nichols
David E
DE
D016475:3T3 Cells; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004873:Ergolines / Q000494:pharmacology; D006868:Hydrolysis; D008024:Ligands; D051379:Mice; D010627:Phenethylamines / Q000494:pharmacology; D010643:Phenoxybenzamine / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D011869:Radioligand Assay; D051381:Rats; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014363:Tryptamines / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D000317:Adrenergic alpha-Antagonists; D004791:Enzyme Inhibitors; D004873:Ergolines; D008024:Ligands; D010627:Phenethylamines; D010716:Phosphatidylinositols; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D014363:Tryptamines; D010643:Phenoxybenzamine; D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases