Abstract
NIH3T3 cells stably expressing the rat 5-hydroxytryptamine2A (5-HT2A) 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 A2(PLA2) signal transduction pathways. Initial experiments were designed to verify that 5-HT2A receptor-mediated PLA2 activation in NIH3T3 cells is independent from, and not a subsequent result of, 5-HT2A receptor-mediated PLC activation. In addition, we also explored the extent of receptor reserve for the endogenous ligand, 5-HT, for both PLC and PLA2 activation. Finally, we employed structurally diverse ligands from the tryptamine, phenethylamine, and ergoline families of 5-HT2A receptor agonists to test the hypothesis of agonist-directed trafficking of 5-HT2A receptor-mediated PLC and PLA2 activation. To measure agonist-induced pathway activation, we determined the potency and intrinsic activity of each compound to activate either the PLA2 pathway or the PLC pathway. The results showed that a larger receptor reserve exists for 5-HT-induced PLA2 activation than for 5-HT-induced PLC activation. Furthermore, the data support the hypothesis of agonist-directed trafficking in NIH3T3–5HT2A cells because structurally distinct ligands were able to induce preferential activation of the PLC or PLA2 signaling pathway. From these data we conclude that structurally distinct ligands can differentially regulate 5-HT2A receptor signal transduction.
Footnotes
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This work was supported by National Institutes of Health Grant DA02189. Portions of this work have been presented at the annual meeting of the Society for Neuroscience (2000, 2001) and the biannual meeting of the Serotonin Club (2000).
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DOI: 10.1124/jpet.102.042184
- Abbreviations:
- GPCR
- G protein-coupled receptor
- 5-HT
- 5-hydroxtryptamine, serotonin
- PLA2
- phospholipase A2
- PLC
- phospholipase C
- AA
- arachidonic acid
- IP
- a mixture of inositol monophosphate, inositol bisphosphate, and inositol triphosphate
- RHC-80267
- 1,6-bis-(cyclohexyloximinocarbonylamino)hexane
- d-LSD
- d-lysergic acid diethylamide
- DAG
- diacylglycerol
- PBZ
- phenoxybenzamine
- DOB
- 1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane
- Received July 25, 2002.
- Accepted September 25, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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