Abstract
The serotonin2C (5-HT2C) receptor couples to multiple effector mechanisms, including phospholipase A2-mediated arachidonic acid (AA) release and phospholipase C-mediated production of inositol phosphates (IP). Agonist relative efficacy differs depending upon which response (AA release or IP accumulation) is measured. In this study, we investigated the characteristics and agonist dependence of rapid desensitization of 5-HT2C receptor-mediated AA release and IP accumulation measured simultaneously from the same cell population. Pretreatment with 5-HT reduced the ability of a maximal concentration of 5-HT to elicit AA release and IP accumulation by about 60%; however, the AA response desensitized more rapidly (t1/2 = 1.3 min) than the IP response (t1/2 = 6.9 min). In addition, desensitization of the IP response was more sensitive (occurred at lower receptor occupancy levels) than the AA response. Moreover, in response to submaximal 5-HT concentrations, after an initial transient desensitization, the AA response was enhanced by up to ∼250%. After maximal desensitization, both responses recovered, but recovery of the AA response was complete and faster than that for IP. Desensitization of both responses was also agonist-dependent, and the capacity of agonists to elicit desensitization was not related to their efficacy to activate signaling. These data suggest that desensitization of the 5-HT2C receptor system is both agonist- and effector pathway-dependent and underscore the need to study multiple cellular responses to multiple agonists to understand receptor-mediated signaling systems.
Footnotes
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This work was supported by U.S. Public Health Service Grants DA 09094 (to K.A.B.) and GM 58652 and the Texas Advanced Research Program (3569-0044; to W.P.C. and K.A.B.).
- Abbreviations:
- 5-HT
- serotonin
- 7-TMS
- seven transmembrane spanning
- PLC
- phospholipase C
- PI
- phosphatidylinositol
- PLA2
- phospholipase A2
- AA
- arachidonic acid
- IP
- inositol phosphates
- CHO
- Chinese hamster ovary
- LSD
- lysergic acid diethylamide
- mCPP
- 1-(3-chlorophenyl)piperazine
- TFMPP
- 3-trifluotomethylphenyl-piperazine
- Received February 5, 2002.
- Accepted March 25, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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