Modulation of G Protein-Coupled Receptors by an Estrogen Receptor that Activates Protein Kinase A
- Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, Oregon 97201
Abstract
17β-Estradiol (E2) rapidly (<20 min) attenuates the ability of μ-opioids to hyperpolarize guinea pig hypothalamic (β-endorphin) neurons. In the current study, we used intracellular recordings from guinea pig hypothalamic slices to characterize the receptor and intracellular effector system mediating the rapid effects of E2. E2 acted stereospecifically with physiologically relevant concentration dependence (EC50 = 8 nm) to cause a 4-fold reduction in the potency of a μ-opioid agonist to activate an inwardly rectifying K+conductance. Using Schild analysis to estimate the affinity of the μ-opioid receptor for an antagonist (naloxone), we found that estrogen did not compete for the μ-opioid receptor or alter the affinity of the μ receptor. Both the nonsteroidal estrogen diethylstilbestrol and the “pure” antiestrogen ICI 164,384 blocked the actions of E2, the latter with a subnanomolar affinity. The protein synthesis inhibitor cycloheximide did not block the estrogenic uncoupling of the μ-opioid receptor from its K+ channel, implying a nongenomic mechanism of action by E2. The actions of E2 were mimicked by the protein kinase A (PKA) activators forskolin and cAMP, Sp-isomer triethylammonium salt. Furthermore, the selective PKA antagonists cAMP, Rp-isomer triethylammonium salt and KT5720, which have different chemical structures and modes of action, both blocked the effects of E2. Thus, estrogen binds to a specific receptor that activates PKA to rapidly uncouple the μ-opioid receptor from its K+ channel. Because we have previously shown that γ-aminobutyric acidB receptors are also uncoupled by estrogen, this mechanism of action has the potential to alter synaptic transmission via G protein-coupled receptors throughout the brain.
Footnotes
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Send reprint requests to: Martin J. Kelly, Ph.D., Department of Physiology & Pharmacology, Oregon Health Sciences University, Portland OR 97201. E-mail: kellym{at}ohsu.edu
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↵1 A. H. Lagrange, O. K. Rønnekleiv, and M. J. Kelly, unpublished observations.
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↵2 A. H. Lagrange, O. K. Rønnekleiv, and M. J. Kelly, unpublished observations.
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↵3 A. H. Lagrange and H. Enslen, unpublished observations.
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This work was supported by United States Public Health Service Grants DA05158 and DA00192 (Research Scientist Development Award) (M.J.K.) and MH10327 (NRSA) (A.H.L.).
- Abbreviations:
- E2
- 17β-estradiol
- DES
- diethylstilbestrol
- ER
- estrogen receptor
- BSA-E2
- bovine serum albumin/estrogen
- PKA
- cAMP-dependent protein kinase
- HPG
- hypothalamic-pituitary-gonadal axis
- GnRH
- gonadotropin-releasing hormone
- DAMGO
- [d-Ala2-N-MePhe4-Gly5-ol]enkephalin
- aCSF
- artificial cerebrospinal fluid salt solution
- Rp-cAMP
- cAMP, Rp-isomer, triethylammonium salt
- Sp-cAMP
- cAMP, Sp-isomer triethylammonium salt
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- AC
- adenylate cyclase
- RIA
- radioimmunoassay
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- Received November 26, 1996.
- Accepted December 17, 1996.
- The American Society for Pharmacology and Experimental Therapeutics
