MODULATION OF G-PROTEIN-COUPLED RECEPTORS BY AN ESTROGEN-RECEPTOR THAT ACTIVATES PROTEIN-KINASE-A

17 beta-Estradiol (E-2) rapidly (<20 min) attenuates the ability of mu -opioids to hyperpolarize guinea pig hypothalamic (beta-endorphin) neu rons. In the current study, we used intracellular recordings from guin ea pig hypothalamic slices to characterize the receptor and intracellu lar effector system mediating the rapid effects of E-2. E-2 acted ster eospecifically with physiologically relevant concentration dependence (EC50 = 8 nM) to cause a 4-fold reduction in the potency of a mu-opioi d agonist to activate an inwardly rectifying K+ conductance. Using Sch ild analysis to estimate the affinity of the mu-opioid receptor for an antagonist (naloxone), we found that estrogen did not compete for the mu-opioid receptor or alter the affinity of the mu receptor. Both the nonsteroidal estrogen diethylstilbestrol and the ''pure'' antiestroge n ICI 164,384 blocked the actions of E-2, the latter with a subnanomol ar affinity. The protein synthesis inhibitor cycloheximide did not blo ck the estrogenic uncoupling of the mu-opioid receptor from its K+ cha nnel, implying a nongenomic mechanism of action by E-2. The actions of E-2 were mimicked by the protein kinase A (PKA) activators forskolin and cAMP, Spisomer triethylammonium salt. Furthermore, the selective P KA antagonists cAMP, Rp-isomer triethylammonium salt and KT5720, which have different chemical structures and modes of action, both blocked the effects of E-2. Thus, estrogen binds to a specific receptor that a ctivates PKA to rapidly uncouple the mu-opioid receptor from its K+ ch annel. Because we have previously shown that gamma-aminobutyric acid(B ) receptors are also uncoupled by estrogen, this mechanism of action h as the potential to alter synaptic transmission via G protein-coupled receptors throughout the brain.