Rapid effects of estrogen to modulate G protein-coupled receptors via activation of protein kinase A and protein kinase C pathways

17 beta-Estradiol (E-2) rapidly (<20 min) attenuates the ability of mu-opioids to hyperpolarize guinea pig hypothalamic neurons. We have used intracellular recordings from female guinea pig hypothalamic slices to characterize the receptor and intracellular pathway(s) mediating E-2's rapid effects. E-2 acts stereospecifically with physiologically relevant concentration-dependcnce (EC50 = 8 nM) to cause a fourfold reduction in the potency of the mu-opioid agonist (D-Ala(2)-N-Me-Phe(4)-Gly(5)-ol)-enkephalin and the GABA(B), agonist baclofen to activate an inwardly rectifying KC conductance in hypothalamic neurons. Both the nonsteroidal estrogen diethylstilbestrol and the anti-estrogen ICI 164,384 blocked E-2 actions to uncouple mu-opioid receptors. Using a pharmacological Schild analysis, we found that ICI 164,384 competed for this E-2 receptor with a K-c of approximately 0.3 nM. The protein synthesis inhibitor cycloheximide did not block the estrogenic uncoupling of the mu-opioid receptor from its K+ channel, implying a rapid, nongenomic mechanism of E-2 action. The effects of E-2 were mimicked by the bath application of the protein kinase A (PKA) activators, forskolin and Sp-cAMP, and the protein kinase C (PKC) activator phorbol-12,13-dibutyrate. Furthermore, the selective PKA antagonists Rp-cAMP and KT5720, which have different chemical structures and modes of action, both blocked the effects of E-2. In addition, the actions of E-2 were blocked by the selective PKC inhibitor Calphostin C. Therefore, it appears that E-2 can activate both PKA and PKC to cause a heterologous desensitization of both mu-opioid and GABA(B) receptors, which has the potential to alter synaptic transmission in many regions of the CNS. (C) 1999 Elsevier Science Inc. All rights reserved.