The effects of the neurosteroids: pregnenolone, progesterone and dehydroepiandrosterone on muscarinic receptor-induced responses in Xenopus oocytes expressing M1 and M3 receptors.
The neurosteroids pregnenolone, progesterone, and dehydroepiandrosterone (DHEA) occur naturally in the nervous system. They act on neural tissues, participate in neuronal signaling, and are reported to alter neuronal excitability via nongenomic mechanisms. Muscarinic receptors have important roles in neuronal functions in the brain and autonomic nervous system. In this study, we investigated the effects of pregnenolone, progesterone, and DHEA on M(1) and M(3) muscarinic receptors using the Xenopus oocyte expression system. Pregnenolone and progesterone inhibited the acetylcholine (ACh)-mediated responses of M(1) and M(3) receptors expressed in Xenopus oocytes, whereas DHEA did not. The half-maximal inhibitory concentrations (IC(50)) for pregnenolone inhibition of M(1) receptor- and M(3) receptor-mediated currents were 11.4 and 6.0 microM respectively; the IC(50) values for progesterone inhibition of M(1) receptor- and M(3) receptor-mediated currents were 2.5 and 3.0 microM respectively. The selective protein kinase C (PKC) inhibitor GF109203X had little effect on the pregnenolone or progesterone inhibition of the ACh-induced currents in Xenopus oocytes expressing M(1) or M(3) receptors. The inhibitory effects of pregnenolone and progesterone were overcome at higher concentrations of ACh. Pregnenolone and progesterone inhibited the [(3)H]quinuclidinyl benzilate (QNB) binding to M(1) and M(3) receptor expressed in Xenopus oocytes, and Scatchard plot analysis of [(3)H]QNB binding revealed that pregnenolone and progesterone altered the K(d) value and the B(max), indicating noncompetitive inhibition. In conclusion, pregnenolone and progesterone inhibited M(1) and M(3) receptor functions noncompetitively by the mechanism independent of PKC and by interfering with ACh binding to the receptors.
Horishita
Takafumi
T
Department of Anesthesiology, School of Medicine, University of Occupational and Environmental Health, Yahatanishiku, Kitakyushu 807-8555, Japan.
Minami
Kouichiro
K
Uezono
Yasuhito
Y
Shiraishi
Munehiro
M
Ogata
Junichi
J
Okamoto
Takashi
T
Terada
Tadanori
T
Sata
Takeyoshi
T
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D003001:Cloning, Molecular; D003687:Dehydroepiandrosterone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D007211:Indoles / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D008301:Maleimides / Q000494:pharmacology; D018727:Muscarinic Antagonists; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011284:Pregnenolone / Q000494:pharmacology*; D011374:Progesterone / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011813:Quinuclidinyl Benzilate; D018075:RNA, Complementary / Q000096:biosynthesis; D011869:Radioligand Assay; D051381:Rats; D043643:Receptor, Muscarinic M1 / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D043587:Receptor, Muscarinic M3 / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
D018118:Chloride Channels; D007211:Indoles; D008301:Maleimides; D018727:Muscarinic Antagonists; D018075:RNA, Complementary; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D003687:Dehydroepiandrosterone; D011374:Progesterone; D011813:Quinuclidinyl Benzilate; D011284:Pregnenolone; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D000109:Acetylcholine; D002118:Calcium