title: Analysis of G-protein-activated inward rectifying K(+) (GIRK) channel currents upon GABAB receptor activation in rat supraoptic neurons.
abstract: While magnocellular neurons in the supraoptic nucleus (SON) possess rich Gi/o-mediated mechanisms, molecular and cellular properties of G-protein-activated inwardly rectifying K(+) (GIRK) channels have been controversial. Here, properties of GIRK channels are examined by RT-PCR and whole-cell patch-clamp techniques in rat SON neurons. Patch clamp experiments showed that the selective GABAB agonist, baclofen, enhanced currents in a high K(+) condition. The baclofen-enhanced currents exhibited evident inward rectification and were blocked by the selective GABAB antagonist, CGP55845A, the IRK channel blocker, Ba(2+), and the selective GIRK channel blocker, tertiapin, indicating that baclofen activates GIRK channels via GABAB receptors. The GIRK currents were abolished by N-ethylmaleimide pretreatment, and prolonged by GTPγS inclusion in the patch pipette, suggesting that Gi/o proteins are involved. RT-PCR analysis revealed mRNAs for all four GIRK 1-4 channels and for both GABABR1 and GABABR2 receptors in rat SON. However, the concentration-dependency of the baclofen-induced activation of GIRK currents had an EC50 of 110 µM, which is about 100 times higher than that of baclofen-induced inhibition of voltage-dependent Ca(2+) channels. Moreover, baclofen caused no significant changes in the membrane potential and the firing rate. These results suggest that although GIRK channels can be activated by GABAB receptors via the Gi/o pathway, this occurs at high agonist concentrations, and thus may not be a physiological mechanism regulating the function of SON neurons. This property that the membrane potential receives little influence from GIRK currents seems to be uncommon for CNS neurons possessing rich Gi/o-coupled receptors, and could be a special feature of rat SON neurons.
authors.affiliation: Critical Care Medicine, University Hospital, University of Occupational and Environmental Health, Kitakyushu 807-8556, Japan.
authors.forename: Nobuya
authors.initials: N
authors.lastname: Harayama
authors.affiliation: Laboratory of Veterinary Physiology, Joint Department of Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan.
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Kayano
authors.affiliation: Laboratory of Veterinary Physiology, Joint Department of Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan.
authors.forename: Taiki
authors.initials: T
authors.lastname: Moriya
authors.affiliation: Laboratory of Veterinary Physiology, Joint Department of Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Kitamura
authors.affiliation: Laboratory of Veterinary Physiology, Joint Department of Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan. Electronic address: shibuya@muses.tottori-u.ac.jp.
authors.forename: Izumi
authors.initials: I
authors.lastname: Shibuya
authors.affiliation: Center for Functional Connectomics, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea.
authors.forename: Keiko
authors.initials: K
authors.lastname: Tanaka-Yamamoto
authors.affiliation: Division of cancer pathophysiology, National Cancer Center Research Institute, Tokyo 104-0045, Japan.
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Uezono
authors.affiliation: Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ueta
authors.affiliation: Department of Anesthesiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan.
authors.forename: Takeyoshi
authors.initials: T
authors.lastname: Sata
mesh_terms: D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D017208:Rats, Wistar; D018080:Receptors, GABA-B / Q000378:metabolism*; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000378:metabolism*
chemical_list: D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D018080:Receptors, GABA-B; D001418:Baclofen
keywords: GABA(B) receptors; GIRK channels; Gi/o; Patch clamp; RT-PCR; Supraoptic nucleus