title: Channel gating in the absence of agonist by a homo-oligomeric molluscan GABA receptor expressed in Xenopus oocytes from a cloned cDNA.
abstract: We have previously described the isolation of a complementary DNA (cDNA) from the freshwater mollusc Lymnaea stagnalis encoding a polypeptide that exhibits approximately 50% identity to the beta-subunits of vertebrate gamma-aminobutyric acid (GABA) type A (GABAA) receptor. When expressed in Xenopus laevis oocytes from in vitro-transcribed RNA, the snail subunit forms functional homo-oligomeric receptors possessing chloride-selective ion channels. In recordings from voltage-clamped oocytes held at -60 mV, GABA induced an inward current, whereas application of the chloride-channel blocker picrotoxin (in the absence of agonist) elicited an apparent outward current. Single channel recordings obtained from cell-attached patches have revealed a single population of approximately 20 pS channels, with an open probability greater than 90% (at a pipette potential of -100 mV) in the absence of GABA. The relationship between single channel current and pipette potential was linear over the studied range (-100 mV to +60 mV), but the open probability was less for hyperpolarizations than for depolarizations. The spontaneous channel openings were blocked by micromolar concentrations of picrotoxin. Functional hetero-oligomeric receptors were formed when the molluscan subunit was co-expressed in oocytes with the bovine GABAA receptor alpha 1-subunit, but the channels gated by these receptors did not open spontaneously.
authors.affiliation: Department of Life Science, University of Nottingham, UK.
authors.forename: N S
authors.initials: NS
authors.lastname: Bhandal
authors.forename: R L
authors.initials: RL
authors.lastname: Ramsey
authors.forename: R J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: M G
authors.initials: MG
authors.lastname: Darlison
authors.forename: P N
authors.initials: PN
authors.lastname: Usherwood
mesh_terms: D000818:Animals; D002417:Cattle; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008195:Lymnaea; D008974:Mollusca / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D018079:Receptors, GABA / Q000737:chemistry / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014982:Xenopus laevis / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D018076:DNA, Complementary; D007473:Ion Channels; D018079:Receptors, GABA; D010566:Virulence Factors, Bordetella; D005680:gamma-Aminobutyric Acid