Channel gating in the absence of agonist by a homo-oligomeric molluscan GABA receptor expressed in Xenopus oocytes from a cloned cDNA

• Published in: Invertebrate neuroscience Vol. 1; no. 3; p. 267
• Main Authors: Bhandal, N S, Ramsey, R L, Harvey, R J, Darlison, M G, Usherwood, P N
• Format: Journal Article
• Language: English
• Published: Germany 01.12.1995
• Subjects: Animals; Cattle; Cloning, Molecular; DNA, Complementary - genetics; Female; gamma-Aminobutyric Acid - pharmacology; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Ion Channels - drug effects; Ion Channels - physiology; Lymnaea; Mollusca - metabolism; Oocytes - metabolism; Patch-Clamp Techniques; Receptors, GABA - chemistry; Receptors, GABA - metabolism; Virulence Factors, Bordetella - pharmacology; Xenopus laevis - metabolism
• ISSN: 1354-2516
• DOI: 10.1007/BF02211028

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.