Ionotropic GABA Receptor from Lobster Olfactory Projection Neurons.
A. B. Zhainazarov, M. Wachowiak, A. Boetcher, S.Elenes and B. W. Ache.
Whitney Laboratory and Depts. of 2Zoology and 3Neuroscience, Univ. of
Florida, St. Augustine, FL 32086.
APStracts 4:0049N, 1997.
ABSTRACT
This study reports an ionotropic GABA (ë-aminobutyric acid) receptor in
projection neurons acutely dissociated from the olfactory lobe of the brain of
the spiny lobster and analyzed by whole-cell and cell-free patch-clamp
recording. GABA evokes a macroscopic current in the cells that is linear from
-100 to +100 mV, reverses at the imposed chloride equilibrium potential, has a
permeability sequence of Cl- > acetate > bicarbonate > phosphate > propionate
and SCN- > Br- > I- > Cl- > F-, and is reversibly blocked by the Cl channel
blocker picrotoxin but not TBPS (tert-butylbicyclophosphorothionate). The
current is bicuculline-insensitive and activated by muscimol, isoguvacine,
CACA (cis-4-aminocrotonic acid) and TACA (trans-aminocrotonic acid), as well
as by the GABAC-receptor antagonists THIP (4,5,6,7-tetrahydroisoxazolo [5,4,-
c]pyridin-3-ol), 3-APS (3-amino-1-propanesulfonic acid) and I-4AA (imidazole-
4-acetic acid), but not the GABAB-receptor agonists baclofen and 3-APA (3-
aminopropylphosphonic acid). Agonist potency for the receptor is TACA >
muscimol > GABA > I-4AA > isoguvacine > 3-APS > CACA > THIP. Unitary chloride
currents in cell-free, outside-out patches from the cells share enough of
these pharmacological properties to indicate that the channel underlies the
macroscopic current. The receptor mediates an inhibitory current in the cells
in vivo. The receptor is similar, if not identical, to one from neurons
cultured from the thoracic ganglia of the clawed lobster (Jackel et al.,
1994a). The more extensive pharmacological characterization of the receptor
reported here indicates that this lobster CNS receptor is pharmacologically
distinct from previously characterized ionotropic GABA receptors.
Received 11 November 1996; accepted in final form 28 January 1997.
APS Manuscript Number J891-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 5 February 1997