Incremental conductance levels of GABAA receptors in dopaminergic neurones of the rat substantia nigra pars compacta.
1. Molecular and biophysical properties of GABAA receptors of dopaminergic (DA) neurones of the pars compacta of the rat substantia nigra were studied in slices and after acute dissociation. 2. Single-cell reverse transcriptase-multiplex polymerase chain reaction confirmed that DA neurones contained mRNAs encoding for the alpha3 subunit of the GABAA receptor, but further showed the presence of alpha4 subunit mRNAs. alpha2, beta1 and gamma1 subunit mRNAs were never detected. Overall, DA neurones present a pattern of expression of GABAA receptor subunit mRNAs containing mainly alpha3/4beta2/3gamma3. 3. Outside-out patches were excised from DA neurones and GABAA single-channel patch-clamp currents were recorded under low doses (1-5 microM) of GABA or isoguvacine, a selective GABAA agonist. Recordings presented several conductance levels which appeared to be integer multiples of an elementary conductance of 4-5 pS. This property was shared by GABAA receptors of cerebellar Purkinje neurones recorded in slices (however, with an elementary conductance of 3 pS). Only the 5-6 lowest levels were analysed. 4. A progressive change in the distribution of occupancy of these levels was observed when increasing the isoguvacine concentration (up to 10 microM) as well as when adding zolpidem (20-200 nM), a drug acting at the benzodiazepine binding site: both treatments enlarged the occupancy of the highest conductance levels, while decreasing that of the smallest ones. Conversely, Zn2+ (10 microM), a negative allosteric modulator of GABAA receptor channels, decreased the occupancy of the highest levels in favour of the lowest ones. 5. These properties of alpha3/4beta2/3gamma3-containing GABAA receptors would support the hypothesis of either single GABAA receptor channels with multiple open states or that of a synchronous recruitment of GABAA receptor channels that could involve their clustering in the membranes of DA neurones.
Guyon
A
A
Neurobiologie Cellulaire, Institut des Neurosciences, CNRS-Universite Pierre et Marie Curie, 9 quai Saint-Bernard, F-75005 Paris, France. alice.guyon@snv.jussieu.fr
Laurent
S
S
Paupardin-Tritsch
D
D
Rossier
J
J
Eugène
D
D
D000818:Animals; D004298:Dopamine / Q000502:physiology*; D004594:Electrophysiology; D018755:GABA Agonists / Q000494:pharmacology; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D007539:Isonicotinic Acids / Q000494:pharmacology; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011689:Purkinje Cells / Q000187:drug effects / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D000077334:Zolpidem
D018755:GABA Agonists; D006993:Hypnotics and Sedatives; D007539:Isonicotinic Acids; D011725:Pyridines; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D000077334:Zolpidem; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine; C015300:isoguvacine