The pharmacological properties of GABA receptor-coupled chloride channels using 36Cl-influx in cultured spinal cord neurons.
gamma-Aminobutyric acid (GABA) synaptic pharmacology was studied in cultured mouse spinal cord using various biochemical techniques. The intact cultures were used to study GABA uptake, benzodiazepine (BZ) binding and GABA-stimulated 36Cl-influx, all under similar physiological conditions. The cultures appear to contain a population of GABAergic neurons, since there was evidence of neuronal active transport of [3H]GABA by these cells. There also was a significant population of neuronal BZ receptors based on the finding of clonazepam-displaceable [3H]flunitrazepam (FLU) binding. In addition, the presence of GABA receptors coupled to the BZ receptors was shown by the enhancement of FLU binding by GABA (10-100 microM). GABAA and glycine-coupled Cl- channels were also demonstrated using 36Cl-influx. GABA-induced 36Cl-influx was specific for GABAA agonists, since GABAB receptor agonist, baclofen and other excitatory neurotransmitters did not alter the 36Cl-influx. Both GABA (Km = 9.1 microM) and muscimol (Km = 2.0 microM) produced concentration-dependent increases in 36Cl-influx in the cultures. The GABA-stimulated Cl-influx was blocked by the GABAA receptor antagonist (+)bicuculline (IC50 = 4.5 microM) and by the Cl- channel antagonist picrotoxinin (IC50 = 25 microM). These results indicate that spinal cord cultures are a useful model for comparing the binding characteristics of the GABA receptor complex to the activation of the coupled Cl- channels using the 36Cl-influx assay.
Lehoullier
P F
PF
Department of Pharmacology, University of Texas Health Science Center, San Antonio 78284-7764.
Ticku
M K
MK
D000818:Animals; D002478:Cells, Cultured; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism* / Q000493:pharmacokinetics*; D005445:Flunitrazepam / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000493:pharmacokinetics* / Q000494:pharmacology
D018118:Chloride Channels; D002712:Chlorides; D008565:Membrane Proteins; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam