Ultraviolet irradiation selectively disrupts the gamma-aminobutyric acid/benzodiazepine receptor-linked chloride ionophore.
The ability of UV light to affect radioligand binding and 36Cl-uptake at the gamma-aminobutyric acidA (GABAA) receptor-chloride channel complex was examined. Exposure to 302 nm UV light produced a rapid (t1/2 = 4 min) reduction in [35S]t-butylbicyclo-phosphorothionate binding (assayed in the presence of 200 mM chloride) to sites associated with the GABAA receptor-coupled chloride ionophore. Saturation analysis revealed that this effect could be attributed entirely to a decrease in the maximum number of binding sites. Exposure to UV irradiation at lower (254 nm) and higher (366 nm) wavelengths also inhibited [35S]t-butylbicy-clophosphorothionate binding, but the respective rates of inactivation were 8- and 27-fold slower, compared with 302 nm. Other anion-dependent interactions at the GABAA receptor complex were disrupted in a similar manner. In the absence of permeant anion, [3H]flunitrazepam binding to benzodiazepine receptors was unaffected by 302 nm UV irradiation, whereas chloride-enhanced [3H]flunitrazepam binding was inhibited markedly. In the presence of 250-500 mM chloride, [3H]methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate binding to benzodiazepine receptors was also inhibited after UV exposure. Basal 36Cl- uptake into synaptoneurosomes was nearly doubled after 15 min of exposure to 302 nm light, whereas pentobarbital- and muscimol-stimulated 36Cl- uptake were reduced significantly. UV irradiation at 302 nm appears to disrupt selectively the anion-dependent functional interactions at the GABAA receptor complex. The apparent wavelength specificity suggests that the gating structure (channel) may contain tryptophan and/or tyrosine residues vital to the regulation of anion movement through the ionophore portion of this supramolecular receptor-ion channel complex.
Evoniuk
G
G
Laboratory of Neuroscience, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Moody
E J
EJ
Skolnick
P
P
D000818:Animals; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002243:Carbolines / Q000378:metabolism; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D005445:Flunitrazepam / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008565:Membrane Proteins; D051381:Rats; D011919:Rats, Inbred Strains; D011963:Receptors, GABA-A / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002243:Carbolines; D018118:Chloride Channels; D002712:Chlorides; D008565:Membrane Proteins; D011963:Receptors, GABA-A; C034818:methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; C037476:tert-butylbicyclophosphorothionate