Anomalous rectifying properties of 'diazepam-insensitive' GABA(A) receptors.
Studies using recombinant systems indicate that 'diazepam-insensitive' GABA(A) receptors in the central nervous system contain alpha4 and alpha6 subunits while 'diazepam-sensitive' GABA(A) receptors contain alpha1, alpha2, alpha3 and alpha5 subunits. Both native and recombinant diazepam-sensitive GABA(A) receptors typically exhibit large, outwardly rectifying currents. For example, in patch clamp studies, Human Embryonic Kidney (HEK) 293 cells transfected with cDNAs encoding alpha1beta2gamma2 subunits exhibit a rectification ratio (I +60 mV/I -60 mV) of 1.95 +/- 0.21. However, anomalous rectification was observed in recombinant diazepam-insensitive GABA(A) receptors composed of either alpha4beta2gamma2 (rectification ratio, 0.74 +/- 0.09) or alpha6beta2gamma2 (rectification ratio, 0.67 +/- 0.11) subunits. Based on sequence differences between diazepam-sensitive and -insensitive GABA(A) receptor alpha subunits in the vicinity of the putative channel lining, a point mutation was introduced at His273 on the alpha4 subunit. The rectification ratio in cells expressing a mutated alpha4(Asn273)beta2gamma2 receptor increased to 1.92 +/- 0.17. Moreover, mutation of the homologous residue in the alpha1 subunit to histidine reduced the rectification ratio of alpha1(His274)beta2gamma2 to 1.02 +/- 0.12. The affinities of benzodiazepine site ligands at diazepam-sensitive and -insensitive GABA(A) receptors were unaffected by these mutations. Thus, the electrophysiological properties of diazepam-sensitive and -insensitive GABA(A) receptors may be as divergent as their pharmacological characteristics.
Granja
R
R
Laboratory of Neuroscience, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA.
Strakhova
M
M
Knauer
C S
CS
Skolnick
P
P
D000595:Amino Acid Sequence; D002460:Cell Line; D003975:Diazepam / Q000494:pharmacology*; D004594:Electrophysiology; D018757:GABA Modulators / Q000494:pharmacology*; D006801:Humans; D007536:Isomerism; D008024:Ligands; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D017354:Point Mutation / Q000502:physiology; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000235:genetics*
D018757:GABA Modulators; D008024:Ligands; D011963:Receptors, GABA-A; D003975:Diazepam