Channel opening of. gamma. -aminobutyric acid receptor from rat brain: molecular mechanisms of the receptor responses

Journal Article · Tue Dec 01 04:00:00 EST 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00398a005· OSTI ID:5303772

Cash, D J; Subbarao, K

The function of ..gamma..-aminobutyric acid (GABA) receptors, which mediate transmembrane chloride flux, can be studied by use of /sup 36/Cl/sup -/ isotope tracer with membrane from mammalian brain by quench-flow technique, with reaction times that allow resolution of the receptor desensitization rates from the ion flux rates. The rates of chloride exchange into the vesicles in the absence and presence of GABA were characterized with membrane from rat cerebral cortex. Unspecific /sup 36/Cl/sup -/ influx was completed in three phases of ca. 3% (t/sub 1/2/ = 0.6 s), 56% (t/sub 1/2 = 82 s), and 41% (t/sub 1/2 = 23 min). GABA-mediated, specific chloride exchange occurred with 6.5% of the total vesicular internal volume. The GABA-dependent /sup 36/Cl/sup -/ influx proceeded in two phases, each progressively slowed by desensitization. The measurements supported the presence of two distinguishable active GABA receptors on the same membrane mediating chloride exchange into the vesicles. The half-response concentrations were similar for both receptors. The two receptors were present in the activity ratio of ca. 4/1, similar to the ratio of low affinity to high-affinity GABA sites found in ligand binding experiments. The desensitization rates have a different dependence on GABA concentration than the channel-opening equilibria. For both receptors, the measurements over a 2000-fold GABA concentration range required a minimal mechanism involving the occupation of both of the two GABA binding sites for significant channel opening; then the receptors were ca. 80% open. Similarly for both receptors, desensitization was mediated by a different pair of binding sites, although desensitization with only one ligand molecule bound could occur at a 20-fold slower rate.

• Research Organization: Univ. of Missouri, St. Louis
• OSTI ID: 5303772
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:24; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METAL COMPOUNDS
AMINO ACIDS
AMINOBUTYRIC ACID
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BODY
BRAIN
CALCIUM CHLORIDES
CALCIUM COMPOUNDS
CALCIUM HALIDES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL MEMBRANES
CENTRAL NERVOUS SYSTEM
CHLORIDES
CHLORINE 36
CHLORINE COMPOUNDS
CHLORINE ISOTOPES
DOSE-RESPONSE RELATIONSHIPS
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
HALIDES
HALOGEN COMPOUNDS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNESIUM CHLORIDES
MAGNESIUM COMPOUNDS
MAMMALS
MEMBRANE PROTEINS
MEMBRANE TRANSPORT
MEMBRANES
NERVOUS SYSTEM
NEUROREGULATORS
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANS
PROTEINS
RADIOISOTOPES
RATS
REACTION KINETICS
RECEPTORS
RODENTS
SENSITIVITY
TRACER TECHNIQUES
VERTEBRATES
YEARS LIVING RADIOISOTOPES