Different effects of pentobarbital on two. gamma. -aminobutyrate receptors from rat brain: channel opening, desensitization, and an additional conformational change

Journal Article · Tue Jun 14 04:00:00 EDT 1988 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00412a053· OSTI ID:6998226

Cash, D J; Subbarao, K

The effect of pentobarbital on the responses of the ..gamma..-aminobutyric acid (GABA) receptor from rat brain was studied in quantitative measurements of GABA-mediated chloride-exchange rates (reflecting channel-opening equilibrium) and receptor desensitization rates by using /sup 36/Cl/sup -/ tracer ion with negative membrane vesicles. Pentobarbital effected the two phases of /sup 36/Cl/sup -/ influx in different ways, supporting previous evidence that these are mediated by two different receptors. Both the chloride-exchange rate and the desensitization rate of the faster desensitizing receptor were increased by pentobarbital at concentrations above 20 ..mu..M by an allosteric effect shifting the response curve to lower GABA concentrations. A similar enhancement of the responses of the slower desensitizing receptor occurred up to 200 ..mu..M pentobarbital. Two pentobarbital effector sites were involved in the allosteric mechanism. Above 500 ..mu..M pentobarbital, both the initial chloride-exchange rate and the desensitization rate of the slower desensitizing receptor were decreased. This inhibition, which was immediate, occurred with saturating as well as low GABA concentrations and therefore was not attributed to decreased GABA binding but to inhibitory sites for pentobarbital, different from the allosteric activating sites and the GABA binding sites. The chloride ion exchange activity was seen to recover with time, at concentrations above 1000 ..mu..M pentobarbital, in a process with a very steep dependence on pentobarbital concentration. This reactivation was attributed to the conversion of an initial form of the receptor to a final form that was less inhibited by pentobarbital. Comparisons of the effects of pentobarbital on desensitization and on high-affinity ligand binding measurements suggest that increased GABA binding at equilibrium reflects an increased conversion to the desensitized state.

• Research Organization: Univ. of Missouri-Columbia, St. Louis (USA)
• OSTI ID: 6998226
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:12; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
AMINOBUTYRIC ACID
ANESTHETICS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
AZINES
BARBITURATES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOLOGICAL EFFECTS
BODY
BRAIN
CARBOXYLIC ACIDS
CENTRAL NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM DEPRESSANTS
CHLORINE 36
CHLORINE ISOTOPES
CONFORMATIONAL CHANGES
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
HETEROCYCLIC COMPOUNDS
HYPNOTICS AND SEDATIVES
ISOTOPES
LIGHT NUCLEI
MAMMALS
MEMBRANE PROTEINS
MEMBRANE TRANSPORT
NEMBUTAL
NERVOUS SYSTEM
NEUROREGULATORS
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANS
PROTEINS
PYRIMIDINES
RADIOISOTOPES
RATS
RECEPTORS
RODENTS
VERTEBRATES
YEARS LIVING RADIOISOTOPES