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Biomedical subjects

A Guidotti

Publications and source records attributed to A Guidotti.

At least 253 records · Page 14Linked to original sources
PubMed1979

Molecular mechanisms regulating the interactions between the benzodazepines and GABA receptors in the central nervous system.

Using radioreceptor assay techniques to measure the kinetics of GABA and diazepam receptors, a relationship between GABA and benzodiazepine receptors has been firmly established in membranes of brain and neuroblastoma NB2a clonal cell lines. Occupancy of benzodiazepine receptors uncovers a new population of GABA receptors (GABA2 receptors) endowed with high affinity for GABA. Moreover, stimulation of GABA receptors increases the affinity of 1,4-benzodiazepine receptors for 1,4-benzodiazepines. This reciprocal interaction appears to be mediated by an endogenous regulatory protein (for details on this protein see [14 and 29]) which allosterically regulates GABA2 receptors while it competitively interacts with benzodiazepines for their specific binding sites. The rank order of potency of the various 1,4-benzodiazepines to block the action of this protein inhibitor on GABA receptors is related to their capacity to displace 3H-diazepam binding. These data suggest that the interaction between the 1,4-benzodiazepine receptors and the endogenous protein modulator of GABA2 receptors might play a role in the pharmacological action of the 1,4-benzodiazepines.

Animals↗
PubMed1979

1,4-Benzodiazepines and gamma-aminobutyric acid: pharmacological and biochemical correlates.

The high affinity receptors or GABA present in brain interact with an endogenous thermostable inhibitor (GABA modulin) which allosterically modifies GABA binding sites. This is the type of GABA receptor that we term GABA2 receptor in comparison to GABA1 receptor which has low affinity for GABA and is not regulated by GABA modulin. The 1,4-benzodiazepines interact competitively with GABA modulin and thereby modify GABA2 receptor binding. In contrast the occupancy of GABA receptor increases the affinity of 1,4-benzodiazepine receptors for their specific agonist. The GABA modulin and both GABA receptors are located on the membranes of C6 and NB2a cells. The NB2a cell membranes also contain CL- ionophore, thus the complete receptor complex is present in the membranes of NB2a cell clone. It was proposed that the inability of clonazepam to displace 3H-diazepam from specific binding sites characterizes the nonneuronal 1,4-benzodiazepine receptor. This characterization was shown to relate to the properties of other membrane components rather than to the characteristics of the specific benzodiazepine receptors.

Animals↗
PubMed1978

Purification of an endogenous protein inhibitor of the high affinity binding of gamma-aminobutyric acid to synaptic membranes of rat brain.

In a medium without Na+, gamma-aminobutyric acid (GABA) binds at 0 degrees to freshly prepared crude synaptic membranes from rat cerebral cortex with an apparent dissociation constant of 218 nM. An endogenous inhibitor of the Na+-independent GABA binding was removed from these membranes by freezing and thawing and by repeated washing with Tris citrate buffer (50 mM, pH 7.1) containing 0.01% Triton X-100. As a result, the crude synaptic membranes bind GABA at 0 degrees with two dissociation constants, 20 nM and 111 nM. The endogenous inhibitor is a thermostable (95 degrees for 15 min) acidic protein of approximately 1.5 X 10(4) daltons. It was purified (about 500-fold) with a series of procedures including gel chromatography on Sephadex G-100 and ion exchange chromatography on Dowex 50W-X8 (H+). Recombination of the purified endogenous inhibitor with crude synaptic membrane preparations deprived of the endogenous inhibitor showed that the purified inhibitor blocked noncompetitively the sites for high-affinity GABA binding. A role of this endogenous regulator in the functional of GABA-ergic synapses is discussed.

Animals↗
PubMed1978

Molecular mechanisms mediating the action of diazepam on GABA receptors.

Two types of crude synaptic membranes have been prepared which differ in their kinetic properties to bind 3H-GABA in a Na+-free medium. One type (B) has one type of receptor (affinity or KD about 0.2 micrometer), the other type (A) has two populations of receptors which have a high (0.16 micrometer) and a low ((.02 micrometer) KD for GABA binding. This difference is due to the presence of a selective endogenous inhibitor of the high affinity receptor for GABA, a thermostable protein of about 15,000 molecular weight. Inhibitor action is counteracted by diazepam (7 X 10(-7) M), competitively. Clonazepam is more active but chlordiazepoxide is less active than diazepam. Two enantiomers of a benzodiazepine were studied. One of them is endowed with anxiolytic activity and nullifies the action of the endogenous inhibitor on high affinity GABA binding, the other is devoid of anxiolytic activity and is inactive against the inhibitor. The endogenous protein inhibitor also competitively blocks the high affinity binding of 3H-diazepam to Type A membranes. It is concluded that the endogenous inhibitor and diazepam act on the same receptor; and suggested that the endogenous inhibitor may be the natural ligand for the brain receptors that bind benzodiazepines with high affinity.

Animals↗