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Biomedical subjects

M Hirouchi

Publications and source records attributed to M Hirouchi.

28 records · Page 2Linked to original sources
PubMed1990

Functional coupling of the gamma-aminobutyric acidB receptor with calcium ion channel and GTP-binding protein and its alteration following solubilization of the gamma-aminobutyric acidB receptor.

The coupling mechanism of the gamma-aminobutyric acid (GABA)B receptor, one of the subtypes of GABA receptors, with calcium ion channel and GTP-binding protein was examined using a crude synaptic membrane (P2) fraction from the bovine cerebral cortex and a fraction solubilized with sodium deoxycholate. In the P2 fraction, [3H]GABA binding to the GABAB receptor was increased significantly by the addition of calcium ion, and this enhancement was accentuated further by calcium ion channel blockers such as nicardipine and diltiazem. In contrast, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a calmodulin antagonist, did not affect on the calcium ion-induced enhancement of GABAB receptor binding. These results suggest that the GABAB receptor may be functionally coupled with the calcium ion channel, which exhibits an inhibitory modulation against the receptor. On the other hand, GABAB receptor binding, which was noncompetitively inhibited by guanine nucleotides such as GTP, guanosine 5'-(3-O-thio)triphosphate (GTP gamma S), guanosine 5'-(beta, gamma-imido)triphosphate [Gpp(NH)p], and GDP, was competitively inhibited by (-)-baclofen. Although the affinity of (-)-baclofen for the GABAB receptor was decreased in the presence of GTP, pretreatment of the P2 fraction with islet-activating protein (IAP) eliminated the effect of GTP. In addition, GABA and (-)-baclofen induced an increase of GTPase activity in the P2 fraction, and this increase was also eliminated by treatment with IAP. These results suggest that the GABAB receptor may also be functionally coupled with IAP-sensitive GTP-binding protein. Treatment of the P2 fraction with sodium deoxycholate resulted in the highest solubilization of GABAB receptor among various detergents examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

[Structure and function of gamma-aminobutyric acid (GABA) receptor: current state and prospectives].

The gamma-aminobutyric acid (GABA) receptor has been classified into two receptor subtypes (GABAA and GABAB receptors) based on their pharmacological properties. The GABAA receptor in the central nervous system (CNS) has been found to be coupled structurally as well as functionally with the benzodiazepine receptor and Cl- channel. Purified GABAA receptor from bovine brain consisted of both alpha and beta subunits. The complementary DNAs encoding the GABAA receptor alpha and beta subunits have been cloned; and from their elucidated nucleotide sequences, the amino acid sequences of the subunits were deduced. The structure of both subunits, having four putative membrane domains, has been found to be similar to other ligand-gated receptors such as the nicotinic acetylcholine receptor alpha subunit and glycine receptor 48K subunit. Therefore, it has been suggested that these ligand-gated receptors comprise a superfamily. In addition, the presence of similarities in the nucleotide and deduced amino acid sequences of human brain GABAA receptor with those of bovine brain has been noted. On the other hand, the GABAB receptor, which is insensitive to bicuculline but sensitive to baclofen, has been found to be pharmacologically distinct from the GABAA receptor. The GABAB receptor in the brain has been found to be coupled with GTP-binding protein and generates the inhibitory transmission coupled with various intracellular effector systems such as adenylate cyclase and phosphoinositides turnover. The exact structure and function of the GABAB receptor in the CNS, however, remain to be clarified in future studies.

Amino Acid Sequence↗
PubMed1988

Inactivation of peroxidases of rat bone marrow by repeated administration of propylthiouracil is accompanied by a change in the heme structure.

Myeloperoxidase and eosinophil peroxidase were isolated from the bone marrow cells of rats treated with or without propylthiouracil (PTU) which caused bone marrow depression. PTU treatment decreased the activity of myeloperoxidase but not of eosinophil peroxidase using guaiacol as the electron donor. However, when KI,N-N'-dimethyl-p-phenylenediamine and pyrogallol were used as the electron donor, the activity of only eosinophil peroxidase was inhibited by PTU treatment. EPR spectra indicated that the structure of myeloperoxidase surrounding the heme iron changed from a rhombic form into an axial one by the repeated administration of PTU. Therefore, the inactivation of peroxidases by PTU treatment was accompanied by an alteration of their structures surrounding the heme.

Animals↗
PubMed1988

[Effect of buflomedil on cerebral acetylcholine, neuroactive amino acids contents and energy metabolism: analysis using spontaneously hypertensive rat (SHR)].

Effects of continuous oral administration of Buflomedil on acetylcholine (ACh) and neuroactive amino acids contents and energy metabolism in the brain were investigated using Wistar Kyoto rat (WKY) and spontaneously hypertensive rat (SHR). In both WKY and SHR, continuous oral administration of Buflomedil (30 mg/kg x 7 days) had no effect on ACh content in all cerebral areas examined. On the other hand, continuous oral administration of Buflomedil to SHR induced a significant increase in the contents of glutamic acid and taurine in the striatum and hypothalamus, while it resulted in a significant decrease in the contents of glycine and taurine in the midbrain and hippocampus. Glucose and ATP contents in the striatum of SHR showed a significant increase following the continuous oral administration of Buflomedil. These results suggest that Buflomedil may be a drug capable of improving various neuropsychiatric symptoms associated with cerebrovascular insufficiency by modifying the content of neuroactive amino acids and accelerating energy metabolism in the brain.

Acetylcholine↗
PubMed1987

GABA-stimulated 36Cl- influx into reconstituted vesicles with purified GABAA/benzodiazepine receptor complex.

Solubilized and Purified gamma-aminobutyric acid (GABA)A receptors from membrane vesicles of the bovine cerebral cortex were reconstituted into phospholipid vesicles and 36Cl- influx into the vesicles was examined. GABA induced a significant stimulation of the 36Cl- influx into reconstituted vesicles with 1.5% CHAPS/0.15% asolectin solubilized receptor and flunitrazepam further enhanced the GABA-stimulated influx. The purification of GABAA/benzodiazepine receptor complex and Cl- channel solubilized by 1.5% CHAPS/0.15% asolectin from membrane vesicles was achieved by 1012-S affinity column chromatography. The reconstituted vesicles with the purified receptor complex and Cl- channel also exhibited GABA-stimulated 36Cl- influx. This GABA-stimulated influx of 36Cl- was also enhanced by flunitrazepam, while suppressed by bicuculline, a GABAA receptor antagonist. These results strongly suggest that GABAA receptor is directly coupled with Cl- channel, whereas benzodiazepine receptor may be functionally coupled with GABAA receptor and modulates the GABA-stimulated Cl- influx through GABAA receptor. The present results also indicate that the purified GABAA receptor complex is coupled with Cl- channel and possesses functional characteristics as GABAA receptor.

Animals↗
PubMed1987

Purification and some properties of peroxidases of rat bone marrow.

Myeloperoxidase and eosinophil peroxidase were separated and purified from rat bone marrow cells using cetyltrimethylammonium bromide as the solubilizer and then with column chromatographies on CM-Sephadex C-50 and Con A-Sepharose. Both purified enzymes were observed to be apparently homogeneous by SDS-polyacrylamide gel electrophoresis. Myeloperoxidase consisted of two subunits of Mr 57,000 and 15,000, and eosinophil peroxidase two of 53,000 and 14,000. On structural analysis of the enzymes, their visual and ESR spectra revealed that the structure surrounding the heme in myeloperoxidase was different from that in eosinophil peroxidase. Moreover, substrate specificity and sensitivity to inhibitors such as azide and cyanide differed between the two enzymes. Rat bone marrow possesses two distinct peroxidases, myeloperoxidase and eosinophil peroxidase, which have different subunits and different heme microenvironments. Therefore, the difference in enzymatic function between the two peroxidases may be due to their structures.

Animals↗
PubMed1987

Effects of alcohol and acetaldehyde on metabolism and function of neurotransmitter systems in cerebral cortical neurons in primary culture.

Effects of alcohol (ethanol) and acetaldehyde (AcAl) on the metabolism and function of gamma-amino-butyric acid (GABA)ergic and cholinergic systems were investigated using mouse cerebral cortical neurons in primary culture. Exposure to alcohol in vitro had no significant effects on the content of neuroactive amino acids as well as the activities of glutamic acid decarboxylase (GAD), GABA-transaminase (GABA-T), choline acetyltransferase (CAT) and acetylcholinesterase (AChE). In contrast, AcAl showed remarkable reductions of neuroactive amino acids content, and of CAT and AChE activities, but induced no alteration in the activities of GAD and GABA-T. [3H]Flunitrazepam [( 3H]FLN) binding and the stimulatory effect of GABA on [3H]FLN binding were found to be inhibited by in vitro exposure to both alcohol and AcAl, both of which, however, induced no changes in [3H]muscimol binding. These results suggest that the direct actions of AcAl on cholinergic systems in primary cultured neurons may be more potent than those of alcohol. The results described above also suggest that alcohol-induced neurochemical alterations in vivo may be, at least in part, caused by AcAl converted from alcohol in vivo.

Acetaldehyde↗
PubMed1984

Relationship between leukopenia and bone marrow myeloperoxidase in the rat treated with propylthiouracil.

The relationship between the toxic effect of propylthiouracil (PTU) and myeloperoxidase activity of rat bone marrow was examined. The administration of PTU for 1 or 2 weeks caused a decrease in leukocyte count with the concomitant inhibition of the activity of myeloperoxidase in the bone marrow. The decreases in both leukocyte counts and myeloperoxidase activity were restored to control levels at 2 weeks after the discontinuation of the administration. PTU treatment did not affect the affinity of H2O2 for the enzyme; however, an increase in the Km value for guaiacol was seen. PTU, incubated with bone marrow peroxidase in vitro increased the Km value of the enzyme for guaiacol, but had no effect on the Km value for H2O2. The results suggest that the mechanism of inhibition of myeloperoxidase activity by PTU given in vivo or incubated with the enzyme in vitro may be the same. The activity of bone marrow glutathione peroxidase was not influenced by PTU treatment.

Animals↗