Glycoprotein as a constituent of purified gamma-aminobutyric acid/benzodiazepine receptor complex: structures and physiological roles of its carbohydrate chain

The effect of treatments with various enzymes and chemically modifying agents on [3H]muscimol binding to a purified gamma-aminobutyric acid (GABA)/benzodiazepine receptor complex from the bovine cerebral cortex was examined. Treatments with pronase, trypsin, guanidine hydrochloride, and urea significantly decreased the binding of [3H]muscimol, but dithiothreitol, N-ethylmaleimide, reduced glutathione, oxidized glutathione, cysteine, and cystine had no significant effect. These results indicate that the GABA receptor indeed consists of protein, but -SH and -S-S- groups in the protein are not involved in the exhibition of the binding activity. On the other hand, column chromatography using concanavalin A-Sepharose eluted protein having [3H]muscimol binding activity and staining of glycoprotein using an electrophoresed slab gel indicated the existence of two bands originating from the subunits of the GABA/benzodiazepine receptor complex. Furthermore, treatments with various glycosidases such as glycopeptidase A, beta-galactosidase, and alpha-mannosidase significantly increased the binding of [3H]muscimol. These results strongly suggest that GABA/benzodiazepine receptor complex is a glycoprotein and that its carbohydrate chain may be a hybrid type. Treatment with beta-galactosidase resulted in the disappearance of the low-affinity site for [3H]muscimol binding and in an increase of Bmax of the high-affinity site, without changing the KD value. These results suggest that the carbohydrate chain in the receptor complex may have a role in exhibiting the low-affinity binding site for GABA. The observation that the enhancement of [3H]muscimol binding by treatments with beta-galactosidase and glycopeptidase A were much higher than that with alpha-mannosidase may also indicate a special importance of the beta-galactosyl residue in the inhibition of GABA receptor binding activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol, acetaldehyde and salsolinol-induced alterations in functions of cerebral GABA/benzodiazepine receptor complex

Effects of alcohol (ethanol) and acetaldehyde on the metabolism and function of primary cultured GABAergic neurons and that of salsolinol, a condensation product of acetaldehyde with dopamine, on cerebral GABA/benzodiazepine (BZP) receptor complex were investigated. In vitro addition of acetaldehyde induced a significant reduction not only on the content of GABA but also on the basal and GABA-activated [3H]flunitrazepam ([3H]FLN) bindings in primary cultured neurons. In contrast, alcohol exhibited only suppressive effects on [3H]FLN binding as well as on the enhancement of [3H]FLN binding by GABA. On the other hand, salsolinol showed a significant stimulatory effect on [3H]FLN binding to cerebral particulate fractions obtained from alcohol-untreated mice in the presence of NaCl. Although a similar activation of cerebral [3H]FLN binding by salsolinol was found in alcohol-treated mice, this activation was significantly weaker in alcohol-withdrawn mice than those found in alcohol-untreated as well as alcohol-inhaled mice. These results strongly suggest that acetaldehyde may have more important pathophysiological roles than those of alcohol in the exhibition of neurotoxicity during alcohol intake. The present results also suggest that salsolinol may have a modulatory role on cerebral benzodiazepine receptor and the decreased capacity of such a modulating mechanism may be involved in the exhibition of alcohol withdrawal syndrome, possibly by decreasing the function of endogenous ligands for benzodiazepine receptor in the brain.

Purification of gamma-aminobutyric acid (GABA) receptor from rat brain by affinity column chromatography using a new benzodiazepine, 1012-S, as an immobilized ligand

The purification of gamma-aminobutyric acid (GABA) and benzodiazepine receptors from the rat brain was employed by the affinity column using a new benzodiazepine, 1012-S, as immobilized ligand. The 1012-S has a aliphatic primary amino group and exhibited an extremely high potency for displacing [3H]flunitrazepam binding to solubilized benzodiazepine receptor preparation (IC50 = 6.0 X 10(-11) M). This benzodiazepine affinity gel retained almost all of the solubilized GABA receptors from synaptic membranes applied to the column, and 25.6% of the receptor was eluted bio-specifically following the application of 1 mM 1012-S. The highest purification fold thus obtained was 4576 (specific activity: 0.99 nmol/mg protein). Furthermore, the successive application of 1-2 M NaSCN also resulted the elution of a highly enriched GABA receptor (specific activity: 0.41 nmol/mg protein; purification fold: 1889). SDS-polyacrylamide gel electrophoretic profiles of the bio-specifically eluted fraction with 1012-S showed the existence of two major bands having the molecular weights of approximately 48,500 and 54,500, in which the former band was selectively photoaffinity-labeled with [3H]flunitrazepam. On the other hand, it was found that the non-specifically eluted fraction with NaSCN contained 4 additional minor bands having molecular weights of 41,000 to 51,000. These results indicate that GABA receptor of the rat brain is coupled, at least in part, with benzodiazepine receptor and is readily purified by the use of highly specific benzodiazepine affinity gel, 1012-S-acetamide adipic hydrazide Sepharose 4B. The present results also suggest that the purified GABA/benzodiazepine receptor complex may contain two different kinds of subunits having the molecular weights of 48,000 and 54,500, in which the former subunit may possess benzodiazepine binding sites.

Stress-induced enhancement of suppression of [3H]GABA release from striatal slices by presynaptic autoreceptor

The effect of cold and immobilization stress on presynaptic GABAergic autoreceptors was examined using the release of [3H]GABA (gamma-aminobutyric acid) from slices of rat striatum. It was found that in vitro addition of delta-aminolevulinic acid, as well as GABA agonists such as muscimol and imidazoleacetic acid, exhibited a significant suppression of the striatal release of [3H]GABA evoked by the addition of high potassium, whereas delta-aminovaleric acid had no significant effects on the evoked release. These suppressive actions were antagonized invariably by the GABA antagonists, bicuculline and picrotoxin, but not by the glycine antagonist, strychnine. Cholinergic agonists, such as pilocarpine and tetramethylammonium, also attenuated significantly the evoked release of [3H]GABA from striatal slices, while none of its antagonists, including atropine, hexamethonium and d-tubocurarine, affected the release. On the other hand, in vitro addition of dopamine receptor agents such as dopamine, apomorphine, and haloperidol, or the inhibitory amino acids, glycine, beta-alanine, and taurine failed to influence the evoked release of [3H]GABA from striatal slices. Application of a cold and immobilization stress for 3 h was found to induce a significant enhancement of the suppressive effects by muscimol and delta-aminolevulinic acid on the evoked release of [3H]GABA, without affecting that by pilocarpine and tetramethylammonium. These results suggest that the release of GABA from striatal GABA neurons may be regulated by presynaptic autoreceptors for this neuroactive amino acid, and may play a significant functional role in the exhibition of various symptoms induced by stress.

[Treatment of urinary tract infections by cefaclor, with special reference to the antibody-coated bacteria (ACB) detected by the immunoenzyme technique]

Twenty out-patients suffering from urinary tract infections (UTI) were treated with cefaclor. Cefaclor was administrated orally in daily doses of 1,500 mg for 7 days against 15 cases of simple UTI and 5 cases of complicated UTI. Of 20 cases with acute simple cystitis, acute pyelonephritis and complicated UTI, clinical responses were excellent in 10 cases, good in 6 cases and poor in 4 cases. The efficacy rate was 80%. No side effect was observed. The site of infection determined by the ACB detection method was in good agreement with that determined by clinical findings. Cefaclor appeared to be equally effective in the treatment of both ACB-positive and ACB-negative infections. The presence of absence of antibody-coated bacteria did not correlate with clinical symptoms or response to therapy.

[Absorption and excretion of cefotaxime and its levels in uterine arterial blood, female internal genital organ tissue and pelvic cavity fluid (author's transl)]

Following results were obtained from intravenous single administration of cefotaxime 2 g by measuring its levels in uterine arterial blood, elbow venous blood, ovary, oviduct, several sites in uterine tissue, and in the fluid excreted in the dead space formed by radical hysterectomy. (1) Uterine artery and elbow vein blood levels revealed marked increase immediately after administration followed by gradual reduction at slow rate. (2) Peak levels in female internal genital organ tissue were achieved 12 approximately 19 minutes after cefotaxime administration, and ranged between 5 to 8 mcg/g independently from measurement site. In cervix uteri, portio vaginalis high concentration of 4.9 approximately 5.7 mcg/g was achieved within ten minutes after drug administration. (3) In the fluid excreted in the dead space formed by radical hysterectomy cefotaxime levels were maintained around 15 mcg/ml level throughout 5 approximately 6 hours following its administration, and gradually decreased at slow rate later.

Brain level of pentobarbital is the primary determinant for the development of hypnotic of hypnotic tolerance in mice

Controlling the duration of hypnotic effect of pentobarbital by simultaneously administered bemegride, the relationship between the duration of hypnosis and the degree of developed tolerance after acute or chronic treatment was investigated in mice. Bemegride attenuated the hypnotic effect of pentobarbital, but neither the brain level of pentobarbital nor the development of tolerance was modified by bemegride, indicating that the brain level of pentobarbital is the primary determinant for the production of tolerance and full duration of hypnosis is not essential in this mechanism.

Partial versus complete control of blood pressure in the prevention of hypertensive complications

The data from the Veterans Administration Cooperative Study on Antihypertensive Agents Prevention of Morbidity Trial were reviewed from the point of view of the importance of normalizing the blood pressure in preventing cardiovascular complications. The treated group of patients was subdivided into three subgroups on the basis of the diastolic blood pressures recorded at the fourth month after randomization as follows: subgroup A, the poorly controlled patients whose diastolic blood pressures were 90 mm Hg or higher, an intermediate subgroup B with diatolic levels of 81 to 89 mm Hg, and subgroup C, the best controlled patients, all of whom exhibited diastolic blood pressures of 80 mm Hg or less. While the incidence of morbid events was slightly higher in subgroup A than in the other subgroups, the differences were not statistically significant. On the other hand, the incidence of morbid events in subgroup A was significantly lower (P less than 0.05) than in the untreated control patients (14.9% in subgroup A vs. 28.9% in the control group). While normalization of blood pressure is a desirable goal of treatment, even partial reduction appears to exert significant therapeutic benefit.