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Biomedical subjects

J H Chin

Publications and source records attributed to J H Chin.

At least 37 records · Page 2Linked to original sources
PubMed1986

A new class of adenosine receptors in brain. Characterization by 2-chloro[3H]adenosine binding.

Micromolar concentrations of adenosine and its analogs have profound depressant effects on neuronal firing and synaptic transmission in many brain areas. Using the adenosine agonist 2-chloro[3H]adenosine (Cl[3H]Ado), we have identified a distinct class of micromolar-affinity adenosine binding sites in rat forebrain membranes. Specific Cl[3H]Ado binding was reversible and saturable with an apparent KD of 9.1 microM and a Bmax of 61 pmoles/mg protein. The present studies were conducted using washed brain membrane fractions not treated with adenosine deaminase. Specific Cl[3H]Ado binding under these conditions was insensitive to (-)-N6-(R-phenylisopropyl)adenosine ((-)PIA) and treatment with 3 mM N-ethylmaleimide, unlike high-affinity A1 adenosine receptor binding. Treatment of membranes with adenosine deaminase revealed an additional population of binding sites sensitive to (-)PIA. Inhibition of Cl[3H]Ado binding by adenosine analogs exhibited an order of potency ClAdo greater than 5'-N-ethylcarboxamide adenosine (NECA) greater than (-)PIA which differs from that of both A1 and A2 adenosine receptors. The potent A1 and A2 receptor antagonist 8-phenyltheophylline had no significant effect on binding up to 10 microM. Specific binding, however, was inhibited by the adenosine antagonists 8(p-sulfophenyl)theophylline, isobutylmethylxanthine, theophylline, and caffeine. Micromolar Cl[3H]Ado binding was highly selective for adenosine agonists and antagonists. These results suggest that the micromolar-affinity Cl[3H]Ado binding sites may represent a novel central purinergic receptor, distinct from the A1 and A2 adenosine receptors involved in the regulation of adenylate cyclase.

2-Chloroadenosine↗
PubMed1986

Treatment of irresectible hepatocellular carcinoma with intrahepatic arterial lipoidal mixed with adriamycin and mitomycin C.

Four patients with advanced hepatocellular carcinoma, but with stage I functional disease, were treated with intrahepatic arterial lipoidal mixed with small doses of Adriamycin (20 mg) and Mitomycin C (10 mg). Regression was seen in 3 out of the 4 patients. In 2 patients, there was substantial regression of tumour clinically, radiologically and biochemically. The treatment was tolerable without marrow depression or deterioration of liver function. Mild fever (37 degrees C) was seen in 2 and epigastric pain in 1. This form of treatment opens up scope for further improvement in the management of irresectable hepatocellular carcinoma.

Adult↗
PubMed1985

Cobalt ion enhancement of 2-chloro[3H]adenosine binding to a novel class of adenosine receptors in brain: antagonism by calcium.

We have recently reported the identification of a novel class of micromolar-affinity adenosine binding sites in rat brain membranes using the adenosine agonist 2-chloro[3H]adenosine (C1[3H]Ado). These binding sites are distinguishable from the A1 and A2 adenosine receptors by a number of pharmacological criteria, and we have designated this new class of binding sites as the A3 adenosine binding sites. In the present study, the effects of a wide range of divalent and trivalent cations on micromolar C1[3H]Ado binding to brain membranes were examined. Co2+, Ni2+ and La3+ markedly stimulated specific C1[3H]Ado binding by 45-150% above control when tested at concentrations of 1-10 mM. Ca2+ had no significant effect on binding except at high concentrations where it depressed binding slightly. Ca2+, however, completely prevented the stimulation of C1[3H]Ado binding by Co2+. These findings further distinguish the A3 class of adenosine binding sites from the previously characterized adenosine receptors and suggest that the A3 binding sites are associated with calcium systems in brain.

2-Chloroadenosine↗
PubMed1985

Novel adenosine receptors in rat hippocampus. Identification and characterization.

2-Chloro[3H]adenosine, a stable analog of adenosine, was used to investigate the presence of adenosine receptors in rat hippocampal membranes that may mediate the depressant effects of adenosine on synaptic transmission in this tissue. Equilibrium binding studies reveal the presence of a previously undescribed class of receptors with a KD of 4.7 microM and a Bmax of 130 pmol/mg of protein. Binding is sensitive to alkylxanthines and to a number of adenosine-related compounds. The pharmacological properties of this binding site are distinct from those of the A1 and A2 adenosine receptors associated with adenylate cyclase. The results suggest that this adenosine binding site is a novel central purinergic receptor through which adenosine may regulate hippocampal excitability.

2-Chloroadenosine↗
PubMed1985

Decreased membrane fluidity and beta-adrenergic responsiveness in atherosclerotic quail.

The effects of increased cholesterol on erythrocyte membrane fluidity and beta-adrenergic function were studied in a quail model of atherosclerosis. Birds fed a cholesterol-supplemented diet developed severe atherosclerosis and hypercholesterolemia after 6 wk. This cholesterol-enriched diet led to a markedly elevated serum cholesterol and a 26% increase in the cholesterol-to-phospholipid ratio in erythrocyte membranes. Electron paramagnetic resonance spectra measured with 5- and 12-doxyl-stearic acid spin-label probes were used to estimate the order of quail erythrocyte membranes. Membrane preparations from cholesterol-fed birds were more highly ordered near the membrane leaflet surface, as well as deeper in the membrane interior, compared with controls. beta-Adrenergic receptor stimulation of adenosine 3',5'-cyclic monophosphate accumulation was blunted in erythrocytes from the hypercholesterolemic quail. There was no change in beta-receptor density or affinity in the cholesterol-enriched membranes. These studies demonstrate that cholesterol incorporation into erythrocyte membranes in vivo is associated with decreased membrane fluidity and decreased beta-adrenergic responsiveness. The atherosclerotic quail may serve as a useful model to further probe the sequelae of hypercholesterolemia on the function of integral membrane proteins.

Animals↗
PubMed1984

Cholesterol blocks the disordering effects of ethanol in biomembranes.

To assess the relation between the physical order of a membrane and its sensitivity to ethanol, we enriched biomembranes with cholesterol, both in vivo and in vitro. Japanese quail of the SEA line (selectively bred for susceptibility to experimental atherosclerosis) were treated for 9 to 16 weeks with a diet that contained 2% cholesterol. This regimen increased the cholesterol content of serum and erythrocytes. The cholesterol content of brain synaptosomal plasma membranes (SPM) was unaffected by the high cholesterol diet. In other experiments, isolated mouse synaptosomal plasma membranes were incubated with cholesterol/phospholipid (C/P) vesicles; different amounts of cholesterol were transferred according to the sterol content of the donor vesicles. Membrane order was determined in both types of membranes by a sensitive electron paramagnetic resonance (EPR) technique. The order parameter with 5- and 12-doxylstearic acid increased along with the cholesterol content. As expected, ethanol disordered membranes (decreased the order parameter) in a concentration-related manner. The slope of the concentration response curve was less steep in high cholesterol than low cholesterol membranes, indicating that cholesterol enrichment partially blocks the membrane action of ethanol in both types of membranes.

Animals↗
PubMed1982

Ethanol disordering of spin-labeled mouse brain membranes: correlation with genetically determined ethanol sensitivity of mice.

Disordering of brain and erythrocyte membranes by ethanol in vitro was measured by ESR using 5-doxylstearic acid as spin label. Synaptosomal plasma membranes and erythrocyte membranes were isolated from two lines of mice developed, by selective breeding, for differential sensitivity to hypnotic effects of ethanol. Membranes taken from alcohol-sensitive "long-sleep" mice were more strongly disordered by ethanol in vitro than were membranes from alcohol-resistant "short-sleep" mice. Furthermore, within a population of genetically heterogeneous mice, the most ethanol-sensitive animals had the most ethanol-sensitive synaptosomal plasma membranes. In vivo sensitivity of the individual mice was evaluated by measuring brain ethanol levels at a precise behavioral end point, recovery from ataxia. The data extend our previous observations of correlations between in vitro and in vivo effects of ethanol and suggest that membrane disordering may be a primary mechanism of acute effects of ethanol.

Animals↗
PubMed1981

Endogenous lectin from chick embryo skeletal muscle is not involved in myotube formation in vitro.

Antisera against a beta-D-galactoside-specific lectin purified to homogeneity from embryonic chick thigh muscle and from adult chicken livers were raised in rabbits. The sera contained antibodies which strongly inhibited the hemagglutinin activity of the lectin. Immune and preimmune [125I]IgG and [125I]Fab preparations were tested for ability to bind to monolayers of cultured chick myoblasts and showed no significant differences in binding. Thus, we were unable to detect the lectin on the cell surface. When added to myoblast cultures, the purified lectin had no influence on the process of myoblast fusion. Furthermore, neither anti-lectin IgG nor Fab fragments interfered with myotube formation when present at high concentration in fusing cultures. On the basis of these results, we conclude that intercellular interactions between the lectin and complementary cell surface receptors do not play a role in myoblast adhesion and fusion in vitro.

Animals↗
PubMed1981

Interaction of ethanol with biological membranes.

Ethanol is among the drugs with anesthetic potency determined by lipid solubility, in accord with the Meyer-Overton hypothesis. Thus, it is likely that ethanol acts in a hydrophobic environment. Using electron paramagnetic resonance with 5-doxylstearic acid as spin label, we find that ethanol disorders mouse cell membranes, making the lipid matrix more fluid. We surmise that consequent disruption of the function of integral membrane proteins may be the cause of ethanol's central actions. When mice are treated for 8 days with ethanol, their membranes become tolerant to the disordering effect of ethanol. This tolerance is accompanied by an increased proportion of cholesterol in the membranes.

Animals↗
PubMed1980

Effects of aliphatic alcohols and aldehydes on fluidity of spin-labeled synaptosomal plasma membranes.

Synaptosomal plasma membranes from Swiss-Webster mice were spin-labeled with 5-doxylstearic acid. By electron paramagnetic resonance techniques an order parameter was measured. A decrease in the order parameter reflected an increase in membrane fluidity. In confirmation of our previous work, ethanol decreased membrane order. Pentanol also showed a concentration-related decrease in the order parameter in the range of 23 to 87 mM. At equimolar concentrations, pentanol was about 9 times more effective than ethanol. Acetaldehyde had no effect on membrane fluidity at concentrations that might be found in vivo during ethanol oxidation (23 or 227 microM) but a very high concentration, 2.3 mM, produced a small decrease in the order parameter comparable to the effect of an intoxicating concentration of ethanol. Valeraldehyde also had a slight fluidizing effect and appeared very roughly three times more potent than acetaldehyde. This study shows that the fluidizing effects of ethanol are not shared by its aldehyde metabolite at relevant concentrations. The fluidizing effects of aldehydes are slight but they increase with concentration and with chain length.

Alcohols↗
PubMed1979

Fluidity and lipid composition of mouse biomembranes during adaptation to ethanol.

Showing that ethanol added in vitro increased the fluidity of mouse erythrocyte and synaptosomal membranes and that the same membranes isolated from mice after chronic treatment with ethanol had increased cholesterol and were resistant to ethanol in vitro, the study suggests that the animals had adapted to the chronic presence of the drug by changing their membrane lipid composition to offset the fluidizing effects of ethanol.

Animals↗
PubMed1978

Increased cholesterol content of erythrocyte and brain membranes in ethanol-tolerant mice.

Mice were treated with ethanol for eight or nine days, using a liquid diet regimen known to produce physical dependence. In previous experiments, synaptosomal plasma membranes and erythrocyte ghosts from such ethanol-treated animals were found to be resistant to the fluidizing effects of ethanol in vitro, as measured by electron paramagnetic resonance. In the present experiments, corresponding membranes were analysed for phospholipid and cholesterol. The ratio of cholesterol to phospholipid was found to be significantly increased in both types of membrane after chronic ethanol treatment. The changed ratio was produced by an increase in cholesterol. There was little or no change in phospholipid content of the membranes. Increased cholesterol may explain the previously observed alteration of physical properties of the membranes.

Animals↗
PubMed1977

Drug tolerance in biomembranes: a spin label study of the effects of ethanol.

Ethanol in vitro increased the fluidity of spin-labeled membranes from normal mice. Membranes from mice that had been subjected to long-term ethanol treatment were relatively resistant to this fluidizing effect. The data suggest that the membranes themselves had adapted to the drug, a novel form of drug tolerance.

Adaptation, Physiological↗
PubMed1977

Electron paramagnetic resonance studies of ethanol on membrane fluidity.

An optimum level of fluidity in the membrane appears to be important for some physiological functions. The present studies examined the effects of ethanol in erythrocyte and brain membrane preparations from Swiss Webster mice using electron paramagnetic resonance (EPR) techniques with a fatty acid spin label. The spectral parameter measured was the order parmeter, S, an index of membrane fluidity. Synaptosomal membranes were more fluid than myelin but less fluid than mitochondrial membranes. In low concentrations of 1 and 2 mg/ml of ethanol membrane fluidity was increased in mitochondrial, synaptosomal, and erythrocyte membranes. Dose-related increases in membrane fluidity were also observed at higher concentrations of 4, 8 and 16 mg/ml of ethanol for all of the membranes except myelin. These data indicate that non-lethal concentrations of ethanol may increase membrane fluidity in vivo.

Animals↗