Effect of Soman on the Nicotinic Acetylcholine Receptor / 第二军医大学学报

The highly specific ligand of the N-acetylcholine receptor (N-AChR) was used to determine the effect of scman, sarin and VX on N-AChR of the diaphragm, and extensor digitorum longus muscle of the mouse and rat The effects of the three anticholinesterase agents on N-AChR were different Sarin didn't directly act on N-AChR and cause a change in the number of N-AChR VX decreased the binding site of the receptor through directly binding N-AChR The ID50 was 0.054 mg/kg mouse. Soman increased the binding sites, e.g. 1-1.5 LD50 soman increased the N-AChR of mouse diaphragm for 25% of the control. The increase in N-AChR was up to a highest peak 0.5 h after poisoning and continued for 96 h. The receptor number was still 22% higher than that of the control on the fourth day after soman poisoning in the rat Soman mainly increased the number of extrasynaptic N-AChR, leading to the enhancement of sensitivity of cholinergic effector to ACh. This simulates the sensibilization resulting from denervation. These findings are of significance in probing the receptor mechanisms and treatment of the soman poisoning.

EFFECT OF ALLOSTERIC SNAKE NEUROTOXIN ON NEUROMUSCULAR JUNCTION / 第二军医大学学报

The present study reports direct effects of allosteric snake neurotoxin (MN-81) on the nicotinic acetylcholine receptor (N-AChR) and on the transmission of nuro-muscular junction. when one dose of MN-81 with 50 ?g/kg body weight was injected into the mice, the number of N-AChR binding sites was not changed. when one dose of MN-81 with 250 ng/kg body weight was injected, 23 per cent of total N-AChR were occupied by MN-81 molecules. But when repeated injection of MN-81 was carried out N-AChR binding sites were increased by about 34 percent. Assay of phrenic nerve-diaphragm showed that the low close of MN-81 increased contractile amplitude of isolated rat diaphragm and rabbit diaphragm in situ, while an increase in the concentration of MN-81 (10-4g/ml) led to blockade of nuromus-cular transmission.

Effect of Soman on the Neuro-muscle Junctional and Extrajunctional Nicotinie Acetylcholine Receptors / 第二军医大学学报

Autoradiography of nicotinic acetylcholine receptors (N-AChR) with the application of histochemical staining location of cholinesterase was used to observe the effect of soman on junctional and extrajunctional N-AChR. Testing with the diaphragms and extensor digitorum longus muscles of mice and rats, we found that soman mainly increased the number of extrajunctional N-AChR. It did pot alter the number of junctional N-AChR significantly, nor did it have any pronounced effects on the glycoprotein property and isoelectric point (pI) of junctional and extrajunctional N-AChR. The change of extrajunctional N-AChR number caused by soman is similar to the phenomenon of increased extrajunctional N-AChR number and sensitivity resulting from denervation, but the mechanism of action is different from the latter. The increase of N-AChR number is one of the important characteristics of soman poisoning which make it different from other nerve agents. To maintain the metabolic balance of N-AChR may be an important new approach to the treatment of soman poisoning.

EFFECTS OF SOME DRUGS ON THE TURNOVER OF NICOTINIC ACETYLCHOLINE RECEPTOR / 第二军医大学学报

The present study describes the effects of carbamate anti-cholinesterase agents and other drugs on the binding sites and on the turnover of nicotinic acetylcholine receptors (N-AChR). The direct binding studies with 125I-?-Bungarotoxin have shown that the neostigmine, prostigmine, pyridostigmine, and ambenonium specifically blockada the N-AChR binding sites, but physostigmine has no directly effect on the N-AChR binding sites.Small dose of ambenomine increases degradation rate of surface N-AChR and it decreases the rate of new N-AChR incorporation into membrane. The bindings of sodium phenobabital to N-AChR sites are very similar to those of d-tubocurarine. The parathion(E605)has no direct bindes to N-AChR sites. The density of extrajunc-tional N-AChR sites is increased and the RBI is 1.46.

The Effects of Carbamates and Soman on the Metabolism of Nicotinic Acetylcholine Receptors in Cultured Skeletal Muscle Cells / 第二军医大学学报

The effects of carbamates and soman on the metabolism of nicotinic acetylcholine receptors (N-AChR) in cultured skeletal muscle cells were studied by 125I-a-bungarotoxin (125I-a-BTX), a specific marker. It was indicated that N~AChR degradation process was inhibited and the incorperation rate of IshAChR and the number of N~AChR in the surface of the cell membrane were increased 4h after prertreatment of high concentrations of carbamates. The number of N-AChR was also increased after pre-treatment of low concentrations of soman, whose effects on N-AChR metabolism were similar to those of high concentrations of carbamates. The incorperation rate of N-AChR was observed by inhibiting the protein synthesis with puromysin, suggesting that soman may increase the number of N-AChR by increasing the incorperation of N-AChR instead of increasing the synthesis of N-AChR.

STUDIES OF ISOLATION, PURIFICATION AND IODINATION OF ?-BUNGAROTOXIN / 第二军医大学学报

The isolation purification, iodination and identification of a-Bungarotoxin(a-BTX)were recorded.Purified a-BTX was prepared from the venom of Hunan Bu-ngarus multicinctus (Blyth) by CM-Sephadex C~50 ionexchange chromatography and Sephadex G~25 chromatography.The homogeneous a-BTX was obtained by rechromatography of purified ct-BTX (fraction 3) on a CM-Cellulose CM-32, and was labelled with 1251 by chloramine-T method.The 1251-?-BTX was then separated from Na125I and purified by Sephadex G-25 column.The results yield a specific activity of 90~100 Ci/mM.40~50% labelling.40~60% recovery of protein and less than 3 % contamination with free iodine in 125I-?-BTX.The purified a-BTX was identified by determining its N-terminal amino acid, amino acid composition, isoelectric and polyacrylamide gel electrophoresis.Biological activity of the ?-BTX was determined by its toxicity to mice, its neuromuscular blocking action and binding to acetylcholine receptors at the motor entplate of the rat diaphragm.