Chromatographic separation of the venom of Bungarus multicinctus and characterization of its components

Prednisone-neostigmine interactions at cholinergic junctions

The effect of corticosteroid (prednisone) and/or chronic anticholinesterase (neostigmine) treatment on alpha-bungarotoxin binding was examined in the diaphragms of male rats. In endplate regions of the diaphragm, prednisone treatment had no effect on the density of toxin binding sites, either when given alone or when administered in conjunction with neostigmine while neostigmine was observed to reduce specific binding to less than half after one week.

Comparison of Bungarus caeruleus venom with the venom from which a putative cholinergic ionophore marker was isolated

Comparisons are described between Bungarus caeruleus venom and the actual venom from which a putative marker for the cholinergic ionophore, called ceruleotoxin, was isolated. The venoms are shown to be different by two procedures for ion exchange chromatography and by isoelectric focusing on polyacrylamide gel. The activities of the purified "ceruleotoxin" as an inhibitor of acetylcholine receptor-mediated ion flux and as a phospholipase have been reported (Bon & Changeux, 1977b). The results reported herein suggest that this toxin is from an unknown origin.

Characterization of an 11,000-dalton beta-bungarotoxin: binding and enzyme activity on rat brain synaptosomal membranes

The binding and phospholipase A2 activity of an 11,000-dalton beta-bungarotoxin, isolated from Bungarus multicincutus venom, have been characterized using rat brain subcellular fractions as substrates. 125I-labeled beta-bungarotoxin binds rapidly (k = 0.14 min-1 and 0.11 min-1), saturably (Vmax = 130.1 +/- 5.0 fmoles/mg and 128.2 +/- 7.1) fmoles/mg), and with high affinity (apparent Kd = 0.8 +/- 0.1 nM and 0.7 +/- 0.1 nM) to rat brain mitochondria and synaptosomal membranes, respectively, but not to myelin. The binding to synaptosomal membranes is inhibited by divalent cations and by pretreatment with trypsin. The binding results suggest that the toxin binds to specific protein receptor sites on presynpatic membranes. The 11,000-dalton toxin rapidly hydrolyzes synaptosomal membrane phospholipids to lysophosphatides and manifests relative substrate specificity in the order phosphatidyl ethanolamine greater than phosphatidyl choline greater than phosphatidyl serine. These results indicate that the 11,000-dalton beta-bungarotoxin is a phospholipase A2 and can use presynaptic membrane phospholipids as substrates. The binding, phospholipase activity and other biological properties of the 11,000-dalton toxin are contrasted with those of the beta-bungarotoxin found in highest concentration in the venom (the 22,000-dalton beta-bungarotoxin), and the two toxins are shown to have qualitatively similar properties. Finally the results are shown to support the hypothesis that beta-bungarotoxins act in a two-step fashion to inhibit transmitter release: first, by binding to a protein receptor site on the presynatic membrane associated with Ca2+ entry, and second, by perturbing through enzymatic hydrolyses the phospholipid matrix of the membrane and thereby causing an increase in passive Ca2+ permeability.

Purification and biochemical characterization of an 11 000-dalton beta-bungarotoxin

The chromatographic separation and biochemical characterization of a beta-bungarotoxin is described. This toxin is isolated as the most basic eluting protein of Bungarus multicinctus venom when separated by column chromatography on CM-Sephadex C-25. The protein migrated as a single band on pH 4.3 and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The molecular weight of this toxin was estimated to be 10 000 +/- 1000 by analytical sedimentation analysis. This value was consistent with the electrophoretic mobility of the toxin in SDS-polyacrylamide gels. The amino acid composition of this 11 000-dalton beta-bungarotoxin was similar to that of the 22 000-dalton beta-bungarotoxin previously reported (Lee et al. (1972) J. Chromatogr. 72, 71--82; Kelly, R.B. and Brown, III, F.R. (1974) J. Neurobiol. 5, 135--150; Kondo et al. (1978) J. Biochem. Tokyo 83, 91--99), suggesting that the 11 000-dalton toxin may be one of the polypeptide chains of the larger toxin. The 11 000-dalton beta-bungarotoxin was toxic to mice when injected intravenously. Animals that received lethal doses exhibited hyperexcitability followed by ataxia, convulsions, and death. The minimum lethal dose was 0.12 microgram/g body weight. This beta-bungarotoxin exhibited Ca2+-dependent phospholipase A activity comparable to that of the 22 000-dalton beta-bungarotoxin. The enzyme exhibited phospholipid substrate specificity in the rank order of phosphatidyl-choline, phosphatidylserine, phosphatidylethanolamine, and phosphatidyl-inositol. The enzyme activity was destroyed by boiling for 3 min at pH 8.6. In addition, an enzymatically inactive quantity of the 11 000-dalton toxin, equivalent to five times the minimum lethal dose of enzymatically active toxin, was not lethal when injected into mice. To test whether phospholipase A activity is responsible for lethality, bee venom phospholipase A2 was injected into mice at similar and greater concentrations with no toxic effect. Thus, while phospholipase A activity may be required for the lethal effect of the 11 000-dalton beta-bungarotoxin, the specificity of action of the toxin is not determined by its enzyme activity.

Metabolism of acetylcholine receptor in chick embryo muscle cells: effects of RSV and PMA

We have investigated some aspects of the metabolism of the integral membrane protein acetylcholine receptor (AChR) in normal and transformed cultures of chick embryo muscle cells. Turnover of AChR in control muscle cell cultures was compared with turnover in cultures infected and transformed by a temperature-sensitive mutant of Rous sarcoma virus (RSV) and with cultures treated with the tumor promoter phorbol myristate acetate (PMA). The parameters of AChR metabolism were estimated using 125I-alpha-bungarotoxin as a stoichiometric high affinity ligand for the AChR. We found that both RSV transformation and PMA increased the rate of degradation and decreased the rate of synthesis of AChR. The consequent reduction in steady state receptor levels suggests that oncogenic transformation and tumor promoter significantly alter the metabolism of cell surface membranes. We also observed that parameters of AChR metabolism in control cultures changed systematically in a pattern which depended upon the age of the culture as well as the use of embryo extract or fetal bovine serum as medium supplements. The muscle cell system allows quantitative measurement of an integral membrane protein and its metabolism, and may serve as a more general model for alterations in membrane and surface receptor metabolism associated with the transformed state.

beta-Bungarotoxin. Separation of two discrete proteins with different synaptic actions

beta-Bungarotoxin, a specific presynaptic blocking agent, was prepared in two stages from the crude venom of Bungarus multicinctus by ion-exchange chromatography on the weakly acidic ion exchanger, CM-Sephadex, and on the strongly acidic ion exchanger, sulphopropyl-Sephadex. By these procedures it was purified to a single protein, which was shown by reduction to contain two polypeptide chains with mol.wts. of less than 15000. During purification of beta-bungarotoxin three other proteins were isolated. Two of these proteins have similar molecular weights, subunit structure and physiological properties to the major protein component. This latter is referred to as beta-bungarotoxin, since it has the same physiological properties as those described for unpurified beta-bungarotoxin by other workers. The first protein has very different physiological effects and biochemical properties from beta-bungarotoxin. This protein has a single class of polypeptide chains with an apparent molecular weight that is lower than the main beta-bungarotoxin protein, and appears to block synaptic transmission by a predominantly postsynaptic effect. It has been suggested [Oberg & Kelly (1976) J. Neurobiol. 7, 129-141] that the action of beta-bungarotoxin depends on its phospholipase A activity; however, in this preparation of the toxin less than 50 muunits of phospholipase A activity were detected (1 unit of activity is the amount of enzyme forming 1 mumol of L-alpha-phosphatidylcholine/min per mg of protein).

Intrathymic pathogenesis of myasthenia gravis: transient expression of acetylcholine receptors on thymus-derived myogenic cells

Differentiation of myogenic stem cells from undifferentiated thymic stem cells is thought to play a critical role in the pathogenesis of myasthenia gravis. The expression of membrane acetylcholine receptor (AChR) on the membranes of developing muscle clones in cultures of murine thymus reticulum was followed and found to be transient. AChR are first expressed shortly after fusion of myotubes. In subsequent stages of myogenic development, the density of homogenously distributed AChR is strongly increased, and, in addition, concentrated "hot spot" AChR areas appear. During further maturation, membrane AChR are lost. Highly mature myotubes (3 months in culture) lack substantial amounts of homogenous AChR, as well as hot spots.

Neurotoxins of Bungarus multicinctus vernom. Purification and partial characterization

The purification to homogeneity of nine neurotoxic components of the venom of Bungarus multicinctus is described. The purified components include alpha-bungarotoxin and two other alpha-type synaptic toxins and beta-bungarotoxin and five other beta-type synaptic toxins. The purified toxins have been characterized by electrophoresis, isoelectric focusing, amino acid analysis, and N-terminal amino acid determination. The alpha-type synaptic neurotoxins constitute a discrete class with molecular weights of 7000-8500, isoelectric points (pI) of 9.0-9.2, and N-terminal isoleucine or methionine. The beta-type synaptic neurotoxins constitute a second group with molecular weights of 20 000-22 000 and pI = 8.8-9.7. Fractions 10 through 13 exhibit a chain structure consisting of a 6000-7000 light chain and a 11 000-15 000 heavy chain apparently covalently stabilized by interchain disulfides. Fractions 9A and 14 were single chains of 11 000-14 000 which resemble the sequenced beta-type synaptic neurotoxin notexin (Halpert, J., and Eaker, D. (1975), J. Biol. Chem. 250, 6990). All of the beta-type synaptic toxins have a single tryptophan and N-terminal aspartic acid or asparagine.

Isolation and characterization of presynaptically acting neurotoxins from the venom of Bungarus snakes

1. Five presynaptic toxins have been isolated in pure form from the venom of Bungarus multicinctus and Bungarus caeruleus and named beta1, beta2, beta3, beta4, and beta-ceruleotoxin. 2. They differ in electrophoretic mobility and amino acid composition, while all have the same molecular weight (22000) and are composed of two subunits of molecular weight 9000 and 12000. 3. The toxins have phospholipase A activity when assayed with both natural and synthetic phospholipids, and this activity requires the presence of Ca2+ ions. 4. beta-Bungarotoxin (beta3) binds 1 mol of Ca2+ per mol of protein and this binding induces a conformational change as detected by fluorescence measurements in the presence of the dye 8-anilino-1-naphthalene sulfonic acid. 5. The phospholipase activity of all the toxins is lost when a critical histidine residue is modified with p-bromophenacyl bromide. 6. As a result of the modification the lethality of the toxins is greatly reduced. 7. Native toxin causes a rapid decrease in amplitude of end-plate potentials, followed by a transient increase and subsequent decrease, until transmitter release is completely abolished. The modified toxin still causes the early decrease in release but toxin action does not progress to complete block. 8. The rate of blockage of transmitter release by native toxin is reduced in the presence of modified toxin. 9. It is concluded that phospholipase activity plays an important role in the action of this class of toxins at the neuromuscular junction.

Effects of Sr2+ and Mg2+ on the phospholipase A and the presynaptic neuromuscular blocking actions of beta-bungarotoxin, crotoxin and taipoxin

1.beta-Bungarotoxin, crotoxin and taipoxin, presynaptic neurotoxins of snake venom origin, have about the same phospholipid-splitting activities as a much less toxic cobra phospholipase A2 in the presence of Ca2+ and deoxycholate. 2. Sr2+ was a much less effective activator of the enzymes than is Ca2+, the activation by Sr2+ being only 3-6% for beta-bungarotoxin and crotoxin and 12% for taipoxin. 3. Sr2+ also inhibited the Ca2+ -activated enzymes by 80% in the cases of beta-bungarotoxin and crotoxin, but only 16% in the case of taipoxin. 4. Mg2" had no significant effect on beta-bungarotoxin or crotoxin, but activated taipoxin in the presence or absence of Ca2". 5. In Sr2+ -Tyrode lacking Ca2+ all three toxins exhibited the same immediate depression followed by facilitation in the rat and mouse diaphragms, but the final blocking activity was only 3-10% with beta-bungarotoxin and crotoxin and was 30% with taipoxin. 6. In Sr2+ -Tyrode, increasing in the rate of nerve stimulation had less accelerating effect on the development of neuromuscular block than in Ca2+ -Tyrode for any of the toxins. 7. Removal of Mg2+ from Sr2+ -Tyrode did not diminish the potency of taipoxin in blocking neuromuscular transmission, suggesting that enzyme activity at the outer surface of the axolemma does not contribute to the neuromuscular blocking action. 8. All of the results indicate that there are close correlations between the presynaptic activities of these toxins and their phospholipid-splitting activities in the cationic environment prevailing in the axoplasm. Apparently the final blocking effect of these toxins is due to phospholipase A action within the nerve terminal.

Study of two different subpopulations of anti-acetylcholine receptor antibodies in a rabbit with experimental auto-immune myasthenia gravis

Two different subpopulations of anti-acetylcholine receptor antibodies were studied during the evolution of experimental autoimmune myasthenia in one rabbit immunized with Torpedo acetylcholine receptor. The results show that the subpopulation of antibodies directed against the toxin-binding site of the receptor might play a role in the appearance of the paralysis observed in this particular case.

Discrimination between nicotinic receptors in vertebrate ganglia and skeletal muscle by alpha-bungarotoxin and cobra venoms

1. We have used snake neurotoxins, alpha-bungarotoxin and venoms from Naja naja siamensis and Naja nivea, to distinguish the nicotinic receptors of ganglia from those of skeletal neuromuscular junctions. 2. These neurotoxins failed to block responses of isolated guinea-pig longitudinal muscle with adherent myenteric plexus to the nicotinic agonists, nicotine or dimethylphenylpiperazinium, to acetylcholine (ACh), or to electrical field stimulation. 3. The toxins failed to affect responses of the isolated guinea-pig stomach to pregnaglionic stimulation by way of the vagus nerves or of the vas deferens to preganglionic stimulation via the hypogastric nerves. 4. Snake neurotoxins did not block non-adrenergic inhibitory responses of the rabbit small intestine to nicotine or electrical field stimulation. 5. Neurotoxins were ineffective blockers against nicotinic agonists in new-born rabbit or embryonic chick intestine. 6. Attempts to increase the penetration of the toxins into tissues with dimethylsulphoxide, exposure to hypertonic solutions, or to ethylene-diaminetetracetic acid did not enable the toxins to act as nicotinic antagonists. 7. In contrast to diaphragmatic or oesophageal skeletal neuromuscular junctions no binding of rhodamine or tritium labelled toxins to structures in ganglia could be detected. 8. No potential permeability barriers were found by electron microscopy of the ganglia of the guinea-pig myenteric plexus. 9. The tracers, lanthanum ion and ruthenium red, readily penetrated into all regions of the myenteric plexus including synaptic gaps. 10. It is concluded that the failure of snake neurotoxins to act as nicotinic antagonists or to bind to ganglia is not due to their inability to reach ganglionic nicotinic receptors. Therefore, it is likely that ganglionic nicotinic receptors are different from those of the skeletal neuromuscular junction.

Ceruleotoxin: a possible marker of the cholinergic ionophore

Ceruleotoxin, a toxin component of Bungarus caeuleus venom, blocks in vivo the depolarisation caused by carbamylcholine on the isolated electroplaque from Electrophorus electricus and in vitro in increase of 22Na+ and 42K+ efflux caused by cholinergie agonists on excitable receptor-rich microsacs prepared from Torpedo marmorata electric organ. However, at variance with the typical alpha-toxins, ceruleotoxin does not interfere with the binding of [3H]acetylcholine and of alpha-[3H]toxin to the cholinergic receptor site. Ceruleotoxin also slightly modifies 35SO 2 4-and [14C]glucose efflux. Some of its effects on the postsynaptic membrane may be related to the presence of a phospholipase activity present in the preparation and are discussed in those terms. It is proposed that ceruleotoxin selectively blocks the electrogenic action of acetylcholine on the postsynaptic membrane without binding to the cholinergic receptor site, and might serve as an useful tool to characterise the ion translocating device, the ionophore, associated with the cholinergic receptor site.

Relationship between the neurotoxicity and phospholipase A activity of beta-bungarotoxin

beta-Bungarotoxin is a protein neurotoxin that exhibits phospholipase A activity. The neurotoxin and phospholipase A activities were similarly affected by several agents that modify proteins in various ways. Both activities were very thermostable and resistant to treatment with proteases, 6 M urea, phenylmethylsulfonyl fluoride, and N-acetylimidazole. Both activities were sensitive to beta-mercaptoethanol, and to N-bromosuccinimide and ethoxyformic anhydride, which previously had been shown to inactivate rattlesnake venom phospholipase A by modifying selective amino acids. Dihexanoyllecithin, which acts as a substrate for the beta-bungarotoxin phospholipase A, and Ca2+ protect the phospholipase A activity against inactivation by ethoxyformic anhydride but not the neurotoxicity. Treatment of intact membranes with proteases reduces hydrolysis of the membranes lipids by the toxin phospholipase A.

Postsynaptic membranes in the electric tissue of Narcine: III. Isolation and characterization

Postsnyaptic membranes in homogenates of the electric tissue of Narcine were identified by labelling nicotinic acetylcholine receptors in the membranes with radioactive alpha-bungarotoxin. Various media and centrifugation conditions were examined in an attempt to obtain highly purified postsynaptic membranes. The main criterion for purification was approach towards the specific activity of the pure receptor protein, 9--10 nmol toxin-sites/mg protein. Isolation of tissue microsomes with Tris buffer, EDTA and the protease inhibitor phenylmethylsulfonylfluoride (PMSF), conditions which preserve the receptor molecules optimally, yielded about 50% of the tissue toxin-sites, 5% of the protein, 4% of the ATPase and less than 2% of the acetylcholinesterase (AChE). Further separation of vesiculated membranes in continuous density gradients of sucrose showed that the major contaminants of postsynaptic membrane vesicles were damaged mitochondria and tubular vesicles of dorsal electroplaque membranes rich in ATPase. Mitochondria were effectively removed from homogenates by 'differential' centrifugation, and ATPase-rich vesicles could be largely removed by causing their agglutination with calcium ions, or by controlled proteolysis in the absence of PMSF. Partially purified postsynaptic membranes were obtained having about 7 nmol toxin-sites/mg membrane protein. Further purification appears possible by affinity techniques.

Postsynaptic membranes in the electric tissue of Narcine: IV. Isolation and characterization of the nicotinic receptor protein

The nicotinic receptor protein of the electric tissue of Narcine was purified in several different media by partial isolation of postsynaptic membranes and affinity chromatography. Protease inhibitors were found to be necessary to prevent degradation of the protein, and both EDTA and Tris buffer were used in addition to prevent intramolecular crosslinking of 44,000 and 58,000 dalton subunits by tissue factors. The intact protein was found to have a molecular weight close to 400,000, and appears to be composed of four subunits of 44,000 daltons, two to three of 48,000, one of 58,000 and one of 65,000. All the subunits are glycoproteins and their amino acid compositions show similar hydrophobicity and acidity, suggesting similar positioning in postsynaptic membranes. Crosslinking experiments showed that acetylcholine and alpha-bungarotoxin bind to the smallest subunit, and suggest the juxtaposition of at least two of these subunits, and of all four toxin molecules bound to a receptor molecule. Morphological studies of the protein in membranes and after purification indicated cylindrial molecules with central cores.

Innervation of heart cells in culture by an endogenous source of cholinergic neurons

Hearts of embryonic mice 9 days in utero were found to have an endogenous source of cholinergic neurons which can survive in dispersed cell cultures. These neurons are electrically excitable, have ultrastructural characteristics of cholinergic embryonic neurons, and functionally innervate heart cells in culture. The nature of the innervation described is muscarinic cholinergic.

An autoradiographic analysis of [3H]alpha-bungarotoxin distribution in the rat brain after intraventricular injection

Purified alpha-bungarotoxin was isolated by chromatography and made radioactive with tritium ([3H]acetamidino-alpha-bungarotoxin). Infusions of [3H]alpha-bungarotoxin alone or preceded by tubocurarine or atropine were given into the third ventricle. 2. 12, or 24 h after injection the brains were prepared for autoradiography. Injections of alpha-bungarotoxin (radioinert) in buffer, or of [3H]parathyroid hormone in buffer, served as controls. The various patterns of labeling suggest the presence of nicotinic-cholinergic neurons within the arcuate and basolateral regions of the hypothalamus including the supraoptic and suprachiasmatic nuclei and, in addition, the central nucleus of the amygdala.

Lateral motion of fluorescently labeled acetylcholine receptors in membranes of developing muscle fibers

We have made direct, quantitative measurements of the lateral motion and age-dependent distribution of acetylcholine receptors (AChR) on the surface of rat myotubes in primary culture. AChR were fluorescently marked with tetramethylrhodamine-labeled alpha-bungarotoxin and AChR lateral motion was measured by the fluoresence photobleaching recovery technique. We found two coexisting distinct classes of AChR: (i) mobile, uniformly distributed AChR that appear on all myotubes shortly after fusion from myoblasts; and (ii) immobile, dense, highly granular AChR in patches of 10-60 mum size that appear shortly after fusion and disappear after myotubes have become extensively interconnected. In addition, evidence of turnover of AChR labeled with tetramethylrhodamine-alpha-bungarotoxin is seen in the gradual internalization of surface fluorescence within 36 hr after labeling. The relevance of these results to an understanding of the membrane dynamics and localization of muscle AChR is discussed.

Acute muscle denervation induced by beta-bungarotoxin

The neurotoxin, β-bungarotoxin (β-BuTX) purified from Bungarus multicinctus snake venom exerts various effects on frog and rat motor nerve terminals. Exposure to β-BuTX triggers, in the terminals, impulses which are rapidly distributed to the whole motor unit and elicit contractions of the muscle. β-BuTX raises the frequency of spontaneous release of acetylcholine quanta and inhibits the release evoked by nerve impulses, all of which leads to complete cessation of transmitter release. Subsequently, the motor axon disappears from the endplate and the Schwann cell establishes extensive synaptic contact with the muscle fibre. After only 30 min in β-BuTX, some endplates attain a stage of denervation similar to that seen several days after transecting the motor nerve. The neuromuscular effects of β-RuTX may result from its phospholipase activity and from an increase in the level of ionized calcium inside the terminals.

Snake venom toxins. Purification and properties of low-molecular-weight polypeptides of Dendroaspis polylepis polylepis (black mamba) venom

Twelve low-molecular-weight proteins, of which eleven have subcutaneous LD50 values of less than 40 mug/g mouse, were purified from Dendroaspis polylepis polylepis venom. Ion-exchange chromatography on Amberlite CG-50 and ion-exchange chromatography on carboxymethyl-cellulose and/or phosphocellulose was used for the purification. The amino-terminal sequences of these proteins were determined and used to indicate that five groups of low-molecular-weight polypeptides are to be found in black mamba venom. Proteins from two of these groups which have low toxicity individually, when used together show synergism, in that their toxicity in combination is greater than the sum of their individual toxicities.

Taipoxin, an extremely potent presynaptic neurotoxin from the venom of the australian snake taipan (Oxyuranus s. scutellatus). Isolation, characterization, quaternary structure and pharmacological properties

Taipoxin (taipan toxin), purified from the venom of the Australian taipan (Oxyuranus s. scutellatus) by gel filtration on Sephadex G-75 followed by column zone electrophoresis, is the most lethal neurotoxin yet isolated from any snake venom. The LD50 is 2 mug/kg in the mouse. The main physiological effect is a gradual reduction to complete stop of evoked and spontaneous release of acetylcholine from motor nerve terminals. Intoxicated animals die of asphyxia caused by neuromuscular blockage of the respiratory muscles. Taipoxin is a moderately acidic sialo-glycoprotein (pI 5) with a molecular weight of 45 600 as calculated from composition data or 46 800 as determined by meniscus depletion sedimentation equilibrium. Taipoxin is a 1:1:1 ternary complex of subunits designated alpha, beta and gamma which dissociate completely at low pH and high ionic strength or in 6 M guanidine hydrochloride. The dissociation by guanidine at neutral pH is reversible, while the acid-induced dissociation is not . The alpha and beta components consist of 120 amino acid residues cross-linked by seven disulfide bridges, whereas the gamma component has 135 residues and eight disulfides. The very basic (pI Greater than 10) alpha component contains 13 residues of arginine and is the only subunit displaying lethal neurotoxicity (mouse LD50 approximately 300 mug/kg). The neutral beta fraction was separated by ion-exchange chromatography into two iso-component, beta 1 and beta2, which differ slightly in amino acid composition. The very acidic gamma component contains all of the carbohydrate, which includes 4-5 residues of sialic aid. The three subunits are homologous in sequence although the gamma component is eight residues longer on the N-terminus and must also contain extra amino acids elsewhere.

Is the contractile response to exogenous acetylcholine due to a presynaptic effect?

Whether the contractile response induced by exogenous acetylcholine (ACh) chiefly involved the pre- or post-synaptic junctional site of the motor endplate was studied by using the cat gastrocnemius nerve muscle preparation poisoned with beta-bungarotoxin (beta-BuTX), a toxin isolated from the venom of Bungarus multicinctus which acts presynaptically. 2 After neuromuscular transmission was completely blocked by beta-BuTX, the dose-response curve of the contractile response induced by close intra-arterial injection of ACh, was compared with that of the control. No appreciable difference was observed. 3 In contrast, the response to ACh was completely abolished when neuromuscular transmission was blocked by alpha-bungarotoxin, a toxin isolated from the same venom which acts postsynaptically. 4 It is concluded that postjunctional site of the motor end-plate is chiefly involved in the contractile response produced by exogenous ACh.

Experimental myasthenia in Balb/c mice immunized with rat acetylcholine receptor from rat denervated muscle

A new model of an autoimmune disease of the neuromuscular junction was obtained by injection of acetylcholine receptor purified from rat denervated muscles into Balb/c mice. Anti-rat, then anti-mouse acetylcholine receptor antibodies, appear in mouse serum during the immunization procedure. Electrophysiological investigations performed on immunized mice reveal a neuromuscular block similar to that found in myasthenia gravis. Not a single mouse with objective signs of muscular weakness was lacking anti-mouse acetylcholine receptor antibodies but no correlation was found between their level and the severity of the disease.

Mechanism of action of beta-bungarotoxin on synaptosomal preparations

The neurochemical activity of beta-bungarotoxin was investigated using a synaptosomal preparation of rat cerebral cortices. In preparations preincubated with [3H]choline in order to label acetylcholine the toxin caused a rapid release of the transmitter, which was calcium dependent but only a little affected by a depolarizing concentration of potassium. beta-Bungarotoxin was also shown to be a potent inhibitor of the high affinity transport system for choline, producing 50% inhibition at a concentration of 50 nM. These findings explain the observed electrophysiological effects of the toxin. Electron microscopy revealed no discernible effect of 0.1 muM beta-bungarotoxin on either synaptic vesicles or mitochondria. Neither the release of transmitter nor the inhibition of choline uptake by the toxin was affected by the presence of an inhibitor of phospholipase activity.

Effects of alpha-toxins from Bungarus multicinctus and Bungarus caeruleus on cholinergic responses in Aplysia neurons

The effects of alpha-bungarotoxin from Bungarus multicinctus and Bungarus caeruleus were studied on three types of cholinergic response in Aplysia central neurones. These responses are the result of three distinct changes in ionic permeability: selective increases in permeabiliyt to Na, Cl and K, respectively. It was shown that 10(-5) M alpha-bungarotoxin from B. multicinctus completely blocks the response resulting from an increase in Cl permeability, while having no effect on either of the other two responses types (even when the toxin concentration was increased to 5 X 10(-5) M). The block of the Cl-dependent response by alpha-bungarotoxin is reversible. None of the three response types were affected by similar concentrations of alpha-toxin from B. caeruleus. Higher concentrations were not systematically tested. These results contradict reports of other authors on the action of alpha-bungarotoxin on molluscan acetylcholine (ACh) responses. Possible reasons for the discrepancies between our findings and those published by other authors are discussed.