Angela Vincent

Neuromuscular transmission after immunization against acetylcholine receptors

Injection of acetylcholine receptors from the electric organ of Torpedo into rabbits or rats, produces antibodies which bind to acetylcholine receptors in the muscle membrane or in solution. Binding of antibody to the receptors results in diminished acetylcholine sensitivity of the muscle fibres, reduced amplitude of miniature end-plate potentials, block of neuromuscular transmission and a decrease in the ability of the receptors to bind a-bungarotoxin. Antibodies raised against acetylcholine receptors from Torpedo cross-react with acetylcholine receptors from rabbit, rat and frog muscle.

Transmitter Release Induced by a 'Factor' in Rabbit Serum

Non-heated rabbit serum causes massive transmitter release from motor nerve endings. The effect is not observed after heating the serum, in the way usually done to destroy complement. It seems that serum may be acting on the nerve terminals by a mechanism involving the complement system in the absence of antibody.

Acetylcholine in human muscle

Intercostal muscle from patients with myasthenia gravis and from control patients without clinical signs of muscular disease was assayed for its acetylcholine content by means of gas chromatography/mass spectrometry. Apart from acetylcholine, no other similar compound was detected in the muscles. Myasthenic muscle contained about twice as much acetylcholine as control muscle, and the resting release of acetylcholine was approximately the same in both types of muscle.

The coupling of the adenylate kinase and creatine kinase equilibria. Calculation of substrate and feedback signal levels in muscle.

It has been estimated that the ratio of glycolytic flux in fully active muscle to that in resting muscle is in the region of 1,000 : 1 [I] . The flux is controlled partly by adrenaline, which acts through 3’,5’-cyclic AMP, and partly by feedback signals from the adenine nucleotide pool, the control in both cases being exerted by modifying the activity of glycogen phosphorylase (EC 2.4.1 .I) [2,3] and phosphofructokinase (EC 2.7.1 .I 1) [4,5]. The calcium release initiating muscular contraction may also play a part in activating glycogen phosphorylase [6]. One way in which the substrate and feedback signal levels have been investigated in muscle is by measurement of the total tissue levels of the various species under suitable physiological conditions; however, this method suffers from the disadvantage that it is difficult to take into account compartmentation of enzymes and substrates and binding of particular substrate species to proteins and other cellular components, and as a consequence, misleading conclusions may be drawn [71. This paper is concerned with an alternative approach to the study of substrate availability and feedback signals in muscle, namely the calculation of the concentrations of the various species during the progressive utilisation of creatine phosphate and ATP, assuming that the adenine nucleotides, creatine, and creatine phosphate are in their equilibrium concentrations as catalysed by the enzymes adenylate kinase (EC 2.7.4.3) and creatine kinase (EC 2.7.3.2). That this is a reasonable assumption is supported by the fact that when a muscle is stimulated, changes in adenine nucleotide

Characterization of an anti-fetal AChR monoclonal antibody isolated from a myasthenia gravis patient

We report here the sequence and functional characterization of a recombinantly expressed autoantibody (mAb 131) previously isolated from a myasthenia gravis patient by immortalization of thymic B cells using Epstein-Barr virus and TLR9 activation. The antibody is characterized by a high degree of somatic mutations as well as a 6 amino acid insertion within the VHCDR2. The recombinant mAb 131 is specific for the γ-subunit of the fetal AChR to which it bound with sub-nanomolar apparent affinity, and detected the presence of fetal AChR on a number of rhabdomyosarcoma cell lines. Mab 131 blocked one of the two α-bungarotoxin binding sites on the fetal AChR, and partially blocked the binding of an antibody (mAb 637) to the α-subunit of the AChR, suggesting that both antibodies bind at or near one ACh binding site at the α/γ subunit interface. However, mAb 131 did not reduce fetal AChR ion channel currents in electrophysiological experiments. These results indicate that mAb 131, although generated from an MG patient, is unlikely to be pathogenic and may make it a potentially useful reagent for studies of myasthenia gravis, rhabdomyosarcoma and arthrogryposis multiplex congenita which can be caused by fetal-specific AChR-blocking autoantibodies.

A Note on the Structure of Immunized Endplates

Neuromuscular junctions of rabbits immunized against acetylcholine receptors were examined with the electron microscope. Many endplates appeared normal, or showed changes which, by themselves, would not account for the blockage of neuromuscular transmission which develops after immunization. An unexpected organelle was found in the muscle fibres, associated with the endplate nuclei and the cytoplasm between them and the synaptic muscle membrane.