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The article focuses on the on the safety standards for workers who work at heights. It relates the report from the 2008 Centers for Disease Control and Prevention (CDC) wherein a total of 11,303 Hispanic workers died from job-related injuries between 1992 and 2006 in the U.S. It discusses the protection standards provided by the U.S. Occupational Safety and Health Administration (OSHA) which include identifying fall hazards, covering floor holes, and inspection of fall protection equipment.

Neonatal mice resist the lethal effect of Waglerin-1. Because Waglerin-1 blocks the nicotinic acetylcholine receptor of mature end-plates, the appearance of lethality may result from the epsilon- for gamma-subunit substitution. In support of this hypothesis, adult knockout (KO) mice lacking the gene coding for the epsilon-subunit resist the lethal effect of Waglerin-1. In contrast, heterozygous litter mates respond to Waglerin-1 like adult wild-type mice. In vitro application of 1 microM Waglerin-1 inhibited spontaneous miniature end-plate potentials and evoked end-plate potentials of adult wild-type and heterozygous KO mice. Both miniature end-plate potentials and end-plate potentials of neonatal wild-type and adult homozygous KO mice resisted Waglerin-1. Waglerin-1 decreased the end-plate response of adult wild-type mice to iontophoretically applied acetylcholine (ACh) with an IC50 value of 50 nM; 1 microM Waglerin-1 decreased the ACh response to 4 +/- 1% of control for adult heterozygous KO mice. In contrast, 1 microM Waglerin-1 decreased the ACh response to 73 +/- 2% of control for wild-type mice less than 11 days old and had no effect on the ACh response of adult homozygous KO mice. Between 11 and 12 days after birth, the suppressant effect of Waglerin-1 on wild-type end-plate responses to ACh dramatically increased. Waglerin-1 reduced binding of alpha-bungarotoxin to end-plates of adult but not neonatal wild-type mice. These data demonstrate that Waglerin-1 selectively blocks the mouse muscle nicotinic acetylcholine receptor containing the epsilon-subunit.

A conjugate of alpha-bungarotoxin with horseradish peroxidase was used to visualize alpha-bungarotoxin binding sites at the fine structural level in isolated axonal membrane vesicles from lobster walking leg nerve. These plasma membrane vesicles have previously been shown to exhibit saturable binding of [3H]nicotine and [3H]acetylcholine. Binding of the toxin was identified in the axon plasma membrane and could be blocked by pretreatment with excess free alpha-bungaratoxin or d-tubocurarine. Binding sites for alpha-bungarotoxin were identified by the same technique in sections of intact nerve fibers from both lobster and spider crab and were found to be localized primarily in the axolemma rather than in the Schwann cell membrane.

The binding of alpha-bungarotoxin to several synthetic peptides comprising different segments of the region 173-204 of the alpha subunit of the Torpedo acetylcholine receptor was investigated to further localize the neurotoxin-binding site on the primary sequence. When tested in a solid phase microwell assay system, a 32-amino acid peptide corresponding to residues 173-204 (32-mer) bound 125I-alpha-bungarotoxin with the same affinity (4.2 x 10(-8) M as determined from IC50 values) as the isolated alpha subunit (4.6 x 10(-8) M). The relative affinities of other antagonists (alpha-cobratoxin, d-tubocurarine) maintained the same rank order in this assay system as has been demonstrated with the intact receptor. Agonists competed with binding of toxin at millimolar concentrations but lost all rank order of potency. These findings demonstrate that peptide 173-204 contains many of the antagonist-binding determinants present on denatured alpha subunit but has lost specificity of agonist binding. To further localize the toxin-binding site, alpha-bungarotoxin binding to seven shorter peptides corresponding to portions of the 32-mer was investigated. 125I-alpha-Bungarotoxin bound to alpha subunit peptides 179-192, 181-198, 185-196, 186-196, and 193-204, but not to alpha subunit peptides 173-180 and 194-204. In a second assay, all of the peptides competed with binding of 125I-acetylcholine receptor to immobilized alpha-bungarotoxin. The apparent affinity was highest for the 173-204 32-mer (1.4 x 10(-7) M) and lowest for peptides 173-180 and 194-204 (greater than 10(-4) M). The affinity of the other peptides was intermediate (approximately 10(-5) M) and about 100-fold less than that of the 32-mer. The affinity of alpha-bungarotoxin was 3.5 x 10(-10) M, of isolated, native acetylcholine receptor, 3.2 x 10(-9) M, and of isolated denatured subunit, 1.2 x 10(-8) M, with this assay. The retention of some toxin-binding capacity by the shorter peptides indicates toxin-binding determinants are distributed over the entire length of the 32-mer. The determinants with higher affinity are located in the central region of the 32-mer between residues 179 and 196.

The localization of acetylcholine receptors (AChR) in the surface of developing myogenic cells of the chick embryo anterior and posterior latissimus dorsi muscles in relation to the process of innervation has been studied at the ultrastructural level utilizing a horseradish peroxidase-alpha-bungarotoxin conjugate. Localized concentrations of AChR were found in small regions 0.1-0.4 micron in width on the surface of myogenic cells of 10- to 14-d-old muscles. Surface specializations consisting of an external coating of extraneous material and an internal accumulation of dense material are associated with the plasma membrane in the regions of AChR concentration. As the muscle fibers are innervated, reactive surface patches are found at the region of contact of the growing nerve fiber and the surface of myotubes or their fusing myoblasts. After the establishment of contact, the patches of reaction product become more numerous and coextensive within the region of the neuromuscular junction and its immediate surroundings forming a dense continuous deposit on the postsynaptic sarcolemma. Activity becomes increasingly restricted to the site of the neuromuscular junction as the embryos approach hatching. At all stages, specializations external and internal to the plasmalemma are found at regions of high density of AChR, suggesting that they play a role in the maintenance of a higher concentration of receptors at these sites. These specializations also occur at the region of initial synaptic contact, indicating that they might be recognized by the nerve and represent preferred sites of innervation. Innervation appears to exert a stabilizing influence on the area of high AChR concentration in contact with the nerve and to induce a further increase in the AChR density of this site while the number of AChR in the remaining portions of the muscle surface declines.

A region of the alpha subunit of the nicotinic acetylcholine receptor containing the alpha-bungarotoxin-binding domain was mapped on the primary amino acid sequence in relation to asparagine-141, the presumed site of N-linked glycosylation. Proteolytic fragments of the alpha subunit, immobilized onto positively charged membrane filters, that bind 125I-labeled bungarotoxin were further analyzed on the basis of the size of the fragments and the presence of asparagine-141 as determined by susceptibility to digestion with endoglycosidase H. The bungarotoxin-binding site was found not to reside between amino acid residues 1 and 140 since bungarotoxin-binding fragments that are considerably larger than 140 amino acids and lack N-linked oligosaccharide chains were detected. The size of the smallest bungarotoxin-binding fragment containing asparagine-141 and the size of fragments produced by digestion with V8 protease further indicated that the bungarotoxin-binding site is contained within amino acid residues 153-241. A 32-amino acid synthetic peptide comprising a portion of this region (residues 173-204) was tested for its ability to bind 125I-labeled bungarotoxin. 125I-labeled bungarotoxin bound to the peptide and was competed by unlabeled bungarotoxin and d-tubocurarine with IC50 values of 0.5 microM and 2 mM, respectively. We conclude that a major determinant of the bungarotoxin-binding site on the alpha subunit resides between residues 173 and 204.

The direct binding of alpha-bungarotoxin to the alpha subunit of the acetylcholine receptor from Torpedo electric organ immobilized onto protein blots was demonstrated. Protein blots were prepared by electrophoretically transferring resolved acetylcholine receptor subunits from 10% polyacrylamide gels onto Zetabind, positively charged nylon membrane filters. Such blots, when incubated with 125I-labeled alpha-bungarotoxin, washed, and autoradiographed, gave rise to a single labeled band corresponding to the alpha subunit of the receptor. The labeling with alpha-bungarotoxin could be inhibited by pretreating the receptor-containing membranes with the affinity ligand 4-(N-maleimido)-alpha-benzyltrimethylammonium iodide. In addition, the association of toxin with the alpha subunit could be inhibited by d-tubocurarine (IC50 = 0.9 mM). Furthermore, removal of high-mannose oligosaccharide chains from the alpha subunit by treatment with endoglycosidase H did not interfere with the observed toxin binding. Thus it is demonstrated that isolated, immobilized alpha subunit of the Torpedo acetylcholine receptor can bind alpha-bungarotoxin. However, the observed binding of alpha-bungarotoxin to immobilized alpha subunit is reduced in affinity to 1/1,000 to 1/10,000 of that obtained with native receptor. The endoglycosidase H-susceptible oligosaccharide side chain(s) is not required for this interaction. Binding of alpha-bungarotoxin is to the physiologically relevant acetylcholine binding site as defined by affinity ligand alkylation.

The localization of cholinergic receptors in brain synaptosomes and in synapses of the midbrain reticular formation and hypothalamic preoptic nucleus has been demonstrated by means of a horseradish peroxidase-alpha-bungarotoxin (HRP-alpha-Btx) conjugate. Only a small proportion of the total number of synapses was reactive. Axon terminals of reactive synapses contained primarily small clear vesicles, while synapses characterized by large numbers of dense core vesicles were unreactive. Toxin-binding sites were found to occur in a thickened zone of the postsynaptic surface. This procedure can be employed to study the regional distribution and localization of nicotinic receptor sites in the central nervous system.