Fluorescent staining of acetylcholine receptors in vertebrate skeletal muscle

1. alpha-Bungarotoxin was labelled with fluorescent dyes and used as a stain for visualizing the distribution of acetylcholine receptors in vertebrate skeletal muscle fibres.2. Dye-toxin conjugates had the same pharmacological properties as native toxin, but their potencies were lower.3. Fluorescent staining was examined in teased muscle fibres. The stain was found to be confined to the neuromuscular junction and associated with the subsynaptic membrane.4. Staining intensity was reduced by curare and even more so by carbachol, but not by atropine or neostigmine. Pre-treatment of muscles with unlabelled alpha-bungarotoxin entirely prevented staining.5. The staining at amphibian neuromuscular junctions was characterized by a pattern of intense transverse bands occurring at intervals of approximately 0.5-1 mum, with fluorescence of lower intensity between them. Fluorescent staining was not detected on adjacent, extrasynaptic, muscle membrane. In side views the staining appeared as a fine line with small protuberances occurring at the same intervals as the intense bands seen face-on. These results indicate that acetylcholine receptors are associated with the entire subsynaptic membrane, including the membrane of the junctional folds and that their density changes abruptly at the border between synaptic and extrasynaptic muscle membrane.

An ultrastructural study of endotoxin induced damage in rabbit mesenteric arteries

Mesenteric arteries from control and endotoxin-treated rabbits were studied by electron microscopy. Animals were injected intracardially with an LD₅₀ dose of Escherichia coli endotoxin or saline 3 and 24 hr before being killed. Vessels were perfused with buffered glutaraldehyde before removal.

In control arteries endothelial cells were thin except in the nuclear region. Vesicles and caveolae were abundant in the cytoplasm. Few mitochondria, scanty endoplasmic reticulum and Golgi apparatus, free ribosomes, and glycogen granules were scattered in the cytoplasm. The endothelial cells rested on a basement membrane which was closely apposed to the internal elastic lamina. The medial smooth muscle layer contained many collagen fibres.

Endothelial cells from endotoxin-treated animals revealed extensive degeneration of subcellular organelles with only the vesicles and caveolae remaining intact. Ruptured mitochondria, areas of cytolysis and large vacuoles were prominent. The nucleus was often spindle shaped or tortuous in outline and sometimes exhibited vacuolization. Swelling and protrusion of endothelial cells into the lumen, the detachment of these cells from the internal elastic lamina, and the marked thickening of the internal elastic lamina were also prominent. Vascular endothelium reacts to histamine, serotonin, epinephrine and norepinephrine in a similar manner, suggesting that the effects observed after the administration of endotoxin may be due to the release of such chemical mediators. This study cannot differentiate between direct and indirect damage; however, it shows that bacterial endotoxin induces severe damage to continuous endothelium and internal elastic lamina.

The relative supply of carbohydrate and nitrogen to wheat grains, and an assessment of the shading and defoliation techniques used for these determinations

Leaf contribution to grain dry weight and grain nitrogen was estimated in four varieties of wheat from their responses to shading and defoliation treatments. The relation between movement of nitrogen and dry material from leaves to grains appeared as an important factor in the differences between varieties in respect to the percentage nitrogen content of grains. Experiments with labelled carbon, however, showed that there was a significant redistribution of assimilates from other parts when the ear was shaded or the flag leaf removed.

The role of the leaves in the accumulation of nitrogen by wheat during ear development

When wheat plants were deprived of nitrogen in the rooting medium at anthesis there was a small, but significant, increase in the nitrogen content of the grain at maturity. It was shown that there was a greater migration of nitrogen from the leaves and stem to the ear in plants deprived of nitrogen than in those plants supplied with nitrogen throughout ear development. In an examination of the effects on grain nitrogen content of leaf removal at anthesis, it was shown that this treatment reduces the uptake of nitrogen into the culm and the nitrogen content of the grain at maturity. Ear shading treatments significantly reduced the total nitrogen content of the grain in one experiment. Ear shading also decreased the amino nitrogen, and increased the nitrate nitrogen, content of the ear. Variation of the grain dry weight per ear, induced by shading, by defoliation treatments, or by differences in variety, were positively correlated with grain nitrogen content. Either the movement of dry matter and nitrogen into the ear are interdependent, or they are both promoted by some external factor, such as rate of growth of the ear. The possible importance of the leaves of the wheat plant in promoting the uptake of nitrogen into the culm and in supplying nitrogen to the grain is discussed.