The effects of a myasthenic serum on the acetylcholine receptors of C2 myotubes. I. Immunological distinction between the two toxin-binding sites of the receptor

We have examined the effect of a serum from a patient with myasthenia gravis on the binding of alpha-bungarotoxin (alpha-BuTx) to the acetylcholine receptors (AChRs) of a mouse muscle cell line, C2. After a 2-hr incubation, antibodies in the serum reduced toxin binding to C2 myotubes to a maximal extent of approximately 50%. The degradation of surface AChRs could account for the loss of only 5% of sites during the incubation; the remainder, therefore, must have been lost by blockage of binding. To investigate whether the antibodies blocked specifically one of the two toxin-binding sites that each AChR possesses, we used an analysis based on that of Sine, S. W., and P. Taylor, [1981) J. Biol. Chem. 255: 10144-10156). Although the two sites could not be distinguished by their rates of binding of alpha-BuTx, d-tubocurarine (dTC) inhibition of the initial rate of toxin binding revealed that the sites had affinities for dTC that differed by approximately 30-fold. Incubation with the myasthenic antibodies reduced the number of high affinity dTC sites, without affecting those of low affinity. We conclude that the two toxin-binding sites of the AChR are immunologically distinct.     

Organization of the posterior dorsal thalamus of the hedgehog

A study of the responsiveness of single neurons in the hedgehog thalamus to sensory stimulation was undertaken with the hypothesis that modality specific relay nuclei characteristic of the mammalian thalamus differentiate out of a pool of multisensory neurons. Support for this hypothesis was obtained in earlier investigations of the opossum thalamus. In some ways the hedgehog may be an even better representative of a primitive stage of thalamic development. For example, there is very little structural difference between the ventroposterior nucleus and the medial geniculate body. The results of the present microelectrode investigation showed that neither the ventroposterior nucleus nor the medial geniculate body was modality specific. Further, many neurons in the ventroposterior nucleus showed wide receptive fields characteristic of the posterior group of nuclei in cats. This finding of convergence of sensory input upon single neurons of the dorsal thalamus in a generalized mammalian type suggests that the specificity characteristic of higher mammals is a product of an evolutionary trend. Thus comparative neurology provides additional evidence that precise receptive fields must play an important role in behavioral adaptation.     

255. Energiestoffwechsel und Elektrolytveränderungen im Myokard der Ratte nach hypotfiermer Konservierung und in der Erholung

Zusammenfassung Das Ausmaß metabolischer Veränderungen nach einer 4stündigen Konservierung bei 2° C und ihre Reversibilität während anschließender parabiotischer Perfusion bei 37° C wurden in 180 Rattenherzen durch Bestimmung der energiereichen Phosphate und der Gewebswasser- und Elektrolytgehalte untersucht: 1. Kontinuierliche aerobe Perfusion mit oxygenierter Ringer-Lösung erhält nahezu normale Werte des Energiestoffwechsels am Ende der Konservierung, führt aber zu einer Schwellung mit einem Anstieg des Gewebsnatriums auf 300°/u und einem Abfall des Kaliums auf 70°/u. Während anschließender Hämoperfusion bewirkt dieses Ödem eine eingeschränkte Organdurchblutung und Gewebshypoxie. 2. Perfusion mit Nz äquilibrierter Ringer-Lösung vermindert gegenüber der aeroben Perfusion die Reserven an energiereichem Substrat, produziert aber kein stärkeres Ödem. Addition von Hypoxie und Schwellung bedingt die schlechteste Erholung in dieser Gruppe. 3. Nach einfacher hypothermer Lagerung bei 2° C findet sich das größte energetische Defizit, jedoch die geringste Wasseraufnahme und die beste Erholung der Substrat- und Elektrolytveränderungen. 4. Zwischen Kaliumverlust und Wasseraufnahme in allen Gruppen besteht eine lineare Beziehung, die mit zunehmender Schädigung und während Erholung in beiden Richtungen durchlaufen wird.

---

Energy metabolism and electrolyte changes in the myocardium of rats after hypothermic preservation and during recovery

Summary The extent of metabolic changes after 4 h preservation at 2° C and their reversability during subsequent parabiotic perfusion at 37° C were examined in 180 rat hearts by determining high-energy phosphates and the tissue fluid and electrolyte contents. 1. Continuous aerobic perfusion with oxygenated Ringer's solution produces nearly normal energy metabolism values at the end of preservation but leads to swelling with a rise of tissue sodium to 300% and a fall of potassium to 70%. During subsequent hemoperfusion this edema causes a restriction of organ perfusion with tissue hypoxia. 2. Perfusion with N₂-equilibrated Ringer's solution, compared with aerobic perfusion, reduces the reserves of energy-rich substrates but does not produce more edema. The combination of hypoxia and swelling produces the poorest recovery in this group. 3. After simple hypothermic storage at 2° C we find the greatest energy deficit but the lowest water retention and the best recovery of substrate and electrolyte changes. 4. Between potassium loss and water retention there is in all groups a linear relation which is maintained both with increasing damage and during revocery.