Abstract
IT has been postulated that the inhibitory post-synaptic potential in motoneurones is caused by the movement of ions across patches of the postsynaptic membrane that are momentarily (1–2 msec.) made very permeable for ions less than a certain critical size1. A sufficiently increased intracellular concentration of anions capable of passing through the postsynaptic membrane would change the normally hyper-polarizing inhibitory postsynaptic potential into a depolarizing one. In accordance with the hypothesis it was shown that injections of the small ions, Br−, Cl−, NO3−, and SCN−, but not injections of the large HCO3−, CH3CO2−, SO4−−, H2PO4− or HPO4−−, were effective in transforming the inhibitory postsynaptic potential into a depolarizing response. The diameter of the largest effective anion (derived from limiting ion conductances2 and expressed relative to K+= 1.00) was 1.11 and that of the smallest not effective, 1.65 (ref. 1). A weakness in the experimental evidence was the relatively few ions tested and the gap in size between the effective, and not effective, ions. Furthermore, it was not possible to exclude a slight effect of the bicarbonate ion (diameter 1.65) (ref. 1).
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References
Coombs, J. C., Eccles, J. C., and Fatt, P., J. Physiol., 130, 326 (1955).
Landolt-Boernstein, “Physikalisch-chemische Tabellen” (Julius Springer, Berlin, 1936). Robinson, R. A., and Stokes, R. H., “Electrolyte Solutions” (Butterworths Scientific Publications, London, 1959).
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ARAKI, T., ITO, M. & OSCARSSON, M. Anionic Permeability of the Inhibitory Postsynaptic Membrane of Motoneurones. Nature 189, 65 (1961). https://doi.org/10.1038/189065a0
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DOI: https://doi.org/10.1038/189065a0
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