Abstract
There are three classes of spontaneous miniature endplate potentials (MEPPs) in the normal vertebrate preparation and the ratios vary during synaptogenesis and with various treatments. In the unstressed adult preparation (frogs and mammals) most MEPPs (96%) contribute to a bell-shaped distribution (bell-MEPPs) which has a coefficient of variance of about 30% (Fatt and Katz, 1952). Del Castillo and Katz (1954) showed that the unitary evoked potentials are the same size as MEPPs and they proposed that the larger endplate potentials are composed of quanta the size of MEPPs. Liley (1956) and Boyd and Martin (1956) published amplitude histograms of small endplate potentials that were reduced with a low calcium-high magnesium saline that have distinct peaks that are integral multiples of the mean MEPP. These results. show that both spontaneous and evoked release are from the same pool of quanta. With conditions of low quantal content or with relatively low rates of spontaneous release the size of a quantum remains very constant (Katz, 1978). However, with high rates of evoked release (Kriebel, 1978) or induced spontaneous release, the average MEPP is greatly reduced (Kriebel and Gross, 1974; Kriebel and Stolper, 1975; Kriebel, et al., 1976; Kriebel and Florey, 1983; Kriebel and Pappas, 1987). These changes reflect differences in the ratio of two classes of MEPPs that are found in the normal preparation; and, do not usually reflect a change in the percentage of giant MEPPs as found with chronic botulinum toxin poisoning (see Thesleff and Molgó, 1983, for a review).
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© 1988 Plenum Press, New York
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Kriebel, M.E. (1988). Quantal Classes and Subunits of Quanta in the Neuromuscular Junction. In: Grinnell, A.D., Armstrong, D., Jackson, M.B. (eds) Calcium and Ion Channel Modulation. Springer, Boston, MA. https://doi.org/10.1007/978-1-4613-0975-8_14
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DOI: https://doi.org/10.1007/978-1-4613-0975-8_14
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