Abstract
Miniature endplate potentials and currents were recorded from frog sartorius muscle fibres. As expected from previous work, La 3+ caused a very large increase in miniature endplate potential frequency, followed by a progressive decrease, ending in the virtually complete disappearance of miniature endplate potentials. Soon after its application, La 3+ caused an increase in the amplitude of miniature endplate potentials due to a lengthening of the underlying miniature endplate currents. Analysis of membrane current fluctuations produced by acetylcholine showed that La 3+ caused an increase in the lifetime of the channels opened by acetylcholine. After miniature endplate potentials had vanished following La 3+ treatment, the muscles were placed in organ culture conditions to see if miniature endplate potentials would reappear. After several hours miniature endplate potential activity was resumed in about 25% of the endplates, and disappeared again a few hours later, presumably because of accelerated nerve terminal degeneration. Preliminary electron microscopic observations suggest that the recovery of miniature endplate potential activity was accompanied by re-formation of synaptic vesicles in the motor endings.
Published Version
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