Target Cell Contact Modulates Spontaneous Quantal and Non-Quantal Acetylcholine Release by Xenopus Spinal Neurons
Xenopus nerve-muscle cell culture has proved to be an excellent preparation for study of the development of neuronal ion channel and membrane properties (Spitzer, 1976; Spitzer and Lamborghini, 1976; Willard, 1980) and for studies of synaptogenesis. Much is already known about the properties of the synapses formed in culture, and the changes that take place during maturation, particularly post-synaptically. At synapses formed by growing neurites on muscle cells in 1–2 day old cultures, there are quantal miniature endplate potentials (mEPPs) at frequencies ranging from 0.5 — 4 Hz, with skewed amplitude histograms (Kidokoro et al., 1980; Chow and Poo, 1985). It appears that, at the time of initial synaptic contact, there is no postsynaptic specialization at the site of release—the responses are mediated simply by the acetylcholine (ACh) receptors spread diffusely over the muscle cell’s surface. Only after a time course of hours to days, does the sub-synaptic site develop a high concentration of ACh receptors and other specializations (Anderson and Cohen, 1977; Anderson et al., 1977; Weldon and Cohen, 1979; Kidokoro et al., 1980; Cohen and Weldon, 1980; Takahashi et al., 1987; Chow et al., 1987).
KeywordsCholine Hepes Acetylcholine Acetyl Alan
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