title: Independent release of supranormal acetylcholine quanta at the rat neuromuscular junction.
abstract: This electrophysiological study deals with the occurrence and with the mode of release of unusually large miniature end-plate potentials at the rat neuromuscular junction during physiological conditions. A specific limit for the normal miniature end-plate potential amplitude at each cell studied was determined after fitting the observed frequency-amplitude histogram to a Gaussian distribution. The relative abundance of giant miniature end-plate potentials was 4.15% at room temperature. The occurrence of giant miniature end-plate potentials was temperature dependent. The percentage of giant miniature end-plate potentials was 5.8% and 0.61% at 35 degrees C and at 16 degrees C, respectively. The amplitude-independence of the intervals between miniature end-plate potentials was demonstrated at room temperature as well as at 35 degrees C and at 16 degrees C. The results of this study show that giant miniature end-plate potentials are produced by acetylcholine packets which are released independently and that they are not a consequence of the synchronous release of several normal-sized quanta. Moreover, the results indicate that during physiological conditions a minor but regular proportion of the spontaneous release of acetylcholine is made up of larger packets, which produce miniature end-plate potentials of supranormal amplitude.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009045:Motor Endplate / Q000502:physiology; D009469:Neuromuscular Junction / Q000502:physiology*; D051381:Rats; D009435:Synaptic Transmission; D013572:Synaptic Vesicles / Q000502:physiology; D013696:Temperature
chemical_list: D000109:Acetylcholine