Facilitation and delayed release at single frog neuromuscular junctions.
Facilitation and delayed spontaneous release were recorded from neuromuscular junctions at 2 temperatures. In some experiments, Sr2+ substituted for Ca2+. We measured the ratio of delayed release to resting spontaneous release (D), and the ratio of the second end-plate potential amplitude to the first (F). An extension of the model of Barton et al. (1983) relating Ca2+ to evoked and spontaneous release is presented. If residual Ca2+ accounts for facilitation and delayed release, then D must be greater than F. In all of our experiments, D was greater than F. We conclude that residual Ca2+ is sufficient to account for facilitation and delayed release at the frog neuromuscular junction. However, D falls abruptly at a time when F is almost unaltered, which raises serious difficulties in accepting the residual calcium hypothesis.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D008433:Mathematics; D008959:Models, Neurological; D009469:Neuromuscular Junction / Q000502:physiology*; D011894:Rana pipiens; D013324:Strontium / Q000378:metabolism; D013696:Temperature
D002118:Calcium; D013324:Strontium