Intracellular movements of fluorescently labeled synaptic vesicles in frog motor nerve terminals during nerve stimulation.
We stained synaptic vesicles in frog motor nerve terminals with FM1-43 and studied changes in the shape and position of vesicle clusters during nerve stimulation. Each stained vesicle cluster appeared as a fluorescent spot. During repetitive nerve stimulation the spots gradually dimmed, most without changing shape or position. Occasionally, however, a spot moved, appearing in some cases to stream toward and coalesce with a neighboring spot. This suggests the existence of translocation mechanisms that can actively move vesicles in a coordinated fashion between vesicle clusters. Within single clusters, we saw no signs of such directed vesicle movements. Fluorescent spots in terminals viewed from the side with a confocal microscope did not shrink toward the presynaptic membrane during nerve stimulation, but dimmed uniformly. This suggests that vesicles continuously mix within a cluster during destaining and provides no evidence of active vesicle translocators within single vesicle clusters for moving vesicles to the presynaptic membrane.
Betz
W J
WJ
Department of Physiology, University of Colorado School of Medicine, Denver 80262.
Bewick
G S
GS
Ridge
R M
RM
D000818:Animals; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D008856:Microscopy, Fluorescence; D009046:Motor Neurons / Q000502:physiology*; D009068:Movement; D009411:Nerve Endings / Q000502:physiology*; D011894:Rana pipiens; D013572:Synaptic Vesicles / Q000502:physiology*
D005456:Fluorescent Dyes