Mechanisms of calcium sequestration during facilitation at active zones of an amphibian neuromuscular junction.
The calcium transients (Delta[Ca(2+)](i)) at active zones of amphibian (Bufo marinus) motor-nerve terminals that accompany impulses, visualized using a low-affinity calcium indicator injected into the terminal, are described and the pathways of subsequent sequestration of the residual calcium determined, allowing development of a quantitative model of the sequestering processes. Blocking the endoplasmic reticulum calcium pump with thapsigargin did not affect Delta[Ca(2+)](i) for a single impulse but increased its amplitude during short trains. Blocking the uptake of calcium by mitochondria with CCCP had little effect on Delta[Ca(2+)](i) of a single impulse but greatly increased its amplitude during short trains. This present compartmental model is compatible with our previous Monte Carlo diffusion model of Ca(2+) sequestration during facilitation [Bennett, M.R., Farnell, L., Gibson, W.G., 2004. The facilitated probability of quantal secretion within an array of calcium channels of an active zone at the amphibian neuromuscular junction. Biophys. J. 86(5), 2674-2690], with the single plasmalemma pump in that model now replaced by separate pumps for the plasmalemma and endoplasmic reticulum, as well as the introduction of a mitochondrial uniporter.
Bennett
M R
MR
The Neurobiology Laboratory, Department of Physiology, The Institute for Biomedical Research, University of Sydney, New South Wales 2006, Australia. maxb@physiol.usyd.edu.au
Farnell
L
L
Gibson
W G
WG
Dickens
P
P
D000818:Animals; D002024:Bufo marinus / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D008931:Mitochondria, Muscle / Q000378:metabolism; D008954:Models, Biological; D009469:Neuromuscular Junction / Q000378:metabolism*
D000252:Calcium-Transporting ATPases; D002118:Calcium