Extrusion of Ca2+ from mouse motor terminal mitochondria via a Na+–Ca2+ exchanger increases post-tetanic evoked release

• Published in: The Journal of physiology 2006-08, Vol.574 (3), p.663-675
• Main Authors: García-Chacón, Luis E, Nguyen, Khanh T, David, Gavriel, Barrett, Ellen F
• Format: Article
• Language: English
• Subjects: Action Potentials - physiology; Animals; Calcium - metabolism; Calcium Signaling - physiology; Cells, Cultured; Electric Stimulation; Mice; Mice, Inbred C57BL; Mitochondria - physiology; Motor Neurons - physiology; Muscle Contraction - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Neuroscience; Presynaptic Terminals - metabolism; Sodium-Calcium Exchanger - metabolism
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2006.110841

Mitochondria sequester much of the Ca 2+ that enters motor nerve terminals during repetitive stimulation at frequencies exceeding 10–20 Hz. We studied the post-stimulation extrusion of Ca 2+ from mitochondria by measuring changes in matrix [Ca 2+ ] with fluorescent indicators loaded into motor terminal mitochondria in the mouse levator auris longus muscle. Trains of action potentials at 50 Hz produced a rapid increase in mitochondrial [Ca 2+ ] followed by a plateau, which was usually maintained after the end of the stimulus train and then slowly decayed back to baseline. Increasing the Ca 2+ load delivered to the terminal by increasing the number of stimuli (from 500 to 2000) or the stimulation frequency (from 50 to 100 Hz), by increasing bath [Ca 2+ ], or by prolonging the action potential with 3,4-diaminopyridine (100 μ m ) prolonged the post-stimulation decay of mitochondrial [Ca 2+ ] without increasing the amplitude of the plateau during stimulation. Inhibiting the opening of the mitochondrial permeability transition pore with cyclosporin A (5 μ m ) had no significant effect on the decay of mitochondrial [Ca 2+ ]. Inhibition of the mitochondrial Na + –Ca 2+ exchanger with CGP-37157 (50 μ m ) dramatically prolonged the post-stimulation decay of mitochondrial [Ca 2+ ], reduced post-stimulation residual cytosolic [Ca 2+ ], and reduced the amplitude of endplate potentials evoked after the end of a stimulus train in the presence of both low and normal bath [Ca 2+ ]. These findings suggest that Ca 2+ extrusion from motor terminal mitochondria occurs primarily via the mitochondrial Na + –Ca 2+ exchanger and helps to sustain post-tetanic transmitter release at mouse neuromuscular junctions.