The contribution of mitochondrial calcium uptake to phasic and asynchronous release at the lizard motor nerve synapse and the effect of varying external calcium

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Physiology and Biophysics

First Committee Member

Ellen F. Barrett - Committee Chair


I investigated how inhibition of mitochondrial Ca 2+ uptake affects stimulation-induced increases in cytosolic [Ca 2+], and phasic and asynchronous transmitter release, in lizard motor terminals in 2 and 0.5 mM bath [Ca2+]. Lowering bath [Ca 2+] reduced the rate of rise, but not the final amplitude, of the increase in mitochondrial [Ca2+] during 50 Hz stimulation. The amplitude of the stimulation-induced increase in cytosolic [Ca 2+] was reduced in low bath [Ca2+], and increased when mitochondrial Ca2+ uptake was inhibited by depolarizing mitochondria. In 2 mM Ca2+ end-plate potentials (epps) depressed by 53% following 10 s of 50 Hz stimulation, and this depression increased to 80% following mitochondrial depolarization. In contrast, in 0.5 mM Ca2+ the same stimulation pattern increased epps by about 3.4-fold, and this increase was even greater (transiently) following mitochondrial depolarization. In both 2 and 0.5 mM [Ca2+] mitochondrial depolarization increased asynchronous release during the 50 Hz train, and increased the total vesicular release (phasic and asynchronous) measured by destaining of the styryl dye FM2-10. These results suggest that, by limiting the stimulation-induced increase in cytosolic [Ca2+], mitochondrial Ca2+ uptake maintains a high ratio of phasic to asynchronous release, thus helping to sustain neuromuscular transmission during repetitive stimulation. Interestingly, the quantal content of the epp reached during 50 Hz stimulation stabilized at a similar level (∼20 quanta) in both 2 and 0.5 mM Ca2+. A similar convergence was measured in oligomycin, which inhibits mitochondrial ATP synthesis without depolarizing mitochondria, but quantal contents fell below 20 when mitochondria were depolarized in 2 mM Ca2+.


Biology, Neuroscience

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