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Updated: Jun 4, 2026
Measuring Neuromuscular Junction Functionality
Published on: August 6, 2017
Repetitive nerve stimulation transiently opens the mitochondrial permeability transition pore in motor nerve
Khanh T Nguyen1, John N Barrett, Luis García-Chacón
1Department of Physiology and Biophysics, University of Miami Miller School of Medicine, PO Box 016430, Miami, FL 33101, USA.
Abstract:
Mitochondria in motor nerve terminals temporarily sequester large Ca(2+) loads during repetitive stimulation. In wild-type mice this Ca(2+) uptake produces a small (<5 mV), transient depolarization of the mitochondrial membrane potential (Ψ(m), motor nerve stimulated at 100 Hz for 5s). We demonstrate that this stimulation-induced Ψ(m) depolarization attains much higher amplitudes in motor terminals of symptomatic mice expressing the G93A or G85R mutation of human superoxide dismutase 1 (SOD1), models of familial amyotrophic lateral sclerosis (fALS). These large Ψ(m) depolarizations decayed slowly and incremented with successive stimulus trains. Additional Ψ(m) depolarizations occurred that were not synchronized with stimulation. These large Ψ(m) depolarizations were reduced (a) by cyclosporin A (CsA, 1-2 microM), which inhibits opening of the mitochondrial permeability transition pore (mPTP), or (b) by replacing bath Ca(2+) with Sr(2+), which enters motor terminals and mitochondria but does not support mPTP opening. These results are consistent with the hypothesis that the large Ψ(m) depolarizations evoked by repetitive stimulation in motor terminals of symptomatic fALS mice result from mitochondrial dysfunction that increases the likelihood of transient mPTP opening during Ca(2+) influx. Such mPTP openings, a sign of mitochondrial stress, would disrupt motor terminal handling of Ca(2+) loads and might thereby contribute to motor terminal degeneration in fALS mice. Ψ(m) depolarizations resembling those in symptomatic fALS mice could be elicited in wild-type mice following a 0.5-1h exposure to diamide (200 microM), which produces an oxidative stress, but these depolarizations were not reduced by CsA.
Insights
Mitochondrial dysfunction in familial ALS models causes significant membrane potential depolarization during nerve stimulation. This dysfunction, linked to mitochondrial permeability transition pore opening, may contribute to motor neuron degeneration.
Area of Science:
- Neuroscience
- Mitochondrial Biology
- Neurodegenerative Diseases
Background:
- Mitochondria in motor nerve terminals buffer calcium (Ca2+) during stimulation, causing minor membrane potential (Ψ(m)) depolarization in healthy mice.
- Familial amyotrophic lateral sclerosis (fALS) involves mutations in superoxide dismutase 1 (SOD1), leading to motor neuron degeneration.
- Mitochondrial dysfunction is implicated in neurodegenerative processes.
Purpose of the Study:
- To investigate mitochondrial membrane potential (Ψ(m)) dynamics in motor nerve terminals of fALS mouse models during repetitive stimulation.
- To explore the mechanisms underlying abnormal Ψ(m) depolarization in fALS motor terminals.
- To assess the role of mitochondrial permeability transition pore (mPTP) opening in fALS-associated mitochondrial dysfunction.
Main Methods:
- Measured mitochondrial membrane potential (Ψ(m)) in motor nerve terminals of wild-type and symptomatic G93A/G85R SOD1 mutant mice.
- Utilized repetitive nerve stimulation protocols (100 Hz for 5s).
- Administered cyclosporin A (CsA) to inhibit mPTP opening and used Sr2+ instead of Ca2+ to investigate the role of mPTP in Ψ(m) changes.
Main Results:
- Symptomatic fALS mice exhibited significantly larger and slower decaying Ψ(m) depolarizations compared to wild-type mice.
- These depolarizations incremented with successive stimulation trains and occurred spontaneously.
- Cyclosporin A and Sr2+ substitution reduced the large Ψ(m) depolarizations in fALS mice, implicating mPTP opening.
Conclusions:
- Repetitive stimulation induces substantial mitochondrial dysfunction in fALS motor terminals, characterized by increased mPTP opening.
- This dysfunction disrupts mitochondrial calcium handling and may contribute to motor terminal degeneration in fALS.
- Oxidative stress can mimic some aspects of fALS-induced Ψ(m) changes, but the CsA sensitivity differs.
