Presynaptic function is altered in snake K+-depolarized motor nerve terminals containing compromised mitochondria

• Published in: The Journal of physiology 2001-04, Vol.532 (1), p.217-227
• Main Authors: Calupca, Michelle A., Prior, Chris, Merriam, Laura A., Hendricks, Gregory M., Parsons, Rodney L.
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Adenosine Triphosphate - metabolism; Animals; Calcium - metabolism; Carbonyl Cyanide m-Chlorophenyl Hydrazone - pharmacology; Colubridae - physiology; Endocytosis; Enzyme Inhibitors - pharmacology; Fluorescent Dyes - metabolism; Glucose - metabolism; Mitochondria - metabolism; Motor Endplate - metabolism; Motor Endplate - physiology; Motor Endplate - ultrastructure; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - physiology; Muscle, Skeletal - cytology; Muscle, Skeletal - innervation; Oligomycins - pharmacology; Original; Patch-Clamp Techniques; Potassium - metabolism; Propionates - pharmacology; Pyridinium Compounds - metabolism; Quaternary Ammonium Compounds - metabolism; Synaptic Vesicles - physiology; Uncoupling Agents - pharmacology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.2001.0217g.x

Presynaptic function was investigated at K + -stimulated motor nerve terminals in snake costocutaneous nerve muscle preparations exposed to carbonyl cyanide m -chlorophenylhydrazone (CCCP, 2 μ m ), oligomycin (8 μg ml −1 ) or CCCP and oligomycin together. Miniature endplate currents (MEPCs) were recorded at -150 mV with two-electrode voltage clamp. With all three drug treatments, during stimulation by elevated K + (35 m m ), MEPC frequencies initially increased to values > 350 s −1 , but then declined. The decline occurred more rapidly in preparations treated with CCCP or CCCP and oligomycin together than in those treated with oligomycin alone. Staining with FM1-43 indicated that synaptic vesicle membrane endocytosis occurred at some CCCP- or oligomycin-treated nerve terminals after 120 or 180 min of K + stimulation, respectively. The addition of glucose to stimulate production of ATP by glycolysis during sustained K + stimulation attenuated the decline in MEPC frequency and increased the percentage of terminals stained by FM1-43 in preparations exposed to either CCCP or oligomycin. We propose that the decline in K + -stimulated quantal release in preparations treated with CCCP, oligomycin or CCCP and oligomycin together could result from a progressive elevation of intracellular calcium concentration ([Ca 2+ ] i ). For oligomycin-treated nerve terminals, a progressive elevation of [Ca 2+ ] i could occur as the cytoplasmic ATP/ADP ratio decreases, causing energy-dependent Ca 2+ buffering mechanisms to fail. The decline in MEPC frequency could occur more rapidly in preparations treated with CCCP or CCCP and oligomycin together because mitochondrial Ca 2+ buffering and ATP production were both inhibited. Therefore, the proposed sustained elevation of [Ca 2+ ] i could occur more rapidly.