Presynaptic function is altered in snake K+-depolarized motor nerve terminals containing compromised mitochondria.
Presynaptic function was investigated at K+-stimulated motor nerve terminals in snake costocutaneous nerve muscle preparations exposed to carbonyl cyanide m-chlorophenylhydrazone (CCCP, 2 M), oligomycin (8 g x 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 mM), 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 ([Ca2+]i). For oligomycin-treated nerve terminals, a progressive elevation of [Ca2+]i could occur as the cytoplasmic ATP/ADP ratio decreases, causing energy-dependent Ca2+ 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 Ca2+ buffering and ATP production were both inhibited. Therefore, the proposed sustained elevation of [Ca2+]i could occur more rapidly.
Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, VT 05405, USA.
M A
MA
Calupca
C
C
Prior
L A
LA
Merriam
G M
GM
Hendricks
R L
RL
Parsons
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D017812:Colubridae / Q000502:physiology*; D004705:Endocytosis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D009045:Motor Endplate / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000294:innervation*; D009840:Oligomycins / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D011422:Propionates / Q000494:pharmacology; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D013572:Synaptic Vesicles / Q000502:physiology; D014475:Uncoupling Agents / Q000494:pharmacology
D004791:Enzyme Inhibitors; C073804:FM1 43; D005456:Fluorescent Dyes; D009840:Oligomycins; D011422:Propionates; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D014475:Uncoupling Agents; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; D005947:Glucose; C029658:propionic acid; D011188:Potassium; D002118:Calcium