Stimulation-induced mitochondrial [Ca2+] elevations in mouse motor terminals: comparison of wild-type with SOD1-G93A.
Changes in mitochondrial matrix [Ca2+] evoked by trains of action potentials were studied in levator auris longus motor terminals using Ca2+-sensitive fluorescent indicator dyes (rhod-2, rhod-5F). During a 2500 impulse 50 Hz train, mitochondrial [Ca2+] in most wild-type terminals increased within 5-10 s to a plateau level that was sustained until stimulation ended. This plateau was not due to dye saturation, but rather reflects a powerful buffering system within the mitochondrial matrix. The amplitude of this plateau was similar for stimulation frequencies in the range 15-100 Hz. Plateau amplitude was sensitive to temperature, with no detectable stimulation-induced increase in fluorescence at temperatures below 17 degrees C, and increasing magnitudes as temperature was increased to near-physiological levels (38 degrees C). When stimulation ended, mitochondrial [Ca2+] decayed slowly back to prestimulation levels over a time course of hundreds of seconds. Similar measurements were also made in motor terminals of mice expressing the G93A mutation of human superoxide dismutase 1 (SOD1-G93A). In mice > 100 days old, all of whom exhibited hindlimb paralysis, some terminals continued to show wild-type mitochondrial [Ca2+] responses, but in other terminals mitochondrial [Ca2+] did not plateau, but rather continued to increase throughout most of the stimulus train. Thus mechanism(s) that limit stimulation-induced increases in mitochondrial [Ca2+] may be compromised in some SOD1-G93A terminals.
Vila
Lizette
L
Department of Physiology and Biophysics R-430, University of Miami School of Medicine, PO Box 016430, Miami, FL 33101, USA.
Barrett
Ellen F
EF
Barrett
John N
JN
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004072:Digitonin / Q000494:pharmacology; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D009469:Neuromuscular Junction / Q000502:physiology; D017729:Presynaptic Terminals / Q000502:physiology*; D020112:Rhodamine 123; D013482:Superoxide Dismutase / Q000235:genetics*
D005456:Fluorescent Dyes; D020112:Rhodamine 123; C109415:SOD1 G93A protein; D013482:Superoxide Dismutase; D004072:Digitonin; D002118:Calcium