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Effect of dissociating cytosolic calcium and metabolic rate on intracellular P O2 kinetics in single frog myocytes
Author(s) -
Kindig Casey A.,
Stary Creed M.,
Hogan Michael C.
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.074922
Subject(s) - chemistry , kinetics , calcium , isometric exercise , myocyte , cytosol , biophysics , contraction (grammar) , intracellular , medicine , ryanodine receptor , endocrinology , biochemistry , biology , enzyme , physics , organic chemistry , quantum mechanics
The purpose of this investigation was to utilize 2,3‐butanedione monoxime (BDM; an inhibitor of contractile activation) to dissociate cytosolic [Ca 2+ ] ([Ca 2+ ] c ) from the putative respiratory regulators that arise from muscle contraction‐induced ATP utilization in order to determine the relative contribution of [Ca 2+ ] c on intracellular P O2 ( P iO2 ) kinetics during the transition from rest to contractions in single skeletal myocytes isolated from Xenopus laevis lumbrical muscle. Myocytes were subjected to electrically induced isometric tetanic contractions (0.25 Hz; 2‐min bouts) while peak tension and either [Ca 2+ ] c ( n = 7; ratiometric fluorescence microscopy) or P iO2 ( n = 7; phosphorescence microscopy) was measured continuously. Cells were studied under both control and 3 m m BDM conditions in randomized order. Initial (control, 100 ± 0%; BDM, 72.6 ± 4.6%), midpoint (control, 86.7 ± 1.8%; BDM, 61.6 ± 4.1%) and end (control, 85.0 ± 2.8%; BDM, 57.5 ± 5.0%) peak tensions (normalized to initial control values) were significantly reduced ( P < 0.05) with BDM compared with control ( n = 14). Despite the reduced peak tension, peak [Ca 2+ ] c was not altered ( P > 0.05) between control and BDM trials. Thus, the peak tension‐to‐peak [Ca 2+ ] c ratio was reduced with BDM compared with control. The absolute fall in P iO2 with contractions, which is proportional to the rise in , was significantly reduced with BDM (13.2 ± 1.3 mmHg) compared with control (22.0 ± 2.0 mmHg). However, P iO2 onset kinetics (i.e. mean response time (MRT)) was not altered between BDM (66.8 ± 8.0 s) and control (64.9 ± 6.3 s) trials. Therefore, the initial rate of change (defined as the fall in P iO2 /MRT) was significantly slower in BDM fibres compared with control. These data demonstrate in these isolated single skeletal muscle fibres that unchanged peak [Ca 2+ ] c in the face of reduced metabolic feedback from the contractile sites evoked with BDM did not alter P iO2 onset kinetics in isolated single frog myocytes, suggesting that metabolic signals arising from the contractile sites play a more substantial role than [Ca 2+ ] c in the signalling pathway to oxidative phosphorylation during the transition from rest to repeated tetanic contractions.