Spontaneous tension oscillation in skinned bovine cardiac muscle |
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Authors: | Norio Fukuda Hideaki Fujita Takashi Fujita Shin’ichi Ishiwata |
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Institution: | (1) Department of Physics, School of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169 Japan, JP;(2) Advanced Research Institute for Science and Engineering , Waseda University, 3-4-1 Okubo, Shinjuku-ku, Toyko 169, Japan, JP;(3) Pharmacology and Molecular Biology Research Laboratories, Sankyo Co., Ltd., 1-2-58 Hiromachi, Shinagawa-ku, Tokyo 140, Japan, JP |
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Abstract: | Skinned fibres from bovine ventricles exhibited spontaneous tension oscillations when MgADP and inorganic phosphate (Pi)
were added to the solution bathing fibres in the relaxed state (ADP-SPOC). A similar type of oscillation was observed at intermediate
concentrations of free Ca2+ in the absence of MgADP and Pi (Ca-SPOC). To investigate the correlation between ADP-SPOC and Ca-SPOC, we constructed two-dimensional
state diagrams of cardiac muscle using different concentrations of Pi (0–20 mM) and free Ca2+ pCa=around 5 (+Ca2+), pCa=5.15–6.9 and +EGTA (–Ca2+)], with varying concentrations of MgADP (0–10 mM), with 2 mM MgATP and 2 mM free Mg2+ maintaining ionic strength at 0.15±0.01 M, pH 7.0, 25 °C. The three-dimensional (pCa-Pi-MgADP) state diagram thus obtained
was divided into three regions, i.e. the contraction region in which tension oscillation was undetectable, the spontaneous
tension oscillation (SPOC) region and the relaxation region. We found that the regions of ADP-SPOC and Ca-SPOC were continuously
connected by a single oscillation region sandwiched between the contraction and relaxation regions. The state diagram, which
encompasses physiological conditions, shows that the probability of SPOC is higher in cardiac muscle than in skeletal muscle.
From these results, we suggest that, despite distinct ionic conditions, the molecular state of cross-bridges during SPOC is
common to both ADP-SPOC and Ca-SPOC.
Received 19 February 1996 / Received after revision: 16 July 1996 / Accepted: 14 August 1996 |
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Keywords: | Cardiac muscle Oscillation Spontaneous oscillatory contraction Spontaneous tension oscillation State diagram of muscle |
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