Cytoplasmic Free Concentrations of Ca^<2+> and Mg^<2+> in Skeletal Muscle Fibers at Rest and during Contraction

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Abstract

This review summarizes estimates for cytoplasmic-free concentrations of Ca<SUP>2+</SUP> ([Ca<SUP>2+</SUP>]<SUB>i</SUB>) and Mg<SUP>2+</SUP> ([Mg<SUP>2+</SUP>]<SUB>i</SUB>) at rest and during contraction of skeletal muscles, from which substantial quantitative information about them has been accumulated. Although the estimates of resting [Ca<SUP>2+</SUP>]<SUB>i</SUB> in the literature widely differ, which is because of the variety of difficulties related to different methodologies used, recent studies suggest that estimates of resting [Ca<SUP>2+</SUP>]<SUB>i</SUB> of approximately 0.05-0.1 μM are likely to be correct. Following action potential propagation, the Ca<SUP>2+</SUP> release from the sarcoplasmic reticulum causes a transient rise of [Ca<SUP>2+</SUP>]<SUB>i</SUB> (Ca<SUP>2+</SUP> transient). The large peak amplitude and brief time course of the Ca<SUP>2+</SUP> transients have been established only recently by studies with low-affinity Ca<SUP>2+</SUP> indicators developed in the past decade. These technical improvements in [Ca<SUP>2+</SUP>]<SUB>i</SUB> measurements have made it possible to study relationships between [Ca<SUP>2+</SUP>]<SUB>i</SUB> and force in intact muscle fibers. in the second part of this review, various estimates of [Mg<SUP>2+</SUP>]<SUB>i</SUB> in the resting muscle are discussed. Relatively recent estimates of the [Mg<SUP>2+</SUP>]<SUB>i</SUB> level appear to be about 1.0 mM. Using the current knowledge of concentrations and reaction properties of intracellular Ca<SUP>2+</SUP> -Mg<SUP>2+</SUP> binding sites, we constructed a model for dynamic Mg<SUP>2+</SUP> movement following Ca<SUP>2+</SUP> transients. The model predicts that with a train of action potentials, the sustained rise of [Ca<SUP>2+</SUP>]<SUB>i</SUB> produces an elevation of [Mg<SUP>2+</SUP>]<SUB>i</SUB> of about 220 μM.

Journal

  • The Japanese Journal of Physiology

    The Japanese Journal of Physiology 48(6), 421-438, 1998-12-01

    THE PHYSIOLOGICAL SOCIETY OF JAPAN

References:  114

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Cited by:  2

Codes

  • NII Article ID (NAID)
    10008305701
  • NII NACSIS-CAT ID (NCID)
    AA00691224
  • Text Lang
    ENG
  • Article Type
    Journal Article
  • ISSN
    0021521X
  • NDL Article ID
    4652846
  • NDL Source Classification
    ZS8(科学技術--医学--解剖学・生理学・生化学)
  • NDL Call No.
    Z53-D40
  • Data Source
    CJP  CJPref  NDL  J-STAGE 
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