Voltage- and ligand-gated ryanodine receptors are functionally separated in developing C2C12 mouse myotubes

Authors

  • Paola Lorenzon,

    Corresponding author
    1. Department of Physiology and Pathology and Centre for Neuroscience B.R.A.I.N., University of Trieste, Trieste, Italy
    • Corresponding author
      P. Lorenzon: Department of Physiology and Pathology, University of Trieste, Via A. Fleming 22, I-34127 Trieste, Italy. Email: pielle@fc.univ.trieste.it

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  • Fabio Grohovaz,

    1. C.N.R. Cellular and Molecular Pharmacology Centre and B. Ceccarelli Centre, Dibit, S. Raffaele Scientific Institute, Milan, Italy
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  • Fabio Ruzzier

    1. Department of Physiology and Pathology and Centre for Neuroscience B.R.A.I.N., University of Trieste, Trieste, Italy
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Abstract

  • 1In order to further understand the role of voltage- and ligand-gated ryanodine receptors in the control of intracellular Ca2+ signalling during myogenesis, changes in cytosolic free calcium concentration ([Ca2+]i) were investigated by fura-2 videoimaging in C2C12 mouse myotubes developing in vitro.
  • 2A synchronous [Ca2+]i increase was observed after depolarisation with high [K+], while the Ca2+ response propagated as a wave following caffeine administration. Application of the two stimuli to the same myotube often revealed the existence of cellular zones that were responsive to depolarisation but not to caffeine.
  • 3Focal application of high [K+] promoted a [Ca2+]i response detectable only in the cellular areas close to the pipette tip, while focal application of caffeine elicited a [Ca2+]i increase which spread as a Ca2+ wave. Buffering of [Ca2+]i by BAPTA did not affect the pattern of the depolarisation-induced [Ca2+]i transient but abolished the Ca2+ waves elicited by caffeine.
  • 4When high [K+] and caffeine were applied in sequence, reciprocal inhibition of the [Ca2+]i responses was observed.
  • 5Our results suggest that the different spatial patterns of [Ca2+]i responses are due to uneven distribution of voltage- and ligand-gated ryanodine receptors within the myotube. These two types of receptor control two functionally distinct Ca2+ pools which are part of a common intracellular compartment. Finally, the two differently operated ryanodine receptor channels appear to be independently activated, so that a mechanism of Ca2+-induced Ca2+ release is not required to sustain the global response in C2C12 myotubes.

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