A possible role of the junctional face protein JP-45 in modulating Ca2+ release in skeletal muscle

We investigated the functional role of JP-45, a recently discovered protein of the junctional face membrane (JFM) of skeletal muscle. For this purpose, we expressed JP-45 C-terminally tagged with the fluorescent protein DsRed2 by nuclear microinjection in myotubes derived from the C2C12 skeletal mus...

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Bibliographic Details
Published in:The Journal of physiology 2006-04, Vol.572 (1), p.269-280
Main Authors: Gouadon, E, Schuhmeier, R P, Ursu, D, Anderson, A A, Treves, S, Zorzato, F, Lehmann-Horn, F, Melzer, W
Format: Article
Language:English
Subjects:
Animals
Calcium - metabolism
Calcium Signaling - physiology
Cell Line
Humans
Ion Channel Gating - physiology
Membrane Potentials - physiology
Membrane Proteins - metabolism
Mice
Muscle Fibers, Skeletal - physiology
Muscle, Skeletal - physiology
Ryanodine Receptor Calcium Release Channel - physiology
Sarcoplasmic Reticulum - physiology
Skeletal Muscle and Exercise
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Summary:We investigated the functional role of JP-45, a recently discovered protein of the junctional face membrane (JFM) of skeletal muscle. For this purpose, we expressed JP-45 C-terminally tagged with the fluorescent protein DsRed2 by nuclear microinjection in myotubes derived from the C2C12 skeletal muscle cell line and performed whole-cell voltage-clamp experiments. We recorded in parallel cell membrane currents and Ca 2+ signals using fura-2 during step depolarization. It was found that properties of the voltage-activated Ca 2+ current were not significantly changed in JP-45–DsRed2-expressing C2C12 myotubes whereas the amplitude of depolarization-induced Ca 2+ transient was decreased compared to control myotubes expressing only DsRed2. Converting Ca 2+ transients to Ca 2+ input flux using a model fit approach to quantify Ca 2+ removal, the change could be attributed to an alteration in voltage-activated Ca 2+ permeability rather than to altered removal properties or a lower Ca 2+ content of the sarcoplasmic reticulum (SR). Determining non-linear capacitive currents revealed a reduction of Ca 2+ permeability per voltage-sensor charge. The results may be explained by a modulatory effect of JP-45 related to its reported in vitro interaction with the dihydropyridine receptor and the SR Ca 2+ binding protein calsequestrin (CSQ).
ISSN:0022-3751
1469-7793
DOI:10.1113/jphysiol.2005.104406