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A possible role of the junctional face protein JP‐45 in modulating Ca 2+ release in skeletal muscle
Author(s) -
Gouadon E.,
Schuhmeier R. P.,
Ursu D.,
Anderson A. A.,
Treves S.,
Zorzato F.,
LehmannHorn F.,
Melzer W.
Publication year - 2006
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.2005.104406
Subject(s) - skeletal muscle , biophysics , depolarization , chemistry , myogenesis , calsequestrin , myocyte , endoplasmic reticulum , membrane potential , voltage clamp , patch clamp , c2c12 , ryanodine receptor , microbiology and biotechnology , biochemistry , in vitro , biology , endocrinology , receptor
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).