A possible role of the junctional face protein JP-45 in modulating Ca super(2+) release in skeletal muscle

• 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
• ISSN: 0022-3751; 1469-7793

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 super(2+) signals using fura-2 during step depolarization. It was found that properties of the voltage-activated Ca super(2+) current were not significantly changed in JP-45-DsRed2-expressing C2C12 myotubes whereas the amplitude of depolarization-induced Ca super(2+) transient was decreased compared to control myotubes expressing only DsRed2. Converting Ca super(2+) transients to Ca super(2+) input flux using a model fit approach to quantify Ca super(2+) removal, the change could be attributed to an alteration in voltage-activated Ca super(2+) permeability rather than to altered removal properties or a lower Ca super(2+) content of the sarcoplasmic reticulum (SR). Determining non-linear capacitive currents revealed a reduction of Ca super(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 super(2+) binding protein calsequestrin (CSQ).