NDLI: Voltage-Activated Calcium Signals in Myotubes Loaded with High Concentrations of EGTA

Content Provider	PubMed Central
Author	Schuhmeier, R. P. Dietze, B. Ursu, D. Lehmann-horn, F. Melzer, W.
Copyright Year	2003
Abstract	In the present study we describe the analysis of optically recorded whole cell Ca2+ transients elicited by depolarization in cultured skeletal myotubes. Myotubes were obtained from the mouse muscle-derived cell line C2C12 and from mouse satellite cells. The cells were voltage-clamped and perfused with an artificial intracellular solution containing 15 mM EGTA to ensure that the bulk of the Ca2+ mobilized by depolarization is bound to this extrinsic buffer. The apparent on- and off-rate constants of EGTA and the dissociation rate constant of fura-2 in the cell were estimated by investigating the Ca2+-dependence of kinetic components of the fluorescence decay after repolarization. These parameters were used to calculate the time course of the total voltage-controlled flux of Ca2+ to the myoplasmic space (Ca2+ input flux). The validity of the procedure was confirmed by model simulations using artificial Ca2+ input fluxes. Both C2C12 and primary-cultured myotubes showed a very similar phasic-tonic time course of the Ca2+ input flux. In most measurements, the input flux was considerably larger and showed a different time course than the estimated Ca2+ flux carried by the L-type Ca2+ channels, indicating that it consists mainly of voltage-controlled Ca2+ release from the sarcoplasmic reticulum. In cells with extremely small fluorescence transients, the calculated input fluxes matched the kinetic characteristics of the Ca2+ inward current, indicating that Ca2+ release was absent. These measurements served as a control for the fidelity of the fluorimetric flux analysis. The procedures promise a deeper insight into alterations of Ca2+ release gating in studies employing myotube expression systems for mutant or chimeric protein components of excitation-contraction coupling.
Related Links	http://dx.doi.org/10.1016/s0006-3495(03)74923-6
Ending Page	1078
Page Count	14
Starting Page	1065
File Format	PDF
ISSN	00063495
e-ISSN	15420086
Journal	Biophysical Journal
Issue Number	2
Volume Number	84
Language	English
Publisher	Biophysical Society
Publisher Date	2003-02-01
Access Restriction	Open
Rights Holder	Biophysical Society
Subject Keyword	Biophysics Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biophysics

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