Abstract
The mechanisms that terminate Ca 2+ release from the sarcoplasmic reticulum are not fully understood. D4cpv-Casq1 (Sztretye et al. 2011. J. Gen. Physiol. doi:10.1085/jgp.201010591) was used in mouse skeletal muscle cells under voltage clamp to measure free Ca 2+ concentration inside the sarcoplasmic reticulum (SR), [Ca 2+] SR, simultaneously with that in the cytosol, [Ca 2+] c, during the response to long-lasting depolarization of the plasma membrane. The ratio of Ca 2+ release flux (derived from [Ca 2+] c(t)) over the gradient that drives it (essentially equal to [Ca 2+] SR) provided directly, for the first time, a dynamic measure of the permeability to Ca 2+ of the releasing SR membrane. During maximal depolarization, flux rapidly rises to a peak and then decays. Before 0.5 s, [Ca 2+] SR stabilized at ~35% of its resting level; depletion was therefore incomplete. By 0.4 s of depolarization, the measured permeability decayed to ~10% of maximum, indicating ryanodine receptor channel closure. Inactivation of the t tubule voltage sensor was immeasurably small by this time and thus not a significant factor in channel closure. In cells of mice null for Casq1, permeability did not decrease in the same way, indicating that calsequestrin (Casq) is essential in the mechanism of channel closure and termination of Ca 2+ release. The absence of this mechanism explains why the total amount of calcium releasable by depolarization is not greatly reduced in Casq-null muscle (Royer et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.201010454). When the fast buffer BAPTA was introduced in the cytosol, release flux became more intense, and the SR emptied earlier. The consequent reduction in permeability accelerated as well, reaching comparable decay at earlier times but comparable levels of depletion. This observation indicates that [Ca 2+] SR, sensed by Casq and transmitted to the channels presumably via connecting proteins, is determinant to cause the closure that terminates Ca 2+ release.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 231-247 |
| Number of pages | 17 |
| Journal | Journal of General Physiology |
| Volume | 138 |
| Issue number | 2 |
| DOIs | |
| State | Published - Aug 2011 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Physiology
Cite this
Measurement of RyR permeability reveals a role of calsequestrin in termination of SR Ca 2+ release in skeletal muscle. / Sztretye, Monika; Yi, Jianxun; Figueroa, Lourdes; Zhou, Jingsong; Royer, Leandro; Allen, Paul; Brum, Gustavo; Ríos, Eduardo.
In: Journal of General Physiology, Vol. 138, No. 2, 08.2011, p. 231-247.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Measurement of RyR permeability reveals a role of calsequestrin in termination of SR Ca 2+ release in skeletal muscle
AU - Sztretye, Monika
AU - Yi, Jianxun
AU - Figueroa, Lourdes
AU - Zhou, Jingsong
AU - Royer, Leandro
AU - Allen, Paul
AU - Brum, Gustavo
AU - Ríos, Eduardo
PY - 2011/8
Y1 - 2011/8
N2 - The mechanisms that terminate Ca 2+ release from the sarcoplasmic reticulum are not fully understood. D4cpv-Casq1 (Sztretye et al. 2011. J. Gen. Physiol. doi:10.1085/jgp.201010591) was used in mouse skeletal muscle cells under voltage clamp to measure free Ca 2+ concentration inside the sarcoplasmic reticulum (SR), [Ca 2+] SR, simultaneously with that in the cytosol, [Ca 2+] c, during the response to long-lasting depolarization of the plasma membrane. The ratio of Ca 2+ release flux (derived from [Ca 2+] c(t)) over the gradient that drives it (essentially equal to [Ca 2+] SR) provided directly, for the first time, a dynamic measure of the permeability to Ca 2+ of the releasing SR membrane. During maximal depolarization, flux rapidly rises to a peak and then decays. Before 0.5 s, [Ca 2+] SR stabilized at ~35% of its resting level; depletion was therefore incomplete. By 0.4 s of depolarization, the measured permeability decayed to ~10% of maximum, indicating ryanodine receptor channel closure. Inactivation of the t tubule voltage sensor was immeasurably small by this time and thus not a significant factor in channel closure. In cells of mice null for Casq1, permeability did not decrease in the same way, indicating that calsequestrin (Casq) is essential in the mechanism of channel closure and termination of Ca 2+ release. The absence of this mechanism explains why the total amount of calcium releasable by depolarization is not greatly reduced in Casq-null muscle (Royer et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.201010454). When the fast buffer BAPTA was introduced in the cytosol, release flux became more intense, and the SR emptied earlier. The consequent reduction in permeability accelerated as well, reaching comparable decay at earlier times but comparable levels of depletion. This observation indicates that [Ca 2+] SR, sensed by Casq and transmitted to the channels presumably via connecting proteins, is determinant to cause the closure that terminates Ca 2+ release.
AB - The mechanisms that terminate Ca 2+ release from the sarcoplasmic reticulum are not fully understood. D4cpv-Casq1 (Sztretye et al. 2011. J. Gen. Physiol. doi:10.1085/jgp.201010591) was used in mouse skeletal muscle cells under voltage clamp to measure free Ca 2+ concentration inside the sarcoplasmic reticulum (SR), [Ca 2+] SR, simultaneously with that in the cytosol, [Ca 2+] c, during the response to long-lasting depolarization of the plasma membrane. The ratio of Ca 2+ release flux (derived from [Ca 2+] c(t)) over the gradient that drives it (essentially equal to [Ca 2+] SR) provided directly, for the first time, a dynamic measure of the permeability to Ca 2+ of the releasing SR membrane. During maximal depolarization, flux rapidly rises to a peak and then decays. Before 0.5 s, [Ca 2+] SR stabilized at ~35% of its resting level; depletion was therefore incomplete. By 0.4 s of depolarization, the measured permeability decayed to ~10% of maximum, indicating ryanodine receptor channel closure. Inactivation of the t tubule voltage sensor was immeasurably small by this time and thus not a significant factor in channel closure. In cells of mice null for Casq1, permeability did not decrease in the same way, indicating that calsequestrin (Casq) is essential in the mechanism of channel closure and termination of Ca 2+ release. The absence of this mechanism explains why the total amount of calcium releasable by depolarization is not greatly reduced in Casq-null muscle (Royer et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.201010454). When the fast buffer BAPTA was introduced in the cytosol, release flux became more intense, and the SR emptied earlier. The consequent reduction in permeability accelerated as well, reaching comparable decay at earlier times but comparable levels of depletion. This observation indicates that [Ca 2+] SR, sensed by Casq and transmitted to the channels presumably via connecting proteins, is determinant to cause the closure that terminates Ca 2+ release.
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U2 - 10.1085/jgp.201010592
DO - 10.1085/jgp.201010592
M3 - Article
C2 - 21788611
AN - SCOPUS:79961112228
VL - 138
SP - 231
EP - 247
JO - Journal of General Physiology
JF - Journal of General Physiology
SN - 0022-1295
IS - 2
ER -