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Updated: Aug 7, 2026

Measurement of Calcium Fluctuations Within the Sarcoplasmic Reticulum of Cultured Smooth Muscle Cells Using FRET-based Confocal Imaging
Published on: June 20, 2016
Intra- and extraluminal sarcoplasmic reticulum membrane regulatory sites for Ca2(+)-induced Ca2+ release
1Department of Anesthesiology, University of Texas Health Science Center, Houston 77030.
Abstract:
A heavy skeletal muscle sarcoplasmic reticulum (SR) fraction was actively loaded stepwise with calcium until Ca2(+)-induced Ca2+ release occurred. The total Ca2+ load, T1, at which release occurred is postulated to be regulated by an intraluminal, low-affinity receptor. After obtaining T1, the critical concentration of Ca2+ required extraluminally (T2) was determined. T1 averaged 58.6 +/- S.D., 6.9 nmol Ca2+/mg SR and T2 averaged 2.14 +/- S.D., 0.24 microM. Both T1 and T2 were increased by Mg2+ and decreased by caffeine. Ruthenium red increased T2 more than T1 while ryanodine had no effect on T1 but markedly increased T2. The results suggest that two Ca2+ regulatory sites may be functional for Ca2(+)-induced Ca2+ release from SR.
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