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. 1990 Apr 24;263(2):292-4.
doi: 10.1016/0014-5793(90)81396-6.

Intra- and extraluminal sarcoplasmic reticulum membrane regulatory sites for Ca2(+)-induced Ca2+ release

T E Nelson  1 , K E Nelson
Affiliations
Free article

Intra- and extraluminal sarcoplasmic reticulum membrane regulatory sites for Ca2(+)-induced Ca2+ release

T E Nelson et al. FEBS Lett. .
Free article

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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