Intra- and extraluminal sarcoplasmic reticulum membrane regulatory sites for Ca2(+)-induced Ca2+ release.
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.
Department of Anesthesiology, University of Texas Health Science Center, Houston 77030.
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D000704:Analysis of Variance; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013552:Swine
D012430:Ruthenium Red; D012433:Ryanodine; D002110:Caffeine; D008274:Magnesium; D002118:Calcium