title: Regulation of Ca2+ release from sarcoplasmic reticulum in skeletal muscles.
abstract: Ca2+ release from skeletal sarcoplasmic reticulum (SR) could be regulated by at least three mechanisms: 1) Ca2+, 2) calmodulin, and 3) Ca2+/calmodulin-dependent phosphorylation. Bell-shaped Ca(2+)-dependence of Ca2+ release from both actively- and passively-loaded SR vesicles suggest that opening and closing of the Ca2+ release channel could be regulated by [Ca2+o]. The time- and concentration-dependent inhibition of Ca2+ release from skeletal SR by calmodulin was also studied using passively-Ca2+ loaded SR vesicles. Up to 50% of Ca2+ release was inhibited by calmodulin (0.01-0.5 microM); this inhibition required 5-15 min preincubation time. The hypothesis that Ca2+/calmodulin-dependent phosphorylation of a 60 kDa protein regulates Ca2+ release from skeletal SR was tested by stopped-flow fluorometry using passively-Ca2+-loaded SR vesicles. Approximately 80% of the initial rates of Ca(2+)-induced Ca2+ release was inhibited by the phosphorylation within 2 min of incubation of the SR with Mg-ATP and calmodulin. We identified two types of 60 kDa phosphoproteins in the rabbit skeletal SR, which was distinguished by solubility of the protein in CHAPS. The CHAPS-soluble 60 kDa phosphoprotein was purified by column chromatography on DEAE-Sephacel, heparin-agarose, and hydroxylapatite. Analyses of the purified protein indicate that the CHAPS-soluble 60 kDa protein is an isoform of phosphoglucomutase (PGM). cDNAs encoding isoforms of PGM were cloned and sequenced using synthetic oligonucleotides. Two types of PGM isoforms (Type I and Type II) were identified. The translated amino acid sequences show that Type II isoform is SR-form.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, University of Connecticut Health Center, Farmington 06030-1305.
authors.forename: D H
authors.initials: DH
authors.lastname: Kim
authors.forename: Y S
authors.initials: YS
authors.lastname: Lee
authors.forename: A B
authors.initials: AB
authors.lastname: Landry
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D010733:Phosphoglucomutase / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D010750:Phosphoproteins; D010733:Phosphoglucomutase; D002118:Calcium