Ca2+ uptake coupled to glycogen phosphorolysis in the glycogenolytic-sarcoplasmic reticulum complex from rat skeletal muscle.
The glycogenolytic-sarcoplasmic reticulum complex from rat skeletal muscle accumulates Ca2+ upon stimulation of glycogen phosphorolysis in the absence of added ATP. It is shown that an efficient Ca2+ uptake involves the sequential action of glycogen phosphorylase, phosphoglucomutase and hexokinase, which generate low concentrations of ATP (approximately 1-2 microM) compartmentalized in the immediate vicinity of the sarcoplasmic reticulum Ca2+, Mg(2+)-ATPase (the Ca2+ pump). The Ca2+ uptake supported by glycogenolysis in this subcellular structure is strongly stimulated by micromolar concentrations of AMP, showing that the glycogen phosphorylase associated with this complex is in the dephosphorylated b form. The results point out that the flux through this compartmentalized metabolic pathway should be enhanced in physiological conditions leading to increased AMP concentrations in the sarcoplasm, such as long-lasting contractions and in ischemic muscle.
Nogues
M
M
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain.
Cuenda
A
A
Henao
F
F
Gutiérrez-Merino
C
C
D000249:Adenosine Monophosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D006003:Glycogen; D006005:Phosphorylases; D006593:Hexokinase; D000251:Adenosine Triphosphatases; D000252:Calcium-Transporting ATPases; D002118:Calcium