Ca2+-activation characteristics of single fibres from chemically skinned rat muscle incubated with glucose-6-phosphate.
In this study we examined the effects of 3-24 h of incubation of chemically skinned rat fast-twitch muscle with the glycolytic metabolite glucose 6-phosphate (G6-P) on the contractile properties and myosin ATPase activity in single muscle fibres, and on the carbohydrate content of myosin heavy chains (MHCs). Exposure of the permeabilised muscle to 10 mM G6-P for 24 h at 22+/-1 degrees C in a rigor solution containing protease inhibitors and a reducing agent (dithiothreitol, DTT) significantly decreased maximum Ca(2+)-activated force output by 31%, lowered the Ca2+ threshold for contraction by 0.1 pCa units and produced shallower force-pCa curves compared with controls. Furthermore, under these conditions, G6-P-treated muscle displayed lower myofibrillar MgATPase activity and a markedly higher carbohydrate content of MHCs, as identified with an immunoblot protocol for glycoprotein detection. Shorter incubations under the same conditions or 24-h incubations with 5 mM G6-P generally resulted in smaller changes in the contractile activation parameters. These findings suggest that reducing sugars acting as metabolic intermediates in the glycolytic pathway can have important non-energy-related effects on the contractile activation characteristics of mammalian skeletal muscle. These effects are consistent with the glycation of muscle proteins, in particular that of the MHC.
Patterson
M F
MF
School of Zoology, Faculty of Science and Technology, La Trobe University, Bundoora, Victoria, Australia. M.Patterson@zoo.latrobe.edu.au
Stephenson
D G
DG
Kemp
J G
JG
Stephenson
G M
GM
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002241:Carbohydrates / Q000032:analysis; D019298:Glucose-6-Phosphate / Q000494:pharmacology*; D006652:Histological Techniques; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009210:Myofibrils / Q000201:enzymology; D018995:Myosin Heavy Chains / Q000737:chemistry; D051381:Rats; D020318:Rats, Long-Evans; D012016:Reference Values; D012518:Sarcomeres / Q000648:ultrastructure
D002241:Carbohydrates; D019298:Glucose-6-Phosphate; D000251:Adenosine Triphosphatases; D018995:Myosin Heavy Chains; D002118:Calcium