title: Responses of fatigable and fatigue-resistant fibres of rabbit muscle to low-frequency stimulation.
abstract: This study investigates early adaptive responses of fast-twitch muscle to increased contractile activity by low-frequency stimulation. Changes in metabolite levels and activities of regulatory enzymes of carbohydrate metabolism were investigated in rabbit tibialis anterior muscle after 24 h of stimulation. In addition, changes elicited during a 5-min lasting acute stimulation experiment were compared between 24-h-prestimulated and contralateral control muscles. Stimulation for 5 min reduced energy-rich phosphates and glycogen, and increased lactate in the control muscle. A transient elevation of fructose 2,6-bisphosphate demonstrated that activation of phosphofructokinase 2 was an immediate response to contractile activity. Prestimulated muscles displayed nearly normal values for ATP, phosphocreatine and glycogen, and did not augment lactate. Increased activities of hexokinase and phosphofructokinase 2 and permanently elevated levels of fructose 2,6-bisphosphate pointed to enhanced glycolysis with glucose as the main fuel in the prestimulated muscle. Isometric tension of the control muscle decreased rapidly a few minutes after the onset of stimulation. In the prestimulated muscles, tension was almost stable, but amounted to only 30%-40% of the initial tension of the control muscle. In view of the fibre type distribution of rabbit tibialis anterior, these findings suggested that a large fibre fraction of the prestimulated muscle, possibly the glycolytic type IID fibres, did not contract. Therefore, the possibility must be considered that the metabolite pattern of the 24-h-stimulated muscle primarily reflected metabolic activities of the contracting, less fatigable fibres, most likely type IIA and type I fibres.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Unitat de Bioquímica, Facultat de Medicina, Universitat de Barcelona, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Cadefau
authors.forename: J
authors.initials: J
authors.lastname: Parra
authors.forename: R
authors.initials: R
authors.lastname: Cussó
authors.forename: G
authors.initials: G
authors.lastname: Heine
authors.forename: D
authors.initials: D
authors.lastname: Pette
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003401:Creatine / Q000378:metabolism; D004558:Electric Stimulation; D005260:Female; D005635:Fructosediphosphates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives*; D005958:Glucosephosphates / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006019:Glycolysis; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism; D011817:Rabbits
chemical_list: D005635:Fructosediphosphates; D005958:Glucosephosphates; D010725:Phosphocreatine; D019298:Glucose-6-Phosphate; C027652:fructose 2,6-diphosphate; D000255:Adenosine Triphosphate; D006003:Glycogen; C016473:glucose-1,6-bisphosphate; D005947:Glucose; D003401:Creatine