Chronic stimulation of mammalian muscle: changes in metabolite concentrations in individual fibers.
Single fibers were analyzed from rabbit fast-twitch tibialis anterior muscles freeze-clamped during continuous stimulation at 10 Hz for up to 8 wk. ATP declined after 1 wk to a stable level approximately 30% below controls. Phosphocreatine decreased earlier and to a greater extent (approximately 50%). Glycogen varied considerably among stimulated fibers and decreased on average approximately 75% by 8 wk. Glucose, lactate, citrate, and malate had changed little in the first 30 h and then increased four-, two-, four-, and sevenfold, respectively, over the next 5 wk. Glucose 6-phosphate showed the most unexpected behavior: with an overall upward trend, it descended to extremely low values (10% of control) after approximately 1 wk of stimulation. As long as high- and low-oxidative fibers were present, the former showed slightly higher levels of ATP, lactate, and malate; other metabolites did not differ in a consistent way. These unexpected observations, which differ strikingly from data for acute stimulation, shed light on adaptations that enable a chronically stimulated muscle to sustain a continuous high level of ATP utilization.
Henriksson
J
J
Department of Physiology III, Karolinska Institutet, Stockholm, Sweden.
Salmons
S
S
Chi
M Y
MY
Hintz
C S
CS
Lowry
O H
OH
D000227:Adenine Nucleotides / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002951:Citrates / Q000378:metabolism; D004558:Electric Stimulation; D005260:Female; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism; D008293:Malates / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000294:innervation / Q000378:metabolism / Q000502:physiology*; D010543:Peroneal Nerve / Q000502:physiology; D010725:Phosphocreatine / Q000378:metabolism; D011817:Rabbits
D000227:Adenine Nucleotides; D002951:Citrates; D007773:Lactates; D008293:Malates; D010725:Phosphocreatine; D000255:Adenosine Triphosphate; D006003:Glycogen; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase; D005947:Glucose