Skeletal muscle endurance: the effect of increased availability of endogenous long-chain fatty acid fuel.
A possible role of intramuscularly derived fatty acid fuel on muscle endurance was investigated in curarized diaphragms of fasted rats. These showed significantly improved endurance during 60 min of intermittent stimulation at 20 Hz in vitro compared with diaphragms of fed control animals. The improved endurance appeared to be related to an increased availability and utilization of fatty acid fuel derived from greatly increased numbers of lipid globules in muscle fibers of fasted animals. The pH of muscles with improved endurance (fasted rats) was not different from that of muscles from fed controls at rest. After 60 min of intermittent stimulation, the muscle pH diminished to the same extent in both groups. Diaphragms of fasted rats that were refed 12 h before testing did not show improved endurance. Epinephrine in the bath abolished the improved endurance of diaphragms of fasted rats. Diaphragms of fasted guinea pigs did not show significantly improved endurance (despite abundant intracellular lipid globules), possibly because of a reduced intracellular carnitine.
D000818:Animals; D003964:Diaphragm / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D004558:Electric Stimulation; D005227:Fatty Acids / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D008049:Lipase / Q000378:metabolism; D009132:Muscles / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D010807:Physical Endurance; D051381:Rats; D011919:Rats, Inbred Strains
D005227:Fatty Acids; D006003:Glycogen; D008049:Lipase