Endurance training effects on the contractile activation characteristics of single muscle fibres from the rat diaphragm.
1. Considerable debate exists as to whether the properties of diaphragm muscles can be modified by training. As the diaphragm is chronically activated during normal respiration, it is of interest to determine whether this muscle is resistant to further modification by exercise. The aim of this study was to investigate the contractile activation characteristics of single skinned muscle fibres from the diaphragm of both CONTROL and TRAINED rats. 2. Male rats were subjected to a 20 week high-intensity endurance exercise training programme that consisted of running on a motorized treadmill, 5 days/week, 90-120 min/day, 27-30 m/min, up a 20 degrees incline. At the conclusion of training, rats were killed with an overdose of ether and costal regions of the diaphragm were removed and stored in a glycerol-based skinning solution at -20 degrees C. 3. Single skinned (membrane-permeabilized) diaphragm muscle fibres were attached to a sensitive force transducer and activated in Ca(2+)- and Sr(2+)-buffered solutions in order to determine relative force-pCa and force-pSr characteristics. Fibres were allocated into discrete groups (population I, population II, intermediate, mixed) on the basis of their physiological (contractile) properties. 4. Population I (slow-twitch) fibres from the diaphragm of TRAINED rats exhibited a reduced sensitivity to Ca2+ (indicating a rightward shift of the force-pCa relationship) compared to those diaphragm fibres from CONTROL animals. An increased number of population II (fast-twitch) fibres were sampled from TRAINED rats, however, training did not affect the activation properties of these fibres.(ABSTRACT TRUNCATED AT 250 WORDS)
Lynch
G S
GS
Department of Physiology, University of Melbourne, Parkville, Victoria, Australia.
Duncan
N D
ND
Campbell
S P
SP
Williams
D A
DA
D000818:Animals; D002118:Calcium / Q000737:chemistry; D003964:Diaphragm / Q000378:metabolism / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D010807:Physical Endurance; D051381:Rats; D013324:Strontium / Q000737:chemistry
D002118:Calcium; D013324:Strontium