Endurance Training Effects on the Contractile Activation Characteristics of Single Muscle Fibres From the Rat Diaphragm

Abstract

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)

The magnitude of the initial injury induced by stretches of maximally activated muscle fibres of mice and rats increases in old age.

“…Subsequently, anaesthetized rats were killed with an intravenous injection of 1 M KCl. Each muscle was dissected into small fibre bundles which were stored at -20°C in skinning solution containing 125 mm potassium propionate, 5 mm EGTA, 2 mM ATP, 2 mm MgCl2, 20 mm imidazole, and 50% (v/v) glycerol (Lynch, Duncan, Campbell & Williams, 1995). The solution was adjusted to pH 7 with KOH.…”

Skeletal and Cardiac Muscle Ergogenics and Side Effects of Clenbuterol Treatment

“…This transition towards a more glycolytic profile is not only metabolic (glycolytic or oxidative) but also structural with changes in the MHC isoform composition and therefore in the contractile properties of the muscle [96]. These phenotypic changes usually occur during muscle development [97], following a protocol of electrical stimulation at high frequencies [98] during denervation or hormonal changes [99], while reducing load during a simulated loss of gravity during muscle regeneration [7] and in a more limited manner following a training protocol [100,101].…”