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Intracellular pH of in vitro diaphragm preparations was determined following low- (5 Hz, 1.5 min) and high- (75 Hz, 1 min) frequency stimulation, using glass microelectrodes of the liquid membrane type (pHm). Results were compared with values obtained by the standard homogenate technique (pHh). High- and low-frequency stimulation reduced peak tetanic(More)
Our purpose is to summarize the major effects of space travel on skeletal muscle with particular emphasis on factors that alter function. The primary deleterious changes are muscle atrophy and the associated decline in peak force and power. Studies on both rats and humans demonstrate a rapid loss of cell mass with microgravity. In rats, a reduction in(More)
Slow oxidative (SO) fibers of the adductor longus (AL) were predominantly damaged during voluntary reloading of hindlimb unloaded (HU) rats and appeared explainable by preferential SO fiber recruitment. The present study assessed damage after eliminating the variable of voluntary recruitment by tetanically activating all fibers in situ through the motor(More)
1. Intramembrane charge movements and changes in intracellular Ca2+ concentration (Ca2+ transients) elicited by pulse depolarization were measured in frog fast twitch cut muscle fibres under voltage clamp. 2. Extracellular solutions with very low [Ca2+] and 2 mM-Mg2+ , shown in the previous paper to reduce Ca2+ release from the sarcoplasmic reticulum (SR),(More)
The purpose of this study was to describe the alterations in the intracellular concentrations of sodium ([Na+]i) and potassium ([K+]i) and the membrane potential (Em) as a result of fatiguing stimulation of the frog semitendinosus muscle and to relate these changes to the alterations in the sarcolemma action potential and force-generating ability of the(More)
Manifestations of excitation-contraction (EC) coupling of skeletal muscle were studied in the presence of metal ions of the alkaline and alkaline-earth groups in the extracellular medium. Single cut fibers of frog skeletal muscle were voltage clamped in a double Vaseline gap apparatus, and intramembrane charge movement and myoplasmic Ca2+ transients were(More)
This study was undertaken to evaluate the relationship between physical performance capacity and the mitochondrial content of skeletal muscle. Four groups of rats were trained by means of treadmill running 5 days/wk for 13 wk. One group ran 10 min/day, a second group ran 30 min/day, a third group ran 60 min/day, and a fourth group ran 120 min/day. The(More)
The causative factors in muscle fatigue are multiple, and vary depending on the intensity and duration of the exercise, the fibre type composition of the muscle, and the individual's degree of fitness. Regardless of the aetiology, fatigue is characterized by the inability to maintain the required power output and the decline in power can be attributed to a(More)
The purposes of this study were to characterize the alterations in the sarcolemma action potential (AP) waveform and sarcolemma excitability as a result of fatiguing stimulation of the frog semitendinosus muscle and to relate these changes to the decrease in the force-generating ability of the muscle. Trains of APs were recorded before and after stimulation(More)