We test the hypothesis that cytosolic inorganic phosphate (Pi) can account for the contraction-induced reductions in twitch duration which impair summation and cause force to decline (sag) during unfused tetanic contractions of fast-twitch muscle. A five-state model of crossbridge cycling was used to simulate twitch and unfused tetanic contractions. As Pi concentration ([Pi]) was increased from...

BARNARD, R. JAMES, V. REGGIE EDGERTON, TETSUO FURUKAWA, AND J. B. PETER. Histochemical, biochemical, and contractile properties of red, white, and intermediate jibers. Am. J. Physiol. 220 (2) : 41 O-41 4. 197 1 .-Individual fibers from guinea pig muscles (soleus, flexor hallucis longus (FHL), flexor digitorium longus (FDL), medial gastrocnemius (MG) and the portion of the vastus lateralis (RV) ...

Calorie restriction (CR) induces enhanced insulin-stimulated glucose uptake in fast-twitch (type II) muscle from old rats, but the effect of CR on slow-twitch (type I) muscle from old rats is unknown. The purpose of this study was to assess insulin-stimulated glucose uptake and phosphorylation of key insulin signaling proteins in isolated epitrochlearis (fast-twitch) and soleus (slow-twitch) mu...

Objective(s): Previous studies showed that skeletal muscle microcirculation was reduced in chronic heart failure. The aim of this study was to investigate the effects of endurance training on capillary and arteriolar density of fast and slow twitch muscles in rats with chronic heart failure. Materials and Methods: Four weeks after surgeries (left anterior descending (LAD) artery occlusion), chr...

We used intact fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles from rats and mice to test the hypothesis that exogenous application of an oxidant would increase maximum isometric force production (P(o)) of slow-twitch muscles to a greater extent than fast-twitch skeletal muscles. Exposure to an oxidant, hydrogen peroxide (H(2)O(2); 100 microM to 5 mM, 30 min), affecte...

We utilized quantitative freeze-fracture electron microscopy to study the plasticity of orthogonal clusters of 60-A particles (the “square array”) found in the sarcolemma of fast-twitch muscle. The membrane macromolecular composition of normally slow-twitch rat soleus muscle was examined 1 year after surgical reinnervation by the nerve from fast-twitch extensor digitorum longus muscles. The iso...

Intensive exercise is associated with a pronounced increase in extracellular K+ ([K+]o). Because of the ensuing depolarization and loss of excitability, this contributes to muscle fatigue. Intensive exercise also increases the level of circulating catecholamines and lactic acid, which both have been shown to alleviate the depressing effect of hyperkalemia in slow-twitch muscles. Because of thei...