1. Na-octanoate (in Ringer's solution) affects the membrane resistance of isolated frog skeletal muscle fibres in a biphasic way. Initially there is an increase followed by a more slowly developing decrease. The effect depends on both the concentration of the fatty acid (1-20 mM) and the time of exposure (2-20 min). 2. In muscles exposed either to isotonic K2SO4 or to Ringer's solution with Cl- substituted by methylsulphage, the octanoate-induced resistance drop is the same as in normal Ringer's solution whereas an initial increase is not observed. 3. In Na-free (Tris-) Ringer's solution, only an increase in membrane resistance is caused by octanoate. 4. The results suggest that Na-octanoate decreases the conductance of the resting muscle cell membrane for anions (Cl-1) whereas the permeability for cations (Na+, K+) is increased.
The toxic effect of trichlorethylene (TCE) was investigated on isolated muscles prepared from frog and rats. Twitch and tetanic contractions as well as caffeine-induced contractures, were recorded. Trichloroethylene at a concentration of 0.25-4.0 mM depressed the force development of both twitch and tetanic tension in a dose-dependent manner. This effect was not influenced by the type of muscle. As TCE shortened the time to peak of twitch contractions, it may alter the Ca2+ binding kinetics. Subthreshold caffeine concentrations applied after pre-exposure to TCE (1 or 2mM) induced contractures. The same TCE exposure enhanced regular caffeine contractures through increasing the speed of tension development and the absolute force. Exposure to 5 or 10 mM TCE did not affect the first caffeine-induced contracture but enhanced the potency of the second caffeine dose given 15 min after the first. The results suggest that the interaction of TCE with membrane sites is responsible for Ca2+ release for contractile processes.
Stress fractures may occur after extremely high exercises in sports, military training, and occupational activities. The pathogenetic mechanisms include processes of material fatigue as well as repair capacities of the bone. By means of szintigraphic technique a sensitive tool for diagnostics of stress fractures is available. Recently, stress fractures of the vertebral processes only are acknowledged as a professional disease in Germany. As a rule, in orthopaedic and surgical practice fatigue fractures of other bones are considered as cases of accidental injuries.
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