Rest tension-based characterization of isometric contractility of Bufo gastrocnemius ex vivo / 南方医科大学学报

<p><b>OBJECTIVE</b>To characterize the isometric contractility of Bufo gastrocnemius ex vivo in light of the rest tension.</p><p><b>METHODS</b>Bufo gastrocnemius treated with SOD inhibitor and ascorbate was stimulated electrically (12 V DC, 2 ms duration with a 2 s interval) to record the tension within 10 min. Weighted fitting to the relaxation curve of the tension below 90% of the peak tension with a mono-exponential model yielded the rest tension and relaxation rate.</p><p><b>RESULTS</b>The control gastrocnemius showed monotonic decrease of the rest tension, but treatment with SOD inhibitor and ascorbate resulted in a decrease of the rest tension followed by a fast increase within a 1.0 min contraction. The increase of the rest tension at 7.0 min of contraction of the treated muscle was significantly greater than that of the control muscle. The control muscle showed a monotonic decrease of the relaxation rate in 10 min, whereas treatment with SOD inhibitor and ascorbate produced increased relaxation rate followed by monotonic decrease till a plateau was reached. In the course of the 10 min recording, the relaxation rate of the treated muscle was lower than that of the control after the same duration of contraction.</p><p><b>CONCLUSION</b>Rest tension is a characteristic index to represent the skeletal muscle contractility.</p>

Effects of ascorbic acid on relaxation of ex vivo Bufo gastrocnemius during sustained isometric contraction / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the effect of ascorbic acid (VC) on relaxation of ex vivo Bufo gastrocnemius during sustained isometric contraction.</p><p><b>METHODS</b>Dynamic tension of the muscle was recorded under constant voltage stimulation within 7.0 min at 2 s intervals. The rest tension and relaxation rate of the muscle was obtained by weighted fitting to the relaxation process of tension <90% of its peak with a mono-exponential model to characterize the muscular relaxation.</p><p><b>RESULTS</b>VC at 2.0 mmol/L alone or in combination with the inhibitors of the antixoidation enzymes (surperoxide dismutase, glutathione peroxidase and catalase) resulted in negligible alterations in the muscular relaxation kinetics. VC combined with the inhibitor of surperoxide dismutase resulted in significantly lowered relaxation rate while increased rest tension, but VC with the inhibitor of either catalase or glutathione peroxidase showed negligible action. VC combined with the inhibitors of all the 3 enzymes also caused significant effect on the muscular relaxation kinetics, which was similar the effect of VC with superoxide dismutase inhibitor.</p><p><b>CONCLUSION</b>VC at high concentration may result in oxidative toxicity to the biological system rich in transitional metal ion complexes but with low antioxidation capacity by causing superoxide-mediated oxidative damages.</p>