Contractile characteristics of the flexor muscle of mice infected with Trichinella spiralis, T. nativa or T. pseudospiralis

A comparative analysis of skeletal muscle isometric contractile characteristics was performed in vivo on the flexor muscle of mice infected 6 mo earlier with 400 larvae of Trichinella pseudospiralis, Trichinella spiralis, or Trichinella nativa. The control group consisted of age- and sex- matched uninfected mice. The mice were injected with 0.1 ml of 50% urethane in saline, and the skin of the left hind limb was cut open longitudinally. The exposed flexor muscle was freed from the adjacent tissue and left attached freely to the knee joint while the tendon was hooked to a transducer. The signals were amplified with an amplifier connected to a chart recorder. The sciatic nerve was exposed and attached to an electrode. Impulses were generated and muscle contraction recorded. The exposed muscle and nerve were bathed in normal Krebs solution at all times and the animals were kept alive during the experiment. The normal muscle twitch tension of uninfected mice reached an average of 2.26 ± 0.24 (SD) g. Tetany was achieved at 15 Hz. Low-Ca²⁺ Krebs depressed the twitch tension to 2.0 ± 0.08 g while tetany remained at 15 Hz. Muscle twitch tension in mice infected with T. pseudospiralis reached 2.47 ± 0.17 g and tetany at 15 Hz. Low Ca²⁺ depressed twitch tension to 1.14 ± 0.12 g. Tetany was achieved at 20 Hz. In contrast, the muscle twitch of mice infected with T. nativa was significantly reduced to 1.4 ± 0.09 g and tetany at 15 Hz. Low Ca²⁺ depressed twitch tension to 0.9 ± 0.16 g and tetany at 15 Hz. Two mice did not show any twitch tension and 1 mouse reach tetany at 6 Hz. Similarly, in T. spiralis- infected mice, muscle twitch tension was markedly down to an average of 0.85 ± 0.09 g. Three mice reached tetany at 25 Hz, 2 at 65 Hz, and 2 at 70 Hz; 3 mice did not show any twitch tension in low-Ca²⁺ Krebs. In those that showed recovery, twitch tension reached 0.675 ± 0.0433 g. Thus, muscle twitch tension in mice infected with T. pseudospiralis was not significantly different from the control group. However, in the case of mice infected with T. nativa or T. spiralis, muscle twitch was reduced by 38.1% and 62.3%, respectively.