CONTRACTILE CHARACTERISTICS OF THE FLEXOR MUSCLE OF MICE INFECTED WITH TRICHINELLA-SPIRALIS, T-NATIVA OR TRICHINELLA-PSEUDOSPIRALIS

A comparative analysis of skeletal muscle isometric contractile charac teristics was performed in vivo on the flexor muscle of mice infected 6 mo earlier with 400 larvae of Trichinella pseudospiralis, Trichinell a spiralis, or Trichinella nativa. The control group consisted of age- and sex-matched uninfected mice. The mice were injected with 0.1 ml o f 50% urethane in saline, and the skin of the left hind limb was cut o pen longitudinally. The exposed flexor muscle was freed from the adjac ent tissue and left attached freely to the knee joint while the tendon was hooked to a transducer. The signals were amplified with an amplif ier connected to a chart recorder. The sciatic nerve was exposed and a ttached to an electrode. Impulses were generated and muscle contractio n recorded. The exposed muscle and nerve were bathed in normal Krebs s olution at all times and the animals were kept alive during the experi ment. The normal muscle twitch tension of uninfected mice reached an a verage 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 rem ained at 15 Hz. Muscle twitch tension in mice infected with T. pseudos piralis reached 2.47 +/- 0.17 g and tetany at 15 Hz. Low Ca2+ depresse d 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 signif icantly reduced to 1.4 +/- 0.09 g and tetany at 15 Hz. Low Ca2+ depres sed 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. Similar ly, in T. spiralis-infected mice, muscle twitch tension was markedly d own 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 reac hed 0.675 +/-: 0.0433 g. Thus, muscle twitch tension in mice infected with T. pseudospiralis was not significantly different from the contro l group. However, in the case of mice infected with T. nativa or T. sp iralis, muscle twitch was reduced by 38.1% and 62.3%, respectively.