TTX, cations and spider venom modify avian muscle tone in vitro.

Agents that reduce skeletal muscle tone may have a number of useful clinical applications, e.g., for muscle spasticity and other muscle disorders. Recently, we reported that the venoms of two species of Australian theraphosid (Araneae, Theraphosidae) spiders (Coremiocnemis tropix and Selenotholus foelschei) reduced the baseline tension of chick biventer cervicis nerve-muscle preparation. The purpose of this study was to determine the underlying physiology mediating the change in muscle tension, which was addressed by conducting isometric tension experiments. We found that MgCl(2) (20mM), CaCl(2) (20mM), tetrodotoxin (1μM) or C. tropix venom (2μl/ml) produced a similar decrease in baseline tension, whereas d-tubocurarine (100μM), gadolinium (1mM), verapamil (10mM), an increase in osmotic pressure by the addition of glucose (40mM), or the presence/absence of electrical stimulation did not produce a significant change in baseline tension. We suggest that mechanosensitive or muscle TTX-sensitive sodium channels are activated during muscle stretch. This may have implications for the treatment of stretch induced muscle damage.