PubMedID: 9227789The aim of the study was to investigate whether Na+ channels play a role in the twitch component of the response of the isolated frog rectus abdominis to Ca2+-free Ringer solution with 0.2mM Na2EDTA by using tetrodotoxin and some other well known drugs that exhibit a blocking action on Na+ channels. In the presence of 5 × 10-7M tetrodotoxin, the twitch component, measured isotonically, disappeared. Although 10-7 M d-tubocurarine was found to be ineffective, a complete blockage of twitch amplitude was observed at 5 × 10-6M concentration of the drug. The inhibitory action of d-tubocurarine on twitch response was not antagonized by 10-6 and 10-5 M carbachol. Propranolol (10-6 - 10-5M), lidocaine (2 × 10-6 - 10-5M), quinine (10-6 - 2 × 10-5M) and quinidine (10-6 - 2 × 10-5M) inhibited maximal twitch amplitude in a concentration dependent manner. These findings strongly suggest that activation of tetrodotoxin sensitive Na+ channel may play a primary role at twitch generation during exposure of the frog rectus abdominis to Ca2+-free Ringer solution with Na2 EDTA
