The development of tetrodotoxin-resistant action potentials in long-term organ culture of rat muscle.

The development and long-term maintenance of tetrodotoxin (TTX)-resistant action potentials in culture was examined. The amplitude and maximum rate of rise of the action potential in normal Ringer solution fell during culture. At the same time the amplitude and maximum rate of rise of the TTX-resistant action potential increased, demonstrating that TTX resistance can develop fully in culture. Actinomycin D inhibited the onset of denervation changes in culture and was also able to delay the fall in the maximum rate of rise of the action potential in normal Ringer solution. When applied to muscle after 48 h of culture, it was relatively ineffectual, showing that de novo protein synthesis during the first 48 h of culture result in denervation changes which are not reversed by subsequent exposure to actinomycin D. The onset of TTX resistance occurred more rapidly in dissociated muscle fibres, presumably as a result of the early removal of the nerve stump.