Induction of action potentials in cultured slow muscle fibres of the frog.

1. Slow muscle fibres of the frog were maintained in a simple organ culture system for up to 28 days at 18 degrees C. Slow fibres cultured for one week resembled innervated fibres in their lack of ability to generate an action potential. 2. By 10 days a few fibres had acquired the action potential mechanism and in muscles cultured for 28 days all slow fibres examined were capable of generating action potentials most of which reached or exceeded 0 mV membrane potential. 3. Slow muscle fibres which were denervated for two weeks in vivo retained their ability to generate overshooting action potentials after 4 weeks of culture. Thus, in the culture system described, slow muscle fibres are capable of developing action potentials and the action potential mechanism in these fibres remains for at least one month in culture.