On the repetitive discharge in myotonic muscle fibres

1. Muscle fibres from myotonic goats respond to injected constant currents with a train of action potentials. If the number of action potentials in an evoked train exceeds 10-15, stopping the current does not stop the repetitive firing of action potentials.2. Normal muscle fibres (goat) in a chloride-free Ringer respond in the same way to constant current.3. In the absence of self-maintained activity both myotonic fibres and normal fibres in chloride-free Ringer show an after-depolarization which is proportional to the number of driven impulses. The half-time for the decay of this after-potential is about 0.5 sec.4. Tubular potassium accumulation resulting from the initially driven activity and the known low chloride conductance of myotonic muscle fibres appear to account for the initiation of the myotonic discharge.