[Action potentials of the fast and slow muscle fibers of the bog turtle Emys orbicularis].

In skeletal muscles of the tortoise E. orbicularis, fast and slow muscle fibers were found which differ in the lipid content and electrophysiological properties. Fast fibers contain small amounts of lipid inclusions. In response to direct electrical stimulation they produce fast action potentials (AP) which are capable of rhythmic activity during prolonged depolarization. Slow fibers are rich in lipid inclusions. Their AP differs from that of fast fibers by slow onset, and decay, lower gradient of rise, lower amplitude and lower velocity of propagation. These fibers are not capable of rhythmic activity. The data obtained show that with respect to their morphological and physiological properties slow muscle fibers of the tortoise differ from tonic amphibian fibers, but exhibit the most similarity to slow avian fibers.