Rebound excitation of the smooth muscle cells of the guinea-pig taenia coli after stimulation of intramural inhibitory nerves.

1. A study has been made of the increase in the rate of action potential firing in spontaneously active cells and of the initiation of action potential firing in quiescent cells of the taenia coli after stimulation of the intramural inhibitory nerves.2. In the majority of cells which fired action potentials spontaneously at intervals of about 1 sec, stimulation of the intramural inhibitory nerves with single pulses gave an inhibitory junction potential (I.J.P.) which was followed by action potentials which occurred at intervals as small as 0.5 sec. The increased rate of firing lasted up to 30 sec.3. A small number of cells were either not spontaneously active or only fired action potentials at intervals greater than 5 sec. After stimulation of the intramural inhibitory nerves with either single or repetitive pulses, the quiescent cells gave I.J.P.S which were followed by either a single action potential or a burst of action potentials.4. The rate of firing of action potentials after an I.J.P., and the duration of this enhanced rate of firing increased with an increase in the mean amplitude of the hyperpolarization during the I.J.P. As the amplitude of the I.J.P. increases with an increase in frequency of stimulation of the nerves, the rebound excitation increases with an increase in the frequency of stimulation of the inhibitory nerves.