Regulation of the frequency of myoelectric complexes in the isolated mouse colon

Intracellular recordings were made from the circular muscle layer of the isolated mouse colon in the presence or absence of 2 μM nifedipine at 37°C. Slow waves were recorded in about 35% of preparations and were up to 20 mV in amplitude when recorded from cells close to the submucous plexus. Myoelectric complexes were also recorded and consisted of cholinergic (hyoscine sensitive) rapid oscillations (∼2 Hz) superimposed on slow depolarizations (∼17 mV) in membrane potential (resting membrane potential ‐51 mV) occurring every 80 to 410 seconds. In recordings made simultaneously using 2 microelectrodes, aborally migrating complexes were observed in all preparations whilst, in approximately half of these preparations, some complexes migrated orally or were stationary. The intervals between complexes were increased by reducing the size of the preparation and by the addition of 1 μM hyoscine. Pirenzipine (50 nM) also increased the interval between complexes without affecting the cholinergic rapid oscillations. The addition of 5‐hydroxytryptamine (10μM) initiated a premature complex and decreased the intervals between complexes in the presence or absence of hyoscine. These studies have shown that the intervals between myoelectric complexes recorded in vitro can be increased or decreased by pharmacologically active substances, probably by modifying neural control processes in the enteric nervous system.