REGULATION OF THE FREQUENCY OF MYOELECTRIC COMPLEXES IN THE ISOLATED MOUSE COLON

Intracellular recordings were made from the circular muscle layer of t he isolated mouse colon in the presence or absence of 2 muM nifedipine at 37-degrees-C. Slow waves were recorded in about 35% of preparation s and were up to 20 mV in amplitude when recorded from cells close to the submucous plexus. Myoelectric complexes were also recorded and con sisted of cholinergic (hyoscine sensitive) rapid oscillations (approxi mately 2 Hz) superimposed on slow depolarizations (approximately 17 mV ) in membrane potential (resting membrane potential approximately 51 m V) occurring every 80 to 410 seconds. In recordings made simultaneous ly using 2 microelectrodes, aborally migrating complexes were observed in all preparations whilst, in approximately half of these preparatio ns, some complexes migrated orally or were stationary. The intervals b etween complexes were increased by reducing the size of the preparatio n and by the addition of 1 muM hyoscine. Pirenzipine (50 nM) also incr eased the interval between complexes without affecting the cholinergic rapid oscillations. The addition of 5-hydroxytryptamine (10 muM) init iated a premature complex and decreased the intervals between complexe s in the presence or absence of hyoscine. These studies have shown tha t the intervals between myoelectric complexes recorded in vitro can be increased or decreased by pharmacologically active substances, probab ly by modifying neural control processes in the enteric nervous system .