Abstract
Motilin, a 22 amino acid peptide, is reported to be a key factor in controlling the interdigestive migrating contractions of the gastrointestinal tract. Erythromycin (EM) and its derivatives are known as nonpeptide motilin agonists. In fact, they induce gastrointestinal contractions similar to those observed during the interdigestive migrating contractions. Although their actions on either nerve tissues or gut smooth muscles are reported, mechanisms and sites of their actions have not been fully understood. The present electrophysiological experiments were made to examine actions of EM as well as motilin in the myenteric plexus of the guinea-pig ileum removed after 18 h-fasting. Intracellular recordings were made from myenteric neurons using glass microelectrodes, and focal electrical stimulation was given to evoke fast EPSPs characteristic of S neurons. EM and motilin (up to 1 μM) applied by superfusion caused membrane depolarizations in a proportion of S neurons and in a few AH neurons. EM inhibited fast EPSPs in amplitude; this inhibition of fast EPSPs was often accompanied with EM-induced depolarizations. When the EM depolarizations were eliminated manually by passing inward currents, fast EPSPs were confirmed to be inhibited in the presence of EM. It should be added that motilin also depressed fast EPSPs without changing postsynaptic nicotinic sensitivity. It was concluded that EM might inhibit synaptic transmission in the myenteric plexus possibly by acting presynaptically as a motilin agonist. [Jpn J Physiol 54 Suppl:S198 (2004)]
