Migrating motor complexes do not require electrical slow waves in the mouse small intestine

We have investigated whether migrating motor complexes (MMCs) are impaired or absent in the small intestine of W/W-v mutant mice, which lack pacemaker interstitial cells of Cajal (ICC) and electrical slow waves. The intracellular electrical and mechanical activities of the small intestines of wild-type (+/+) and W/W-v mutant mice were recorded. Electrical recordings from circular muscle cells confirmed the absence of slow waves in W/W-v mice, whereas slow waves were always recorded from +/+ muscle cells. Spontaneous phasic contractions were recorded from W/W-v muscles in the absence of slow waves, but these events occurred at a lower frequency than in +/+ tissues. MMC activity was recorded consistently from the ileum of +/+ mice, and normal MMCs were also recorded from W/W-v mice. MMCs in both +/+ and W/W-v mice were abolished by tetrodotoxin (I muM), hexamethonium (300 muM) or atropine (I muM), suggesting that the neural control mechanisms responsible for MMCs in +/+ mice are intact and are responsible for MMCs in W/W-v mice. Transmural nerve stimulation demonstrated intact inhibitory and excitatory neural regulation of W/W-v intestinal muscles. Prolonged trains of cholinergic motor nerve stimulation failed to activate slow waves in the intestinal muscles of W/W-v mice. Our findings show that the generation and directional propagation of MMC activity in mouse small intestine does not require slow-wave activity or an intact network of myenteric ICC. The generation and propagation of MMCs appear to be an intrinsic capability of the enteric nervous system and are not related to slow waves or the gradient in slow-wave frequency.