Action potential generation in the small intestine of W mutant mice that lack interstitial cells of Cajal

The small intestine of Wi / W-upsilon mice lacks both the network of interstitial cells of Cajal (ICC), associated with Auerbach's plexus, and pacemaker activity, i.e., it does not generate slow-wave-type action potentials. The W / W-upsilon muscle preparations showed a wide variety of electrical activities, ranging from total quiescence to generation of action potentials at regular or irregular frequency with or without periods of quiescence. The action potentials consisted of a slow component with superimposed spikes, preceded by a slowly developing depolarization and followed by a transient hyperpolarization. The action potentials were completely abolished by L-type Ca2+ channel blockers. W / W-upsilon mice responded to K+ channel blockade (0.5 mM Ba2+ or 10 mM tetraethylammonium chloride) with effects on amplitude, frequency, rate of rise, and duration of the action potentials. In quiescent tissues from W / W-upsilon mice, K+ channel blockade evoked the typical spikelike action potentials. Electron microscopy identified few methylene blue-positive cells in the W / W-upsilon small intestine associated with Auerbach's plexus as individual ICC. Numbers of resident macrophage-like cells (MLC) and fibroblast-like cells (FLC) were significantly changed. Neither FLC nor MLC were part of a network nor did they form specialized junctions with neighboring cells as ICC do. Hence no cell type had replaced ICC at their normal morphological position associated with Auerbach's plexus. ICC were present in W / W-upsilon mice at the deep muscular plexus in normal organization and numbers, indicating that they are not dependent on the Kit protein and do not take part in generation of pacemaker activity.