Origin of slow waves in the isolated proximal colon of the cat

Slow oscillations of the membrane potential difference of circular smooth muscle cells of the colon, slow waves, arise at the interface between the submucosa and muscularis externa of the colon. These studies test the hypothesis that the generation of slow waves in the circular muscle layer of the colon of the cat is dependent upon an intact interface between the submucosa and muscularis externa. Electrical recordings were made from 3 types of tissue preparations from the proximal colon: (a) submucosa and muscularis externa intact, (b) submucosa isolated from the circular muscle, and (c) muscularis externa isolated from the submucosa. The cellular make-up of each tissue was determined by the osmic acid-zinc iodide method (Champy-Maillet), and the Masson's trichrome stain. Continuous slow waves were recorded from intact tissues. Removal of the submucosa abolished slow waves from the underlying muscularis externa. Either irregular electrical transients or waxing and waning slow wave-like activity were recorded from the isolated submucosa. Submucosal tissues removed from the muscularis externa contained no circular smooth muscle, but did contain elements of the plexus submucosus extremus.