Evidence supporting presence of two pacemakers in rat colon

Intracellular microelectrodes and organ bath techniques were used to study spontaneous cyclic electrical and mechanical activity in the rat colon. Ele ctron microscopy and immunohistochemical studies showed two major populatio ns of interstitial cells of Cajal (ICC): one associated with Auerbach's ple xus (ICC-AP) and one with the submuscular plexus (ICC-SMP). The ICC-SMP net work partly adhered to the submucosa when removed and was generally strongl y damaged after separation of musculature and submucosa. Similarly, longitu dinal muscle removal severely damaged AP. Two electrical and mechanical act ivity patterns were recorded: pattern A, low-frequency (0.5-1.5 cycles/min) , high-amplitude oscillations; and pattern B, high-frequency (13-15 cycles/ min), low-amplitude oscillations. Pattern A was recorded in preparations wi th intact AP but absent in those without intact AP. Pattern B was recorded in preparations with intact SMP but was absent in those lacking SMP. With f ull-thickness strips, the superimposed patterns A and B were recorded in ci rcular muscle. When longitudinal muscle mechanical activity was recorded, o nly pattern A was present. We conclude that two pacemakers regulate rat col onic cyclic activity: the ICC-SMP network (responsible for cyclic slow wave s and small-amplitude contractions) and the ICC-AP network (which may drive the cyclic depolarizations responsible for high-amplitude contractions). T his is the first report showing consistent slow wave activity in the rodent colon.