Origin, Transmission and Ionic Dependence of Colonic Electrical Slow Waves

Abstract

Mucosa-free strips of cat colon exhibit slow waves from both the circular and longitudinal sides. Slow waves are always recorded from isolated circular muscle, but never from isolated longitudinal muscle. The longitudinal muscle exhibits slow waves only when it is attached to the underlying circular muscle. It appears that slow waves are generated in circular layer and transmitted to longitudinal layer. In preparations obtained by removing circular muscle from over only part of the longitudinal layer, the decrease of slow wave amplitude in longitudinal muscle with increasing distance from the circular fibers is exponential and indicates an electrotonic spread from circular to longitudinal layer. In ‘intact’ strips slow waves are conducted from circular to longitudinal muscle at 9.33 ± 3.32 mm/sec. Colonic slow waves are both calcium and sodium dependent. Calcium is fundamental in inward transport of current with consequent depolarization. Sodium is involved in the genesis of slow waves by its active cyclic extrusion, probably on the repolarization phase.

Key-words:

• Calcium slow waves
• circular muscle slow waves
• colonic motility
• colonic slow waves
• smooth muscle electrophysiology
• sodium pump