Properties of the cat ileocecal sphincter muscle

The purpose of this study was to determine the length-tension properties and the response to neurohumoral agents of the feline ileocecal sphincter (ICS) circular smooth muscle in vitro. The ICS muscle during stretch maintained a higher resting tension at lower degrees of stretch than did the adjacent ileum and colon. Sodium nitroprusside (10(-3) M) or calcium-free Krebs solution with EGTA (5.0 mM) reduced the resting tension of ICS muscle by 15.8 +/- 2.1 and 19.1 +/- 2.5%, respectively. The ICS response to KCl depolarization was lower (0.37 +/- 0.03 kg/cm2) than colonic muscle (0.55 +/- 0.06 kg/cm2) oe ileal muscle (0.51 +/- 0.04 kg/cm2) (P less than 0.05). However, in response to acetylcholine, ICS muscle tension was minimal (0.06 +/- 0.02 kg/cm2) was compared with the colon (0.49 +/- 0.05 kg/cm2) or ileum (0.53 +/- 0.05 kg/cm2) (P less than 0.01). The ICS muscle contracted in response to phenylephrine, whereas other muscles were inhibited. Secretin, gastrin, glucagon, and cholecystokinin failed to act on the ICS muscle while other muscles did respond. These studies suggest that ICS muscle differs from adjacent ileal and colonic circular muscle in that a) in response to stretch it develops a high resting tension that is relatively resistant to calcium withdrawal, and b) it also shows quantitative and qualitative differences in response to neurohumoral agents.