Properties of the cat ileocecal sphincter muscle

Abstract

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.

Characterization of nerve-induced relaxation of gastrointestinal sphincteric smooth muscle in a South American opossum (Didelphis albiventris)

“…The fact that TTX raised the tension in the ileocolonic junction but not in the lower esophageal sphincter or pyloric strips indicates the presence of an intrinsic tonic inhibitory innervation in this region. Similar responses were reported in the lower esophageal sphincter of the NA opossum (14) as well as in the ileocolonic junction of the cat and NA opossum (15,16). Since atropine and guanethidine did not affect the basal tension of the ileocolonic junction, such tonic innervation seems to be due to intrinsic NANC nerves as described in the cat and guinea pig (16,17).…”

“…Similar responses were reported in the lower esophageal sphincter of the NA opossum (14) as well as in the ileocolonic junction of the cat and NA opossum (15,16). Since atropine and guanethidine did not affect the basal tension of the ileocolonic junction, such tonic innervation seems to be due to intrinsic NANC nerves as described in the cat and guinea pig (16,17). The isolated strips of the circular muscle obtained from the pyloric region of SA opossums did not develop spontaneous tension but always exhibited regular spontaneous phasic activity.…”

“…Since this opossum species is not readily available to us, in the present study we characterized in vitro the nerve-induced responses of the circular smooth muscle from gastrointestinal sphincters of the closely related opossum species Didelphis albiventris, readily available in SA. Our results show that, as described for isolated strips of circular smooth muscle from the esophagogastric and ileocecal junctions of other species including humans (14)(15)(16)(17)(18)(19)(20)(21), the strips from these regions obtained from the SA opossum developed spontaneous tension which was not influenced by atropine or adrenergic blockers. The fact that TTX raised the tension in the ileocolonic junction but not in the lower esophageal sphincter or pyloric strips indicates the presence of an intrinsic tonic inhibitory innervation in this region.…”

Motor Activity of the Distal Ileum and Ileocecal Sphincter and Its Relation to the Region’s Function

“…Alterations in tone and excitability of ICS muscle strips related to the presence of agents known to influence transmembrane calcium and potassium fluxes [9,13] further support a role for basic membrane properties in the generation of the specialized muscle function of this area. As is the case at other sphincters, this tone is oxygen dependent [12] and persists following neural blockade by tetrodotoxin [14,15] -further evidence for the importance of myogenic factors in its generation. However, inhibition of myo genic activity with a calcium antagonist does not completely abolish tone, suggesting that elastic factors may also contribute [15].…”

“…As is the case at other sphincters, this tone is oxygen dependent [12] and persists following neural blockade by tetrodotoxin [14,15] -further evidence for the importance of myogenic factors in its generation. However, inhibition of myo genic activity with a calcium antagonist does not completely abolish tone, suggesting that elastic factors may also contribute [15]. ICS muscle strips also demonstrate a greater re sistance to stretch than strips from adjacent terminal ileum and colon [14,15] -another sphincteric property [10,11],…”