[Alteration of Ca2+ mobilization and increased circular muscle contractility in colon of stressed rats].

Objective: To investigate relationship between the cold-restraint stress induced colonic circular muscle contractility disorder and calcium-handling properties alteration of the affected muscle in rats.

Methods: Stress was conducted on rats to induce the fecal pellet output increased. Contractile responses to acetylcholine (Ach), KCl, and NaF were determined for colonic circular muscle. To investigate Ca(2+) mobilization, effects of Ca(2+)-free solution, high concentration of extracellular Ca(2+), and pinaverium bromide on the contractility of colon were determined. Prepared sarcoplasmic reticular (SR) of colonic muscle by differential centrifugation and measured Ca(2+)-ATPase activity with colorimetric assay.

Results: In stressed rats, contractile responses of colonic circular muscle to Ach, KCl, and NaF increased significantly; the contraction was more sensitive to high concentration of extracellular Ca(2+) than control. In Ca(2+)-free solution, contractions were significantly suppressed in both groups. Pinaverium dose-dependently blocked contractions acting with different sensitivity on the two preparations. The Ca(2+)-ATPase activity of the SR in stress was lower than control.

Conclusions: Cold- restraint stress caused a marked increase in the contractility of the colonic circular muscle in rats. Stressed rats' colonic muscle shows an alteration in the homeostasis of intracellular Ca(2+), with appears to be the consequence of increased influx of extracellular Ca(2+), decreased release of intracellular stores of Ca(2+) and a decreased Ca(2+)-ATPase activity of the SR.