A new model of pacing in the mouse intestine.

A simple model of pacing in mouse intestine to longitudinal (LM) as well as circular muscle (CM) has been developed. Undissected segments of LM or CM from mouse ileum or jejunum were prepared to record contractions, nerve functions were inhibited, and regular spontaneous contractions were recorded. These had the properties expected of interstitial cells of Cajal (ICC) paced contractions: ileum slower than jejunum, inhibited but not abolished by nicardipine, reduced in frequency by cyclopiazonic acid, abolished by Ca(2+)-free media, and high temperature dependence (Q10 approximately 2.6-3.2). Nicardipine significantly reduced the pacing frequency in LM and CM. Intestinal segments from W/W(V) mice had few irregular contractions in CM but had regular contractions in LM. Other differences were found between LM and CM that suggest that the control of pacing of LM differed from pacing of CM. Moreover, both LM and CM segments in wild-type and W/W(V) and after cyclopiazonic acid responded to electrical pacing (50 V/cm, 50 or 100 ms) at 1 pulse per second. Temperature <26 degrees C inhibited electrically paced contractions in CM. These findings suggest that the current models of ICC pacing need to be modified to apply to intact segments of mouse intestine.