Toward a concept of stretch-coupling in smooth muscle. I. Anatomy of intestinal segmentation and sleeve contractions

Motility patterns and their structural basis were studied by video analysis , light and electron microscopy on the physiologically distended gut from n ormal and W/W-v suckling mice and normal adult mice. Empty or diltiazem-rel axed intestine were used as references. In contrast to conventional primary aldehyde fixation, a brief primary fixation with osmic acid before aldehyd es preserved the visible contraction patterns and revealed dynamic increase s in the number of peg-and-socket junctions coupling muscle cells mutually and with interstitial cells of Cajal (ICC). In tissue engaged in segmentati on, the major increase was in the circular muscle and involved the ICC-DMP (integrated in the circular muscle layer at the site of the deep muscular p lexus), whereas the increase during sleeve contractions was in the longitud inal muscle and involved the ICC-AP (located at the site of Auerbach's plex us). The number and distribution of gap junctions were unaffected. Area ana lysis of cell profiles supported the involvement of circular muscle in segm entation, but longitudinal muscle alone in sleeve contractions. The gut of both normal and W/W-v sucklings (and adults) contracted during segmentation at frequencies close to reported slow-wave frequencies. In W/W-v sucklings , ICC-AP were absent whereas ICC-DMP were present in adult configuration. B efore Day 8 pp gap junctions were seen only between ICC-DMP. In the sucklin gs ICC-DMP may be responsible for rapid circumferential coordination and pa cemaking of ring contractions. The geometry, organization, and dynamic regu lation of peg-and-socket junctions strongly suggest a crucial role in coord ination of smooth muscle and pacemakers, probably as stretch sensors, media ting a 'stretch-coupling' in the system. Anat Rec 262:110-124, 2001. (C) 20 01 Wiley-Liss, Inc.