Localized reductions in the expression of connexin‐43 are associated with segmental boundaries in the guinea pig ileum

Abstract

The segmental nature of the gastrointestinal tract has long been appreciated yet the mechanisms that contribute to segmentation are not understood. Video analysis of isolated segments of guinea pig ileum during luminal infusion revealed a consistent model of emptying contractions comprised of five phases: 1) contraction oral of a point of stimulation (POS) with distension of the tissue anal to the POS; 2) immediately followed by a secondary contraction that encompassed a large segment of ileum; 3) a segmental boundary (SB) on which the secondary contraction stalled; 4) contraction in the segment anal to the SB; and 5) distension segmentally by incoming and/or backflow fluid. Locations of the POS and SB were consistent within a single preparation prompting structural analysis. Because the peristaltic reflex is initiated at the POS, some tissues were labeled NeuN, a marker for intrinsic afferent neurons. There were no differences between the proportions of NeuN-positive cells at the POS and the region of secondary contraction. While terminal fields of long-descending interneurons (5-HT- or somatostatin-immunoreactive baskets) were not different at the SB, the SB contained less connexin-43 than the region of the secondary contraction and the proportion of all kit-positive voxels in the DMP that contained connexin-43 was less at the SB (2.8 ± 0.6%) than in the region of secondary contraction (4.7 ± 1.1%). Collectively, these data indicate that segmental boundaries contain less connexin-43 and suggest that dynamic levels of gap junction proteins in ICC and smooth muscle may underlie the segmental nature of the intestine. Supported by DK76665