OBJECTIVETo observe expressions of glucose-regulated protein (GRP78) and caspase-S12 in nervous system-interstitial cells of Cajal (ICC) in smooth muscle in colonic wall in rats with scald injury, as well as their relevant ultrastructural changes, so as to probe the possible mechanisms of dynamic damage in murine colon after a scald injury.

METHODSFifty healthy Sprague-Dawley rats were randomly divided into scald (n = 40) and control (n = 10) groups. Rats in scald group were inflicted with 30% TBSA full-thickness scald, and received an intraperitoneally injection of Ringer lactate solution (50 mg/kg) for resuscitation, while those in control group had similar treatment with the exception of scald. Rats in control group and scald group were sacrificed at 3, 6, 12, 24 post scald hour (PSH, 10 rats at each time point) for collection of 4 cm of colonic tissue, 5 cm proximal to the cecum. A segment of colonic wall, 1 cm in length, was obtained from the middle of the harvested segment of colon, and it was fixed with 3% glutaraldehyde or 10% formaldehyde. The samples fixed with glutaraldehyde were used to observe ultrastructural alterations under transmission electron microscope, while that with formaldehyde were used to observe expressions of GRP78 and caspase-12 in colonic wall by immunohistochemical assay.

RESULTSThe colonic smooth muscle cells of rats in control group showed regular arrangement, their organelles were abundant, nucleus centrally located, euchromatin distributed evenly with more abundant mitochondrial cristae and less smooth endoplasmic reticulum, neuronal organelles were abundant in intermuscular plexus, and ICC could be seen in the neighborhood of neurons. The colonic smooth muscle cells appeared in irregular and disordered manner in scald group, perinuclear space was widened, intercellular vacuoles were observed, mitochondria showed vacuolation degeneration with dissolved and condensed cristae, rough endoplasmic reticula were dilated with partial dissolution, and perinuclear cytoplasm of ICC was obviously decreased. The expression of GRP78 was increased in scald group at 3, 6, 12 PSH (4.3 +/- 0.9, 6.0 +/- 0.7, 4.8 +/- 1.1 score) as compared with that in control group (2.4 +/- 0.7 score, P < 0.05). The expression of caspase-12 in scald group at 6, 12, 24 PSH was higher than that in control group (P < 0.05). GRP78 was consistently expressed in cytoplasm in control group, while in scald group, it mainly appeared in mucosa, myenteric plexus, and stromal cells, but only moderately or lightly expressed in smooth muscle cells. The expression of GRP78 was positive in scald group at 3, 6, 12 PSH, strongly positive at 6 PSH, and it was also expressed in cytoplasm in control group. The expression of caspase-12 in scald group was not obviously positive at 3 PSH, and weakly positive at 6, 24 PSH, but strongly positive at 12 PSH, while no expression was shown in control group.

CONCLUSIONSMarked pathological changes are observed in enteric nervous system-interstitial cells of Cajal-smooth muscle in rats with severe scald injury. It may be related with cellular injuries induced by caspase-12 apoptotic pathways through activated endoplasmic reticulum stress.