Abstracts
2001 Digestive Disease Week

# 1760 Ulcerative Colitis and H2O2-Induced Smooth Muscle Dysfunction
Matthew D. Vrees, Weibiao Cao, Fabio M Potenti, Piero Biancani, Victor E. Pricolo, Providence, RI, Cranston, RI

Purpose: In normal sigmoid colon smooth muscle cells, exposure to IL-1b can reproduce changes in contractile function observed in ulcerative colitis (UC). These changes may be secondary to increased concentration of H₂O₂, as they are reduced by the H₂O₂ scavenger catalase. We now propose to examine whether the changes are secondary to H₂O₂-induced impairment of releasable Ca²⁺ stores.

Methods: Normal human sigmoid colon was obtained from cancer free margins of surgical specimens, and compared to specimens obtained from UC patients. Normal muscle strips were pre-incubated in IL-1b [100 u/ml], with or without the H₂O₂ scavenger catalase or exposed to H₂O₂ (2.5-70 mmol). The strips were then digested to obtain single cells. Cell lengths were measured under contrast phase microscope and compared to non-stimulated cells to obtain cell shortening. Quantitative calcium changes were analyzed using the immuno-florescent dye Fura 2AM and a dual excitation imaging system.

Results: We have previously shown that the NKA- and thapsigargin-induced contraction of colonic muscle is mediated by release of Ca²⁺ from intracellular stores. In muscle cells from UC specimens, maximum shortening in response to NKA and thapsigargin was reduced by 45±6% and 43±4% respectively. Incubation in IL-1b reduced NKA-induced shortening by 47% (p<.001) and thapsigargin-induced shortening by 45% (p<.001). These changes were significantly inhibited by catalase (p<.05). Similarly H₂O₂ (35 mmol) reduced NKA-induced shortening of normal cells by 46%. NKA caused a 320 hmol cytosolic Ca²⁺ increase in normal cells vs. 230 hmol in UC cells. H₂0₂ exposure reduced the NKA-induced Ca²⁺ response to 90 hmol. IL-1b exposure reduced the NKA-induced Ca²⁺ response to 44 hmol which was partially reversed by catalase returning to 153 hmol.

Conclusions: The data show that H₂O₂ reduces NKA-induced contraction and Ca²⁺ release. Similiar changes induced by IL-1b depend on IL-1b-induced production of H₂O₂, as they are inhibited by the H₂O₂ scavenger catalase. The changes induced by IL-1b and H₂O₂ are similiar to those observed in ulcerative colitis, supporting the hypothesis that they may depend on the formation of reactive oxygen species.