Chemoprotective nutrients modulate intracellular calcium compartmentalization and store‐operated channel entry to induce colonocyte apoptosis

Butyrate, a fermentable fiber metabolite, enhances the chemoprotective, proapoptotic effects of docosahexaenoic acid (DHA) in the colon. Since mobilization of Ca 2+ from the endoplasmic reticulum and mitochondria are known to activate apoptosis, we hypothesized that DHA and butyrate promote apoptosis by altering Ca 2+ flux. Mouse colonocytes were treated with 50 μM DHA or linoleic acid (LA) for 72 h ± butyrate (0–10 mM) for the final 24 h. Fluorescent indicators, Fluo‐4 and Rhod‐2 were used to measure changes in cytosolic and mitochondrial Ca 2+ . Thapsigargin was used to determine IP 3 Ca 2+ pool and store‐operated channel (SOC)‐mediated changes. DHA and butyrate did not alter basal Ca 2+ or the IP 3 pool with 6 h butyrate co‐treatment. In contrast, at 12 and 24 h, DHA and butyrate cultures exhibited a 25 and 38% decrease in cytosolic Ca 2+ compared to LA and butyrate. Extracellular Ca 2+ chelation with EGTA abolished the effect of Thapsigargin on the IP 3 ‐releasable Ca 2+ pool. Addition of Ca 2+ to the media reestablished the difference in Ca 2+ entry between the two groups. Consistent with this finding, DHA and butyrate increased the ratio of mitochondrial to cytosolic Ca 2+ at 12 and 24 h by 25 and 36%, respectively. These data demonstrate that DHA and butyrate combination uniquely modulate intracellular Ca 2+ homeostasis by altering cytosolic and mitochondrial Ca 2+ flux through an SOC‐mediated mechanism. Supported by NIH CA59034 and P30ES09106.