SLC26A3 (DRA) is stimulated in a synergistic, intracellular Ca2+ dependent manner by cAMP and ATP in intestinal epithelial cells

In polarized intestinal epithelial cells, DRA is an apical Cl-/HCO3 - exchanger that is part of neutral NaCl absorption under baseline conditions but in cAMP driven diarrheas it is stimulated and contributes to increased anion secretion. To further understand regulation of DRA in conditions mimicking some diarrheal diseases, Caco-2/BBE cells were exposed to forskolin (FSK) and ATP. FSK and ATP stimulated DRA in a concentration dependent manner, ATP acting via P2Y1 receptors. FSK at 1µM and ATP at 0.25 µM had minimal to no effect on DRA given individually; however, together, they stimulated DRA to levels seen with maximum concentrations of FSK and ATP alone. In Caco-2/BBE cells expressing the Ca2+ indicator GCaMP6s, ATP increased Ca2+ in a concentration dependent manner, while FSK (1 µM), that by itself did not significantly alter Ca2+, followed by 0.25 µM ATP produced a large increase in Ca2+ that was ~equal to the elevation caused by 1 µM ATP. BAPTA-AM pretreatment prevented the ATP and FSK/ATP synergistic increased DRA activity and the increase in Ca2+i caused by FSK/ATP. FSK/ATP synergistic stimulation of DRA was similarly observed in human colonoids. Conclusion: In Caco-2/BBE cells, subthreshold concentrations of FSK (cAMP) and ATP (Ca2+) synergistically increased Ca2+i and stimulated DRA activity with both being blocked by BAPTA-AM pretreatment. Diarrheal diseases such as bile acid diarrhea, in which both cAMP and Ca2+ are elevated, are likely to be associated with stimulated DRA activity contributing to increased anion secretion, while separation of DRA from NHE3 contributes to reduced NaCl absorption.

 

Comments:

The passage describes a study conducted on Caco-2/BBE cells to investigate the regulation of the apical Cl-/HCO3- exchanger DRA in conditions mimicking some diarrheal diseases. The study found that subthreshold concentrations of forskolin (FSK) and ATP synergistically increased intracellular Ca2+ levels (Ca2+i) and stimulated DRA activity in the cells, which could contribute to increased anion secretion in diarrheal diseases with elevated cAMP and Ca2+ levels. The study also found that BAPTA-AM pretreatment blocked the synergistic effects of FSK and ATP on DRA activity and Ca2+i.

The study's findings suggest that the regulation of DRA in intestinal epithelial cells is complex and involves the interaction of multiple signaling pathways. Furthermore, the study suggests that the synergistic effects of cAMP and Ca2+ on DRA activity may play a role in diarrheal diseases associated with elevated levels of both signaling molecules.

Overall, the study provides insights into the molecular mechanisms underlying the regulation of intestinal ion transport and may have implications for the development of new treatments for diarrheal diseases.

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