Bicarbonate secretion and acid/base sensing by the intestine.

The transport of bicarbonate across the enterocyte cell membrane regulates the intracellular as well as the luminal pH and is an essential part of directional fluid movement in the gut. Since the first description of "active" transport of HCO₃^- ions against a concentration gradient in the 1970s, the fundamental role of HCO₃^- transport for multiple intestinal functions has been recognized. The ion transport proteins have been identified and molecularly characterized, and knockout mouse models have given insight into their individual role in a variety of functions. This review describes the progress made in the last decade regarding novel techniques and new findings in the molecular regulation of intestinal HCO₃^- transport in the different segments of the gut. We discuss human diseases with defects in intestinal HCO₃^- secretion and potential treatment strategies to increase luminal alkalinity. In the last part of the review, the cellular and organismal mechanisms for acid/base sensing in the intestinal tract are highlighted.