Short chain fatty acids as metabolic regulators of ion absorption in the colon.

Between 50%-80% of sodium absorption in the colonic mucosa is dependent upon CO2 generation from SCFAs derived from the colonic lumen. Lumenal starvation leading to diminished SCFAs levels in the colon greatly reduce the absorptive capacity of the colonic mucosa. Mechanisms whereby SCFAs regulate sodium absorption in the colon include 1) an enzyme induced adaptive regulation of SCFA-oxidation in colonocytes, 2) a flexible CO2 supply from SCFA depending upon stimulation or suppression of fatty acid oxidation., 3) the variable sidedness of Na(+)-H+ and Cl(-)-HCO3- exchange pumps in colonic epithelial cells, and 4) colonic epithelial cell membrane synthesis from SCFAs. Precise details of these regulatory mechanisms need to be elucidated by further experimental investigation.