Colonic absorption of inorganic ions and volatile fatty acids in the rabbit.

Net fluxes of water, Na+, K+, Cl-, HCO3- and volatile fatty acids (VFA) were investigated in three different segments of rabbit colon. Two opposite phenomena occurred: secretion of water and inorganic ions in the oral part of the colon and absorption in the remaining colon; VFA were always absorbed. The movement of cations was closely correlated with those of VFA and Cl-. Results are consistent with the presence of exchange: Na+/H+, K+/H+, in the colon brush border membrane. In fact net absorption of cations and VFA seems linked to the availability of protons. In the absence of net cation transport an additional source of protons may be provided by hydration of luminal CO2. So VFA could enter mucosa by passive diffusion as the undissociated acids.