Acetate, butyrate and proline uptake in the caecum and colon of prairie voles (Microtus ochrogaster)

We have measured unidirectional uptake (not transmural flux) of acetate, butyrate and proline by everted sleeves of intact tissue from the jejunum, caecum, proximal colon and distal colon of prairie voles (Microtus ochrogaster). There was active (i.e. Na(+)-dependent) transport of L-proline in the jejunum, but we found no evidence for it in any region of the hindgut (i.e. the caecum, proximal colon and distal colon). Uptake of acetate was carrier-mediated in all three regions of the hindgut, but the Jmax and apparent Km (< or = 1.5 mmol l-1) were low, and uptake was primarily passive over the concentration range 10-50 mmol l-1, which spanned measured acetate levels in the caecum and proximal colon. At 100 mmol l-1, acetate uptake (nmol min-1 cm-2) was higher (P < 0.001) in distal colon (359 +/- 33) than in the proximal colon (225 +/- 17) and caecum (150 +/- 5) (mean +/- S.E., N = 8). Uptakes summed over the length of each region were also higher (P < 0.001) in the distal colon at 100 mmol l-1, but not at low concentrations (0.1 mmol l-1). Uptakes normalized to diffusion coefficients were higher for butyrate than acetate and were lowest for L-glucose (which is absorbed passively via an aqueous pathway) in all regions, indicating that uptake of the short-chain fatty acids involves solubilization in the lipid bilayer of the apical membrane. The short-chain fatty acids absorbed from the hindgut of the vole were equivalent to 22% of standard metabolic rate or 15% of resting (but fed) metabolic rate.