NUTRIENT OXIDATION BY RAT INTESTINAL EPITHELIAL-CELLS IS CONCENTRATION-DEPENDENT

The kinetics of oxidative metabolism of glucose, glutamine, acetate an d butyrate were determined in cells isolated from the jejunum and colo n of young, fed rats. Jejunal and colonic cells were isolated from the same animal and incubated with a single radiolabeled substrate at con centrations ranging from 0.005 to 25 mmol/L, and (CO2)-C-14 Production was determined. Carbon dioxide production was concentration dependent and saturable for all substrates. Data points within the range of the apparent half-maximal oxidation rate were transformed by use of a Lin eweaver-Burk plot to calculate K(ox), the concentration at which there was half-maximal oxidation, and V(max), the calculated maximal rate o f oxidation. In jejunal cells, the K(ox) for glucose and glutamine wer e 0.40 and 0.45 mmol/L, respectively. The K(ox) for glucose, glutamine and acetate ranged from 0.80 to 0.88 mmol/L in colonocytes, whereas t he K(ox) for butyrate was 0.33 mmol/L. Except for butyrate in colonocy tes, the observed maximal rate of oxidation was comparable to the calc ulated maximal rate. The substrate concentration required to ensure th at substrate was not limiting for its oxidation was estimated at 5 mmo l/L for glucose and glutamine in enterocytes and colonocytes, 5 mmol/L for acetate in colonocyles, and 0.50 mmol/L for butyrate in colonocyt es. This study showed that attention needs to be given to the concentr ation of substrate used for in vitro studies.