Ce. Kight et Se. Fleming, NUTRIENT OXIDATION BY RAT INTESTINAL EPITHELIAL-CELLS IS CONCENTRATION-DEPENDENT, The Journal of nutrition, 123(5), 1993, pp. 876-882
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.