Isolation and metabolic characteristics of rat and chicken enterocytes

Abstract

1. The recent recognition of the metabolic, as opposed to absorptive, functions of the small intestine prompted efforts the improve the preparation of metabolically competent columnar absorptive cells ('enterocytes') and to study their metabolic properties. 2. With this preparation, linear rates of O2 consumption are obtained for 40 min at 37 degrees C that are more than 50% higher than rates reported by other authors. 3. Among added substrates, glucose, glutamine and glutamate are the preferred fuels of respiration. The main nitrogenous products of glutamine metabolism are NH3, alanine and glutamate. Glutamine carbon was not detectable in citrulline or proline, in contrast with the findings of Windmueller & Spaeth [(1974) J. Biol. Chem. 249, 5070-5079] in the vascularly perfused small intestine. 4. The rates of O2 uptake in the presence of glutamine or glutamate are sufficient to account for the formation of the carbon skeleton of alanine from the amino acid substrate, i.e. the ratio of O2 used/alanine formed is greater than 1.5. 5. Added ADP and ATP are rapidly degraded to AMP and IMP to a large extent by release of hydrolytic enzymes from the enterocytes into the medium. 6. Chicken enterocytes isolated by the same method are more stable; linear rates of O2 uptake are maintained for 60-70 min.

Fuel utilization in colonocytes of the rat

“…The ATP/AMP concentration ratio decreased considerably after 30 min of incubation. This is in contrast with the situation found in rat enterocytes, in which a more rapid decrease in ATP/AMP concentration ratio was observed (Watford et al, 1979), but similar to that in rat lymphocytes for the same period of incubation (see Ardawi & Newsholme, 1983a). These results, together with the fact that rates of 02, glucose or glutamine utilization, and of lactate or glutamate production, were linear over 30 min (results not shown), indicate that isolated incubated rat colonocytes provide a satisfactory viable system for short-term metabolic studies (i.e.…”

“…Glutamine, n-butyrate or ketone bodies were the only.substrates that increased the rate of 02 consumption (Table 1). The respiratory stimulation by n-butyrate contrasts with that observed in isolated enterocytes (Watford et al, 1979).…”

“…However, the oxidation of fatty acids did not contribute significantly to energy formation even in the starved state (Hanson & Parsons, 1977Windmueller &Spaeth, 1978Watford et al, 1979;Windmueller, 1984). In a similar manner to other rapidly dividing cells (e.g.…”

“…All spectrophotometric measurements were performed in a Gilford recording spectrophotometer (model 240) at 25°C, except for glucose-6-phosphatase and glutaminase, which were determined at 30 and 37°C respectively. For all enzymes studied, preliminary experiments established that extraction and assay procedures were such as to provide maximum enzyme activities (see Crabtree et al, 1979 (Roediger & Truelove, 1979;Roediger, 1982), but higher than that reported for human colonocytes (Roediger & Truelove, 1979), rat lymphocytes (Ardawi & Newsholme, 1983a) or rat thymocytes (Hume et al, 1978), and similar to that observed in rat enterocytes (Watford et al, 1979;Porteous, 1980). Glutamine, n-butyrate or ketone bodies were the only.substrates that increased the rate of 02 consumption (Table 1).…”

“…In a similar manner to other rapidly dividing cells (e.g. lymphocytes, thymocytes, tumour cells), these epithelial cells are also characterized by a high rate of glycolysis in either the fed or the starved state (Watford et al, 1979;Hume et al, 1978;Ardawi & Newsholme, 1983a). Experiments with incubated lymphocytes suggested that most of the energy requirements in either the fed or the starved state were provided from the utilization of fatty acids, glutamine and glucose, whereas ketone bodies appeared to be much less important (Ardawi & Newsholme, 1982, 1983a,b, 1984a,b, 1985.…”