gamma-Glutamyl transferase activity in the pig proximal colon during early postnatal development

Binding of triiodothyronine by fully differentiated rat enterocytes

The cellular binding characteristics of triiodothyronine (T3) have been measured in a preparation of isolated fully differentiated enterocytes prepared from thyroidectomized rats. Specific binding of [125I]T3, defined as that portion displaced by the presence of 20 microM-non-radioactive hormone, was shown to become maximal after 100 min incubation with cells at a temperature of 15 degrees C. The cellular release of lactic dehydrogenase measured under these conditions was found to be 18%. Thin layer chromatography of radioactive compounds recovered from enterocytes and from incubation medium showed less than 2% radioactivity to be as free iodide. The amount of [125I]T3 specifically bound to enterocytes showed a curvilinear dependence on the concentration of T3 present in the incubation medium. Scatchard plot analysis of this data revealed the presence of both high (KD 1.2 +/- 1.1 X 10(-9) M) and low (KD 1.9 +/- 0.8 X 10(-7) M) affinity binding sites in these cells. Previous injection of non-radioactive T3 into thyroidectomized rats, at a time chosen to ensure negligible levels of circulating T3 at the time of the experiment, caused a 3-fold reduction in the maximal binding capacity of the low-affinity site (83 compared with 28 pmol/mg protein). Neither the affinity nor the number of high-affinity binding sites for T3 were significantly affected by this treatment. These results are compared with those obtained using other types of cell responsive to T3. The possible physiological importance of these findings is discussed.

Postnatal development of gamma-GT activity in rat brain microvessels corresponds to capillary growth and differentiation

It has been demonstrated histochemically that endothelial cells of the cerebral capillaries show a high activity in gamma-glutamyl transpeptidase (gamma-GT), an enzyme which takes part in the transfer of large neutral amino acids across the blood-brain barrier. Reports of the disappearance of enzyme activity in endothelial cells (EC) grown in culture suggest that the presence of astroglial cells (AG) is required for the expression of gamma-GT in these cells. The present study deals with the developmental changes in gamma-GT activity in capillaries of rat cerebral cortex during ontogenesis (i.e. on days 2, 7, 11, 14, 21 and 60 after birth). gamma-GT activity is determined by measuring the enzyme kinetics of the histochemical reaction on isolated brain capillaries using a flying spot microscope densitometer. Enzyme activity is expressed as an increase in relative optical density (at 500 nm) in arbitrary units/min/micron 2 during the 2 min immediately after initiating incubation and corresponds to the gamma-GT active area (in micron 2) of the capillary segment. During early postnatal development, a biphasic change of gamma-GT activity in capillaries of rat cerebral cortex is observed. The first phase (i.e. the postnatal period between the 2nd and 12th day) is characterized by a significant decrease in gamma-GT activity, which coincides with the onset of the rapid mitotic proliferation of cortical endothelial cells. During the second phase (i.e. the postnatal period between the 12th and 21st day), a fast increase in the gamma-GT activity can be measured. Then enzyme activity reaches the adult level between the 21st and 60th postnatal day.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of carbonic anhydrase activity in the developing rat colon

Carbonic anhydrase activity was localized histochemically by light and electron microscopy in the proximal and distal colon of developing rats. Fixed tissue was taken for normal morphology and carbonic anhydrase localization from fetal (20-22 days gestation), suckling (1-19 days postnatal), weanling (20-25 days postnatal), and adult rats. The proximal colon had distinct villi at birth which were diminished between days 5 and 11 postnatally. The distal colon lacked villi at birth but had rudimentary crypts (ridges and furrows) which were replaced during the suckling period by a flat mucosa interspersed with true crypts. Carbonic anhydrase first appeared in both proximal and distal colonic epithelial cells on the day of birth (22 days gestation). Goblet cells were nonreactive at each developmental period. In neonatal rats, epithelial cells in the upper half of the villi of the proximal colon and on the surface and upper crypts of the distal colon were positive for carbonic anhydrase throughout the cytoplasm. Cells at the villar base (proximal colon) or in the deep crypt (distal colon) had reaction product in the intercellular spaces but not the cytoplasm. By 11 days postnatal, cytoplasmic reaction product was present in proximal colonic cells in the upper three-fourths of the crypt and was concentrated in a heavy band in the apical cytoplasm. In the distal colon, cytoplasmic positive cells did not extend as deeply into the crypts and the apical banding pattern was weak. Intercellular spaces in the deeper crypt epithelium were positive in both proximal colon and distal colon, suggesting a membrane-bound carbonic anhydrase. It was concluded that carbonic anhydrase appeared suddenly at birth and was continuously present in mid- to upper-crypt (or upper villus in early neonatal proximal colon) non-goblet cells into adulthood. This suggests a functional role for carbonic anhydrase in chloride-bicarbonate exchange across the neonatal and adult colonic mucosa.

A rabbit jejunal isolated enterocyte preparation suitable for transport studies

A method is described for isolating viable enterocytes from rabbit jejunum. Estimates of sucrase and gamma-glutamyl transferase activities in cells isolated by this method suggest that they originate from the upper villus only. Isolated cells accumulate both alpha-methyl-D-glucoside and alanine, maintaining high intracellular concentrations for at least 60 and 40 min respectively. Accumulation of alpha-methyl-D-glucoside is inhibited by the presence of phloridzin. The cells accumulate 42K and 86Rb in an identical manner. This uptake, which is maintained for at least 60 min, is inhibited in the presence of ouabain. Passive efflux of 42K and 86Rb occurs with rate constants which are virtually identical. The efflux follows a single exponential suggesting that it originates from only one intracellular compartment. It is suggested that the preparation can be used to study the effect of sugars and amino acids on K efflux. The advantages of using such a preparation are discussed.

The distribution of (Na+ + K+)-ATPase along the villus crypt-axis in the rabbit small intestine

The migration of intestinal epithelial cells from the crypts to the tips of villi is associated with progressive cell differentiation. The changes in Na+-pump levels during migration have been measured in epithelial cells isolated from rabbit small intestine. A significant proportion of ouabain-sensitive (Na+ + K+)-ATPase in the cell homogenates was latent but could be unmasked by detergent treatment. Highest detergent activation was observed in villus cells. The distribution of pumping sites was also assessed by measuring ouabain binding to intact cells. The kinetics of specific binding was consistent with the interaction of the cardiac glycoside with a single population of binding sites with an apparent Kd of around 10(-7) M. Both enzyme assay and ouabain-binding measurements suggest that a 2-3-fold increase in the number of Na+-pumping sites accompanies cell differentiation in rabbit jejunal epithelium. This increase in pumping capacity might be an adaptation of the cells to their absorptive function.

The development of gamma-glutamyltransferase in a pig renal-epithelial-cell line in vitro. Relationship to amino acid transport

The pig kidney-cell line, LLC-PK1, possesses gamma-glutamyltransferase with properties similar to those of the purified renal enzyme. gamma-Glutamyltransferase activity increases after cells are seeded at low density to reach values comparable with those found in kidney cortex when the cells are fully confluent. This increase is paralleled by an increase in alpha-methyl D-glucoside uptake. In contrast, the uptakes of L-leucine and L-alanine decrease during this time. These results suggest that gamma-glutamyltransferase is not important as a mediator of the renal transport of neutral amino acids.