Antipili antibody affords protection against ascending pyelonephritis in rat: evaluated by renal brush border membrane enzymes

Kinetic parameters (Km and Vmax) of renal brush border membrane (BBM) enzymes alkaline phosphatase, maltase, leucine aminopeptidase and gamma-glutamyltranspeptidase were worked out in control, infected and immunized-infected rats. There was no significant change in the Km of all the enzymes studied in three groups. The Vmax of all the enzymes studied decreased significantly (p less than 0.05) 3 or 4 days postinfection and onwards in the left obstructed kidney of infected and immunised-infected animals. However, in the right unobstructed kidney the Vmax of alkaline phosphatase and leucine aminopeptidase increased significantly (p less than 0.05) in the early stages and decreased (p less than 0.05) in later stages in both the experimental groups. The significant difference (p less than 0.05) in the Vmax of infected and immunized-infected groups at various stages of infection revealed the partial protective role of antipili antibody against ascending pyelonephritis.     

Renal nutrients uptake and brush-border membrane enzymes in cholesterol-fed guinea pigs

The effect of dietary cholesterol load on the reabsorption of nutrients and the enzyme and chemical characteristics of renal brush-border membrane (BBM) was evaluated in guinea pigs. The transport of D-glucose and amino acids into the renal BBM vesicles of experimental animals was significantly (P less than 0.001) decreased. Vmax of leucine aminopeptidase decreased without alteration in Km; however, both the Km and Vmax of alkaline phosphatase and maltase decreased in renal membrane in response to cholesterol load. The alterations in the chemical architecture of the membrane could possibly be responsible for the observed aberrations in the kidneys of cholesterol-fed animals.     

Effects on intestinal nutrient uptake and brush border membrane enzymes in response to atherogenic diet in rhesus monkeys

Transport of nutrients and kinetic parameters (Vmax and Km) of brush border membrane (BBM) enzymes were studied in duodenum, jejunum, and ileum from atherogenic diet-fed monkeys. The Km remained unaltered while feeding of atherogenic diet resulted in higher Vmax of sucrase, maltase, and alkaline phosphatase and lower Vmax of gamma-glutamyltranspeptidase and leucine-aminopeptidase compared to controls. Na+-dependent D-glucose transport was higher in duodenum and jejunum and unaltered in ileum. In contrast to D-glucose transport, the transport of amino acids was decreased in all three intestinal segments from atherogenic diet-fed monkeys.     

Effect of heat-stable and heat-labile enterotoxins of Escherichia coli on intestinal brush border membrane enzymes of mice

The activities of intestinal brush border membrane (BBM) enzymes alkaline phosphatase, maltase, lactase, sucrase, gamma-glutamyl transpeptidase and leucine aminopeptidase were determined in intestinal homogenates and purified BBMs from control, heat-stable and heat-labile enterotoxin treated mice. The activities of all the enzymes except lactase were decreased significantly (p less than 0.01) in homogenates while increased significantly (p less than 0.001) in BBMs of experimental groups as compared to controls. Calmodulin activities were increased significantly (p less than 0.01) as compared to control in heat-stable enterotoxin treated mice but remained unaltered in heat-labile enterotoxin treated mice. DNA contents of intestinal homogenates were decreased in experimental groups demonstrating the decrease in cell number in these groups. The altered BBM enzyme activities could not be attributed to changes in calmodulin activities. The increase in enzyme activities in BBMs may reflect a compensatory phenomenon in the remaining cells.     

Kinetics of reabsorption of nutrients in renal brush border membrane vesicles from rats with experimental ascending pyelonephritis

The uptake of nutrients was investigated in the renal cortical brush border membrane (BBM) vesicles at different stages of ascending pyelonephritis. There was significant difference (p less than 0.05) in the uptake of D-glucose, L-alanine, L-aspartate, L-lysine and L-proline 3 days postinfection and onwards in both right unobstructed and left obstructed experimental kidneys as compared to the sham operated control. The uptake of D-glucose, L-lysine and L-proline was found to be significantly decreased (p less than 0.05) during the course of infection. While uptake of L-alanine and L-aspartate increased (p less than 0.05) in early stages and decreased (p less than 0.05) in later stages of infection. The differential effect was attributed to the compensatory measure and different kinds of transport systems for different types of amino acids.     

Transport of nutrients into the renal brush border membrane vesicles as marker in evaluating the role of antipili antibodies in modulation of ascending pyelonephritis in rats

The uptake of D-glucose, L-aspartate, L-lysine and L-proline was investigated in renal brush border membrane (BBM) vesicles prepared from control, infected or passively-immunized-infected rats. Except L-aspartate, a progressive decrease in the uptake of these nutrients in both infected and immunized-infected groups during the course of infection was observed, but the changes were less apparent in immunized-infected rats than in non-immunized ones. The uptake of L-aspartate was increased in vesicles from early stages of infection but decreased in those from later stages. Also in L-aspartate uptake, the changes were smaller in immunized animals. The uptake of nutrients was detectable earlier than were histopathological alterations of both kidneys. The observations demonstrated that uptake of D-glucose and amino acids in the kidneys is disturbed prior to appearance of histopathological lesions and thus can be used for early detection of the disease. The data also demonstrate that antipili antibodies afford partial protection against ascending pyelonephritis.     

Influence of age on duodenal brush border membrane and specific activities of brush border membrane enzymes in Wistar rats.

To examine age-related changes in the morphology of intestinal brush border membrane (BBM; microvilli) and specific activities of intestinal BBM enzymes including alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (gamma-GT), and disacchridase, four groups of Wistar rats were sacrificed at 2.5 wk, 5 wk, 5 mon and 23 mon. In an electron microscopic examination, morphologically a less dense BBM structure in the duodenum of rats aged 23 mon was observed than that of rats aged 5 mon. Specific activity of ALP in the duodenum from 5-mon-old rats was significantly higher than from rats aged 2.5 wk and 23 mon. The mucosal tissues from 5-wk-old rats had significantly higher specific activity of gamma-GT than did tissues from the other ages. In sucrase and maltase specific activities, 5-mon-old rats had higher activities of these enzymes than other age groups, especially 2.5-wk- and 23-mon-old rats. There was also a significant effect of site on intestinal BBM enzyme activities in post-weanling rats. Regional gradients of ALP and gamma-GT along the entire small intestine (duodenum > jejunum > ileum) were remarkable. Disaccharidase activities peaked in the jejunum and declined toward both the duodenum and ileum. Taken together the result obtained here suggested that 5-mon-old rats had the most elevated intestinal function. This result also strongly indicated that the structure of the intestinal BBM and development of intestinal BBM enzymes in Wistar rate were markedly influenced by age during the postnatal period.     

Ectopic expression of alkaline phosphatase in proximal tubular brush border membrane of human renal cell carcinoma

The present study was conducted to find out any alteration in the expression and activity of alkaline phosphatase in the brush border membrane (BBM) from renal cell carcinoma (RCC) in comparison to normal renal BBM. The specific activity of alkaline phosphatase was drastically reduced in homogenate as well as BBM from RCC kidney when compared to ALP activity in BBM of normal kidney. Kinetic studies revealed that diminished activity of alkaline phosphatase in BBM isolated from RCC was fraternized with decrease in maximal velocity (V(max)) and increase in affinity constant (K(m)) of the enzyme. SDS-PAGE studies showed that the BBM proteins having molecular weights ranging from 95 to 170 kDa were poorly expressed in RCC BBM in relative to normal kidney BBM. Incubation of SDS-PAGE gel with BCIP/NBT dye clearly showed that the expression of ALP in tumor renal BBM was markedly reduced as compared to normal kidney. Further, Western blot analysis using anti-alkaline phosphatase antibody also confirmed the reduced expression of ALP in tumor renal BBM. Lipid composition in reference to phospholipids, glycolipids and cholesterol in tumor renal BBM was altered to that of normal renal BBM, indicating alteration in membrane fluidity of tumor renal BBM.     

Induction of microvillar hydrolase activities by cell density and exogenous differentiation inducers in an established kidney epithelial cell line (LLC-PK1)

Several hydrolase activities characteristic of the apical brush border membrane of renal proximal tubule, leucine aminopeptidase, gamma-glutamyl transpeptidase, alkaline phosphatase, maltase, and trehalase, were identified in cultures of the LLC-PK1 kidney epithelial cell line. A coordinate increase in activities of these enzymes was observed upon development of a confluent cell density and functional membrane polarization. Further large progressive increases in individual hydrolase activities were induced after the addition of compounds known as differentiation inducers. Hexamethylene bisacetamide preferentially induced increased trehalase and maltase activities. Induced trehalase activity exhibited an increased Vmax but a similar Km compared with activity in control extracts. Induction required protein synthesis and was dependent on inducer concentration and exposure time. Treatment of confluent cultures with N,N'-dimethylformamide triggered an induction of maltase, trehalase, alkaline phosphatase, and gamma-glutamyl transpeptidase activities, whereas dimethylsulfoxide induced trehalase and gamma-glutamyl transpeptidase activities. Increased leucine aminopeptidase and maltase activities were observed after addition of the phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine. Induction of trehalase activity by N,N'-dimethylformamide was reversible over a 4-day period after removal of inducer, but effects of hexamethylene bisacetamide were irreversible. These results suggest that the LLC-PK1 cell line reproducibly develops differentiation-specific characteristics under defined conditions in cell culture, which can be individually modulated by chemicals known as inducers of cell differentiation.     

Increased Na(+)-dependent D-glucose transport and altered lipid composition in renal cortical brush-border membrane vesicles from bile duct-ligated rats.

Erythrocyte membranes of patients with liver disease are characteristically enriched in cholesterol, a change known to impair several carrier-mediated membrane transport functions. In the present study we have assessed whether experimental liver disease can affect the membrane lipid composition and transport function of kidney epithelial cells. Small (about 5%) but significant (P less than 0.01) increases were found in the cholesterol-to-phospholipid molar ratio (C/PL) of rat renal cortical brush-border membrane (BBM) vesicles 3, 8, and 15 days after bile duct ligation which correlated closely with increased fluorescence polarization, i.e., decreased membrane fluidity (r = 0.75, P less than 0.001; n = 27). A lipoprotein-mediated pathogenesis was suggested by the close relationship between BBM C/PL and plasma C/PL (r = 0.69, P less than 0.001). The mean high-affinity Na(+)-coupled D-glucose uptake by BBM vesicles was higher 1, 3, 8, and 15 days after ligation than in non-operated rats, significantly so at 3 and 8 days (611 +/- 37 and 593 +/- 22 vs. 507 +/- 21 pmol/mg protein per 4 sec; P less than 0.05), and was positively correlated with BBM C/PL (r = 0.58, P less than 0.01) and fluorescence polarization (r = 0.41, P less than 0.05). Brief incubation of BBM vesicles from normal rats with cholesterol-rich phospholipid liposomes simultaneously increased BBM C/PL and Na(+)-dependent D-glucose uptake. Stimulation of BBM Na(+)-glucose cotransport in ligated rats was not due to delayed dissipation of the Na+ gradient or to a more rapid development of membrane potential. High-affinity Na(+)-dependent D-glucose uptake kinetics in 3-day bile duct-ligated rats showed a lower Kt, without an alteration in maximum velocity, Vmax, compared to sham-operated animals (0.298 +/- 0.015 vs. 0.382 +/- 0.029 mM; P less than 0.05), whilst the binding dissociation constant, Kd of high-affinity phlorizin binding sites was reduced by ligation (0.453 +/- 0.013 vs. 0.560 +/- 0.015 microM; P less than 0.001). We conclude that an early effect of bile duct ligation is to enrich renal cortical brush-border membranes in cholesterol, thereby decreasing membrane fluidity and stimulating Na(+)-dependent D-glucose uptake by increasing the affinity of the carrier.     

Role of N-linked oligosaccharides in the transport activity of the Na+/H+ antiporter in rat renal brush-border membrane

The role of N-linked oligosaccharide side chains in the biogenesis and function of Na+-coupled transporters in renal luminal brush-border membrane (BBM) is not known. We examined the question of how in vivo inhibition by alkaloid swainsonine of alpha-mannosidase, a key enzyme in processing of glycoproteins in the Golgi apparatus, affects Na+/H+ antiport and Na+/Pi symport as well as activities of other transporters and enzymes in rat renal BBM. Administration of swainsonine to thyroparathyroidectomized rats, control or treated with 3,5,3'-triiodothyronine, markedly decreased the rate of Na+/H+ antiport, but had no effect on the rate of Na+/Pi symport across renal BBM vesicles (BBMV). Moreover, administration of swainsonine did not change activities of Na+ gradient, ([extravesicular Na+] greater than [intravesicular Na+])-dependent transport of D-glucose, L-proline, or the amiloride-insensitive 22Na+ uptake by BBMV; the activities of the BBM enzymes alkaline phosphatase, gamma-glutamyltransferase, or leucine aminopeptidase in BBMV were also not changed. The in vitro enzymatic deglycosylation of BBM by incubating freshly isolated BBMV with bacterial endoglycosidase F also resulted in a decreased rate of Na+/H+ antiport, but not Na+-coupled symports of Pi, L-proline, and D-glucose, or the activities of the BBM enzymes were not significantly affected. Similar incubation with endoglycosidase H was without effect on any of these parameters. Both the modification of BBMV glycoproteins by administration fo swainsonine in vivo as well as the in vitro incubation of BBMV with endoglycosidase F resulted in a decrease of the apparent Vmax of Na+/H+ antiport, but did not change the apparent Km of this antiporter for extravesicular Na+ and did not increase H+ conductance of BBM. Taken together, our findings suggest that intact N-linked oligosaccharide chains of the biantennary complex type in renal BBM glycoproteins are required, directly or indirectly, for the transport function of the Na+/H+ antiporter inserted into BBM of renal proximal tubules.     

Diets alter jejunal morphology and brush border membrane composition in streptozotocin-diabetic rats

Previous studies have demonstrated enhanced active and passive uptake of many nutrients in animals with experimental diabetes. These changes in absorption cannot be explained by differences in intestinal morphology, although the brush border membrane (BBM) phospholipids do change in diabetes. Manipulation of diet produces alterations in intestinal uptake of lipids and glucose. This study was undertaken to determine the effect of diet and diabetes on jejunal morphology and BBM lipid composition. Rats were rendered hyperglycemic with streptozotocin and were fed for 2 weeks on a diet that was high or low in carbohydrate, essential fatty acids, cholesterol, or protein. In both control and diabetic rats, these diets produced changes in villus height and BBM sucrase and alkaline phosphatase activities. In both control and diabetic rats, BBM phospholipids were unaffected by changes in the dietary content of essential fatty acids, cholesterol, or protein, but total BBM phospholipid content was reduced in animals fed low as compared with high carbohydrate diet. Total BBM phospholipid content was higher in diabetic than in control animals fed the low protein diet, whereas BBM phospholipid content was lower in diabetic than in control animals fed the high carbohydrate diet, and was even lower in diabetic animals fed the low as compared with the high carbohydrate diet. These changes in total phospholipids were due to alterations in the BBM content of phospholipids containing choline. In control animals, BBM cholesterol was higher in rats fed the low as compared with the high cholesterol diet, or the low as compared with the high protein diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular basis of renal handling of calcium in response to thyroid hormone status of rat

We investigated the effect of thyroid hormone status on renal handing of Ca2+. Further, like kinetics of Ca2+ transport across brush-border membrane (BBM) and basolateral membrane (BLM) of renal epithelial cells was carried out. FE(Ca) was decreased in hyperthyroid (Hyper-T) rats and increased in hypothyroid (Hypo-T) rats as compared to euthyroid (Eu-T) rats. Ca2+ uptake into renal brush-border membrane vesicles (BBMV) was increased in Hyper-T rats and decreased in Hypo-T rats as compared to Eu-T rats. K(m) was lower in Hyper-T rats and higher in Hypo-T rats as compared to Eu-T rats whereas, V(max) remained unaltered. The transition temperature for calcium uptake varied inversely with the thyroid hormone status. Renal BBM of Hyper-T rats showed decreased anisotropy and polarisation of DPH as compared to EU-T rats whereas these values were increased in Hypo-T rats. Thus, the altered BBM fluidity appears to modulate Ca2+ transport across BBM. Na+/Ca2+ exchange activity of renal cells was increased in Hyper-T and decreased in Hypo-T rats as compared to Eu-T rats. V(max) for Na+/Ca2+ exchange was increased in Hyper-T rats and deceased in Hypo-T rats as compared to Eu-T rats, whereas, [Na+](0.5) was similar in all three groups. The c-AMP levels of renal cortex of Hyper-T rats was increased and that of Hypo-T rats decreased as compared to Eu-T rats. Thus, thyroid hormones increased Ca2+ reabsorption in the kidney of rat. Thyroid hormone-mediated modulation of BBM fluidity appears to stimulate Ca2+ uptake into renal BBMV. Thyroid hormones possibly activated the Na+/Ca2+ exchanger through cAMP-dependent pathway.     

Age-related changes in enzyme activities, protein content and lipid composition of rat kidney brush-border membrane

Age-related changes in enzyme activities, protein electrophoretic patterns and lipid composition of kidney-brush-border membranes were studied in 10-20- and 30-month-old male and female Wistar rats. Polyacrylamide gel electrophoresis of membrane proteins revealed very little changes with increasing age, whether males or females were considered. The Km of three hydrolases - maltase, L-aminopeptidase and alkaline phosphatase - were not affected by age while the Vmax of maltase and alkaline phosphatase, but not of L-aminopeptidase, decreased from 10 to 30 months. The phospholipid to protein ratio which remained constant between 10 and 20 months, rose in both sexes from 20 to 30 months. In males, the cholesterol content of the membrane increased faster than that of phospholipid and the cholesterol over phospholipid ratio was then greater at 30 months than at 10 months, while in females this ratio remained unchanged in the course of aging. The fatty acid composition of the brush-border remained more or less constant with age in female rat whereas in the male, a 10% decrease in the proportion of arachidonic acid from 10 to 30 months was responsible for a lower unsaturation index.     

Intestinal brush border membrane marker enzymes, lipid composition and villus morphology: effect of fasting and diabetes mellitus in rats

Diabetes mellitus is associated with enhanced passive intestinal uptake of cholesterol and fatty acids. In order to determine the basis for these changes in intestinal permeability, the jejunal morphology and the lipid content of purified brush border membranes (BBM) were measured in fasted and fed control (C) and streptozotocin diabetic (DM) rats. There was no difference between C and DM in BBM sucrase or alkaline phosphatase; fasting had no effect on BBM enzymes in C, but in DM fasting was associated with increased sucrase activity per length of jejunum. In C fasting was associated with higher levels of BBM total phospholipid, lecithin, choline and amine phospholipids, whereas fasting in DM was associated with higher BBM cholesterol and lower free fatty acids. In the fasting DM, there was a greater villus and mucosal surface area than in the fasting C. A previous study demonstrated that with fasting in DM versus C, cholesterol uptake was unchanged, but when animals were fed, cholesterol and fatty acid uptake were greater into the jejunum of fed DM as compared with fed C. In the BBM of fed DM as compared with C, there was a significant increase in total phospholipid, lecithin, phosphatidyl ethanolamine, choline and amine phospholipids, and phospholipid/cholesterol ratio. Thus, (1) fasting is associated with changes in intestinal morphology, BBM lipids; (2) the effect of fasting is different in DM and C; (3) the enhanced uptake of lipids into the jejunum of fed diabetic rats is not due to changes in villus morphology, but may be due to alterations in the BBM phospholipids.     

Biochemical analysis of jejunal brush border membrane of golden hamster: pathogenic modulations due to ancylostomiasis.

The common hookworm (Ancylostoma ceylanicum) infection of humans was studied in golden hamsters model system. Significant biochemical modulations were observed in hamster jejunal brush border membrane (BBM), the primary site of infection. Analysis of BBM at the peak of infection (3-weeks) revealed a marked decrease in the activities of sucrase, lactase and maltase, while activities of alkaline phosphatase, (Ca2+ + Mg2+)-ATPase and gamma-glutamyl transpeptidase were increased. Kinetic studies conducted with maltase, a superficially localised enzyme of jejunal BBM, revealed loss of enzyme active site during the infection. Among other constituents, the levels of cholesterol and triglycerides were significantly decreased with slight increase in phospholipid content in the infected animals. The hookworm infection also caused a decline in total hexose content indicating an altered membrane glycocalyx. Conversely, there was significant enhancement of hydroxyproline and sialic acid contents. SDS-PAGE analysis showed an enhancement in both low and high molecular weight proteins in jejunal BBM preparations of the infected group. Gel electrophoresis of glycoproteins further revealed the appearance of two additional peaks in the low molecular weight region and concomitant disappearance of a peak in the high molecular weight region. These results strongly support the view that the hookworm infection causes severe damage not to the site of attachment alone but also to the entire cell lining of the jejunum and therefore could influence overall digestion and absorption.     

Circadian rhythms in digestive enzymes in the small intestine of rats. I. Patterns of the rhythms in various regions of the small intestine.

The activities of the digestive enzymes, maltase [EC 3.2.1.20], sucrase [EC 3.2.1.26], trehalase [EC 3.2.1.28], Leucine aminopeptidase [EC 3.4.11.1], and alkaline phosphatase [EC 3.1.3.1] were measured in various regions of the small intestine of rats. The activities of all these enzymes were much higher in the jejunum than in the ileum, and in the distal regions of the ileum no sucrase, trehalase or alkaline phosphatase activity was detected. In the jejunum, the activities of all the enzymes tested exhibited clear circadian variations with the highest activity at 0000-0400 h and the lowest at 1200 h when the rats were fed ad libitum. In the ileum, maltase and sucrase also exhibited circadian variations, but the amplitude of the rhythm was smaller than that in the jejenum. Trehalase and alkaline phosphatase did not show any circadian variation in the ileum. Leucine aminopeptidase showed a circadian variation in the ileum with the same amplitude as in the jejunum. The phase of the circadian variations shifted about half a day when the rats were fed in the daytime, but the amplitude of the rhythm did not change.     

Investigation of some characteristics of enzymes effecting the process of membrane digestion in the paddlefish <Emphasis Type="Italic">Polyodon spathula</Emphasis>

For the first time, a complex investigation of characters of some enzymes effecting the membrane hydrolysis of food in the paddlefish Polyodon spatula is made. The zone of optimum values of temperature of alkaline phosphatase, maltase, and casein-lytic proteinases of the intestinal mucosa is determined within the range from 50 to 60°C, in α-amylase it is shifted towards lower temperatures—10–30°C. A high thermal stability is noted in all investigated enzymes. The maximum level of activity for α-amylase, alkaline phosphatase, and maltase of the intestinal mucosa in the paddlefish Polyodon spatula is within pH 7–9, 9–10, and 6–8, respectively; for casein-lytic proteinases the optimum is at pH 11. In the paddlefish Polyodon spatula, the interaction of nutrients and enzymes of the intestinal mucosa may cause a significant change in the activity level of the enzymes.     

Properties of Brush Border Vesicles Isolated from Rat Kidney Cortex by Calcium Precipitation

Brush border membrane vesicles were isolated from rat kidney cortex by differential centrifugation in the presence of 10 mM calcium. Their properties were compared to brush border vesicles isolated by free-flow electrophoresis. By the calcium precipitation method membrane vesicles were obtained in a shorter time with a similar enrichment of brush border marker enzymes (11- to 12-fold for alkaline phosphatase and maltase), with a similarly reduced activity of the marker enzyme for basal-lateral plasma membranes and an almost identical protein composition as revealed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The transport properties of the two membrane preparations for D-glucose, L-phenylalanine, and phosphate are essentially the same; there is some indication for a lower sodium permeability of the vesicles prepared by the calcium precipitation method. The latter vesicles were also shown to exhibit sodium gradient stimulated uptake of L-glutamate.     

Decreased D-glucose transport across renal brush-border membrane vesicles from streptozotocin-induced diabetic rats

The uptake of Na(+)-dependent D-glucose by renal brush-border membrane vesicles (BBMV) isolated from streptozotocin-induced diabetic rats was decreased as compared with controls. Since a Vmax of 4.8 nmol/mg protein per 30 s in diabetic BBMV was significantly decreased as compared with that of controls (Vmax = 7.0 nmol/mg protein per 30 s) without changing an apparent affinity for D-glucose, the decrease in the Na(+)-dependent D-glucose uptake in diabetic rats is likely to be due to the reduction in the number of the transporter. These results are also confirmed by the binding study of [3H]phlorizin to diabetic BBMV. When the blood glucose level is lowered in diabetic rats by both the treatment with insulin and starvation, the decreased Na(+)-dependent D-glucose uptake is returned to control level. These results suggest that Na(+)-dependent D-glucose reabsorption through the apical membrane in proximal tubular kidney cells is dynamically regulated by the change in blood glucose level.