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Biomedical subjects

F G Toback

Publications and source records attributed to F G Toback.

At least 73 records · Page 4Linked to original sources
PubMed1981

New form of acid phosphatase during lysosome biogenesis.

Lysosome formation was induced in cells of the renal medulla by feeding rats on a K+-deficient diet. The role of the endoplasmic reticulum in the production of acid phosphatase, a typical lysosomal enzyme, was examined. Lysosomal and microsomal fractions were prepared for study by differential centrifugation of homogenates of renal papilla and inner stripe of red medulla. Acid phosphatase activity in the microsomal fraction was distinguished from the activity in the lysosomal fraction in normal tissue by differences in pH optima, tartrate inhibition, distribution of multiple forms after polyacrylamide-gel electrophoresis and detergent-sensitivity. During progressive K+ depletion, acid phosphatase activity in both microsomal and lysosomal fractions of the tissue increased 3-fold. In the lysosomes, K+ depletion was associated with the appearance of a new band of acid phosphatase. The neuraminidase-sensitivity of this band on polyacrylamide-gel electrophoresis indicated that the enzyme protein had been modified by the addition of sialic acid residues. K+ depletion also altered the lysosomal enzyme so that thiol compounds were able to stimulate its activity.

Acid Phosphatase↗
PubMed1980

Induction of growth in kidney epithelial cells in culture by Na+.

The role of Na+ in the regulation of cell growth was examined in quiescent, high-density cultures of kidney epithelial cells of the BSC-1 line. The addition of NaCl to the medium increased the number of cells initiating DNA synthesis in a concentration-dependent manner after serum stimulation. In the presence of added NaCl, cells in confluent cultures grew to high density at an increased rate, whereas growth in sparse cultures was retarded. These results suggest that, in the presence of serum, Na+ can act as a mediator of the events that initiate cell proliferation.

Animals↗
PubMed1980

Amino acid modulation of renal phosphatidylcholine biosynthesis in the rat.

The hypothesis that amino acids act as modifiers of phospholipid biosynthesis was tested in renal cortical cells from normal rats. The rate of [14C]-choline incorporation into phospholipid in cortical slices was enhanced by the addition of lysine or arginine to the incubation medium, and reduced by phenylalanine, aspartic acid, or four other amino acids. Lysine and aspartic acid appeared to modify the cholinephosphotransferase reaction in which cytidine 5'-diphosphocholine (CDP-choline) and 1,2-diacylglycerol react to form phosphatidylcholine, the major phospholipid of renal membranes. Since this enzymatic reaction takes place in the endoplasmic reticulum, the effect of single amino acids on microsomal preparations was examined. Lysine increased CDP-choline:1,2-diacylglycerol cholinephosphotransferase activity by 95%, whereas aspartic acid reduced activity by 65%, in a concentration-dependent manner. For both substrates in the reaction, amino acids modulated enzyme activity by altering the maximum velocity without changing the apparent Km. These observations in intact renal cells and in microsomal preparations indicate that changes in cellular amino acid concentrations could modify the biosynthetic rate of phosphatidylcholine, and suggest a mechanism that could coordinate the biosynthesis of phospholipid and protein.

Amino Acids↗
PubMed1979

Amino acid-mediated stimulation of renal phospholipid biosynthesis after acute tubular necrosis.

The mechanism by which amino acid infusion stimulates membrane physpholipid biosynthesis during renal regeneration after mercuric-chloride-induced acute tubular necrosis was studied in the rat. Amino acids can act directly on regenerating renal tissue to enhance net phospholipid synthesis because preincubation of cortical slices with amino acids induced an increase in [14C]-choline incorporation into phospholipid without altering the rate of breakdown. This amino acid stimulation of phospholipid biosynthesis was studied further by measuring [14C]-choline accumulation and its sequential conversion to phosphorylcholine, cytidine diphosphocholine (CDP-choline), and phosphatidylcholine via the Kennedy pathway in regenerating renal tissue. [14C]-Choline accumulation was increased after amino acid infusion, compared to glucose infusion. There were also increments in the Vmax of the choline kinase reaction, which converts entering [14C]-choline into [14C]-phosphorylcholine, and of the cholinephosphotransferase reaction in which [14C]-CDP-choline is incorporated into [14C]-phosphatidylcholine, whereas the apparent Km of each reaction was unchanged. Thus, amino acids infused after tubular necrosis can act directly on regenerating renal cells to increase precursor availability and augment two reactions of the phospholipid biosynthetic pathway.

Acute Kidney Injury↗
PubMed1977

Phospholipid metabolism during renal regeneration after acute tubular necrosis.

Renal function, structure, and membrane metabolism were studied during regeneration of proximal tubular cells in rats. A reversible syndrome of nonoliguric acute renal failure was induced by the intravenous administration of a low dose of mercuric chloride (1.0 mg Hg/kg). At day 1 there was a marked increase in serum urea nitrogen concentration (SUN), decrease in food intake, and a zone of proximal tubular cell necrosis in the inner cortex. By day 3 low cuboidal epithelial cells were seen, indicating that regeneration had been initiated despite decreased food intake and increasing SUN. Phospholipid synthesis for new membrane formation in regenerating cells was studied by using [14C] choline as a precursor of phosphorylcholine and cytidine diphosphocholine (CDP-choline), which are intermediates in the synthesis of renal choline-containing phospholipid. The rate of [14C]choline incorporation into phospholipids in inner cortical slices was lowest 1 day after mercury administration, then increased constantly for the next 4 days to reach a maximal value 104% above control. The rate declined slowly for the next 11 days and returned to normal by 28 days. The increased rate represented choline phosphoglyceride synthesis, since degradation was unchanged. The entire increment in choline radioactivity in regenerating tissue 2 and 3 days after mercury administration was in phospholipid or CDP-choline, which suggests that the increased number of choline molecules entering the growing cells were trapped in these two forms. The results indicate that renal regeneration is associated with a specific enhancement of the synthesis of choline-containing phospholipids. This anabolic response of the kidney occurs in the presence of systemic catabolism and progressive renal functional insufficiency.

Acute Kidney Injury↗
PubMed1977

Stimulation of renal phospholipid formation during potassium depletion.

Potassium depletion induces increased membrane phospholipid formation and renal growth in rats. To determine the mechanism by which potassium depletion augments phospholipid formation, the metabolism of radioactive choline, a precursor of choline-containing phospholipids, was studied in renal slices. Cortical and medullary tissue from potassium-depleted and control animals accumulated extracellular choline and sequentially converted it to phosphorylcholine, cytidine diphosphocholine (CDP-choline), and choline phosphoglyceride, thereby demonstrating that renal cells can utilize the Kennedy pathway for phospholipid synthesis. [14C]Choline uptake into intracellular fluid was increased in cortical slices from potassium-depleted animals. The apparent Km and Vmax of the kinase reaction which converts entering [14C]choline to [14C]phosphorylcholine were unchanged during potassium depletion. The rate of [14C]phosphorylcholine conversion to [14C]CDP-choline was also unchanged. In contrast, the Vmax of [14C]choline phosphoglyceride formation from [14C]CDP-choline was increased, whereas the apparent Km for this reaction was unchanged. These results indicate that increased renal choline phosphoglyceride formation during potassium depletion can occur via the Kennedy pathway and appears to be mediated by increases in choline uptake and the rate of CDP-choline incorporation into phospholipid, the first and last steps of the pathway.

Animals↗
PubMed1977

Zonal changes in renal structure and phospholipid metabolism during reversal of potassium depletion nephropathy.

Structural changes and membrane metabolism were studied in the enlarged kidney of potassium-depleted rats during dietary repletion with potassium. Transmission and scanning electron microscopy of kidneys revealed two patterns of involutionary change in the collecting tubules following potassium repletion. Autophagocytosis was observed within 3 hours in the hyperplastic cells of the inner red medulla, and progressive condensation and reduction in the number and size of lysosomes which had formed during potassium depletion were observed in the renal papilla. After 3 days of potassium repletion, all types of cells had a normal ultrastructural appearance. Alterations in membrane metabolism during autophagocytosis and organelle regression were assessed by measuring the in vivo breakdown of [14C]phosphatidylcholine, phospholipase A activity, and the rate of [14C]choline incorporation into phospholipid in papilla, inner red medulla, and inner cortex. In each tissue the rate of [14C]phosphatidylcholine breakdown increased and the rate of [14C]choline incorporation into phospholipid decreased during potassium repletion. Phospholipase A activity, which was depressed in potassium-depleted animals, increased in each renal zone by 12 hours after potassium repletion. The results indicate that reversal of potassium depletion nephropathy is associated with increased membrane phospholipid catabolism, loss of renal mass, and specific morphologic changes in different renal zones: lysosome regression in the papilla and autophagocytosis in the hyperplastic cells of the inner red medulla.

Animals↗
PubMed1977

Formation of renal medullary lysosomes during potassium depletion nephropathy.

The biochemical correlates of droplet formation in renal inner medullary cells of potassium-deficient rats were studied. An increase in the activities of five hydrolytic enzymes typical of lysosomes was associated with an increase in the number and size of droplets observed during progressive potassium depletion. Acid phosphatase activity increased 7-fold whereas beta-glucuronidase, beta-galactosidase, cathepsin, and acid DNase increased 2- to 4-fold in medullary homogenates at 25 days of depletion. Following potassium repletion the activities returned to normal at a rate dependent upon the duration of potassium depletion. The decreases in enzyme activities were associated with a concomitant rapid disappearance of the droplets from medullary cells. Protein synthesis for new droplet enzyme formation was studied by measuring the rate of [14C]leucine incorporation into protein in medullary slices. The rate increased at 1 day of depletion and reached a maximum which was 139 per cent higher than control after 7 days of depletion. In droplets isolated from medullary tissue during progressive potassium depletion the rate of protein labeling with [14C]leucine and acid phosphatase specific activity increased in parallel. When droplet proteins were separated by gel electrophoresis, acid phosphatase activity was detected in a protein band which had been labeled with [14C]leucine, thereby suggesting new enzyme protein formation. The increase in enzyme and protein synthesis and a previously demonstrated increase in phospholipid synthesis and membrane formation indicate that potassium depletion induces specific alterations in renal inner medullary cell metabolism which result in increased lysosome formation.

Acid Phosphatase↗
PubMed1976

Independence of onset of compensatory kidney growth from changes in renal function.

Renal function was measure before and shortly after uninephrectomy in mice to evaluate if work expended in the reabsorption of glomerular filtrate plays a role in the initiation of compensatory growth. To exclude the possibility of small but undetectable increments in glomerular filtration rate and absolute sodium reabsorption these functions were experimentally reduced immediately after uninephrectomy and sham nephrectomy. The onset of growth was indicated by an increased rate of [14C]choline incorporation into phospholipid in renal cortical slices. [14C]choline incorporation increased significantly only after uninephrectomy and remained unchanged after sham operation regardless of the magnitude or direction of the concurrent change in sodium reabsorption. The rate of incorporation increased by 40 +/- 8% (P less than 0.005) in uninephrectomized animals whose sodium reabsorption was reduced by 34 +/- 6% (P less than 0.001) and rose 45 +/- 11% (P less than 0.005) when sodium reabsorption remained unchanged. These results indicate that compensatory kidney growth is not triggered by an increase in renal work expended in the reabsorption of glomerular filtrate; in fact, it can occur when reabsorptive work is substantially decreased.

Aminohippuric Acids↗
PubMed1976

Zonal changes in renal structure and phospholipid metabolism in potassium-deficient rats.

Morphologic alterations and membrane metabolism were studied in the kidneys of rats fed a low potassium diet. Transmission and scanning electron microscopy following perfusion-fixation of kidneys revealed that the earliest morphologic change occurs in cells of the papillary tip in which multivesicular bodies, a specific type to lysosome, appear after 1 day. Increased depletion leads to extension of the lesion to all cells of the papilla. After 1 week, a narrow band of hyperplasia in the inner red medulla appears; this band is characterized by adenomatous proliferation of intercalated and light cells and partial obstruction of collecting tubules. These alterations and cortical growth in the normal pattern result in increased renal weight. New membrane formation for lysosomes and growing cells was studied by measuring the rate of [14C]choline incorporation into phospholipid in slices from five zones of the kidney. In the papilla the rate increased 39 per cent after 18 hours, the earliest change detected. After 36 hours the rate increased in inner red medulla by 28 per cent, inner cortex by 25 per cent and outer cortex by 40 per cent. [14C]choline was a specific precursor of the three renal phospholipids, phosphatidylcholine, lysophosphatidylcholine, and sphingomyelin. The relative distribution of the label did not change with growth induced by potassium depletion. The results indicate that potassium depletion induces early increases in the formation of cell membrane phospholipid which correlate with specific morphologic changes in different zones within the kidney.

Animals↗
PubMed1974

Phospholipid metabolism in the initiation of renal compensatory growth after acute reduction of renal mass.

Membrane metabolism was studied during the initiation of compensatory growth after acute reduction in renal mass. The rate of [(14)C]choline incorporation into phospholipid in renal cortical slices was increased by 37% at 5 min of compensatory growth in mice. The rate increased to the maximal value of 68% by 20 min and remained there for 3 h. The rate then remained increased at 28-34% above normal for 2 days and returned to normal by the 6th day. The increase in rate of choline incorporation into renal phospholipid was independent of choline uptake. [(14)C]Choline was found to be a specific precursor of the three renal phospholipids, phosphatidylcholine, lysophosphatidylcholine, and sphingomyelin, which comprise over half the amount of the phospholipids. The relative distribution of the label in each of the three phospholipid classes did not change with compensatory growth. An increased rate of choline incorporation was also observed in kidneys of rats during compensatory growth and in the compensating kidneys of mice treated with indomethacin before uninephrectomy. The rate was increased 24% at 3 h after uninephrectomy in vivo. The increase appeared to be specific for the kidney, since it did not occur in the livers of these mice. The results indicate that the onset of renal compensatory growth is associated with a specific enhancement of the synthesis of renal choline-containing phospholipids. Since the phospholipids largely occur in the cell membrane, early alterations in cell membrane metabolism may thus play a role in the initiation of cell growth.

Animals↗