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S Segal

Publications and source records attributed to S Segal.

At least 307 records · Page 17Linked to original sources
PubMed1986

Developmental aspects of proline transport in rat renal brush border membranes.

Proline uptake by rat renal brush border membrane vesicles from animals 7 days of age and older has been examined to delineate developmental changes in membrane function that may underlie the physiological hyperprolinuria of young animals. Although the two proline transport systems normally present in adult membranes were found in membranes from young animals, the proline "overshoot" resulting from a sodium ion gradient is minimal and increases with age of the animal from which the membranes were isolated. This is associated with a severalfold faster entry of 22Na into vesicles of the 7-day-old animal compared to entry into membranes prepared from adult kidneys. The very rapid dissipation of the sodium gradient thus diminishing the driving force for transmembrane proline movement may explain the changes in proline overshoot observed in membranes from young animals. The altered sodium permeability is consistent with the fact that young animals have a generalized inability to reabsorb other amino acids whose transport is known to be sodium gradient stimulated.

Age Factors↗
PubMed1986

Phosphatidylinositol:myo-inositol exchange activity in intact nerve endings: substrate and cofactor dependence, nucleotide specificity, and effect on synaptosomal handling of myo-inositol.

Micromolar concentrations of CMP produced a large increase in Mn2+-dependent phosphatidylinositol:myo-inositol exchange activity in isolated nerve endings or synaptosomes. The apparent Km for CMP was 2 microM, and that for myo-inositol was 38 microM. Only cytidine nucleotides were capable of enhancing activity, and this effect is probably specific for CMP, because the synaptosomal preparation rapidly converted CTP or CDP to CMP. Manganese did not affect the uptake of myo-inositol into the synaptosomal cytosolic fraction or myo-inositol levels. Determinations of myo-inositol specific activity showed that the Mn2+-enhanced labeling of phosphatidylinositol was not accompanied by a decrease of label content in free myo-inositol. This lack of an effect on intrasynaptosomal myo-inositol and the dependence of exchange on cytidine nucleotides whereas cytidine itself was previously found to be without effect show that for the bulk of Mn2+-dependent exchange activity, it is the myo-inositol in the incubation medium that is being directly incorporated into membrane-bound phosphatidyl-inositol. Because CMP dependence is the hallmark of exchange catalyzed by CDP-diacylglycerol:inositol phosphatidyl transferase, this enzyme is likely to be responsible for most of the exchange activity in synaptosomes. The strong affinity of this exchange system for CMP suggests that endogenous levels of this nucleotide might support Mn2+-dependent exchange in the absence of added nucleotide.

Animals↗
PubMed1986

Lysine uptake by rat renal brush-border membrane vesicles.

Lysine uptake by isolated rat renal brush-border membrane vesicles occurs via a single saturable system plus a significant diffusion component with indication of a single energy of activation on an Arrhenius plot. Initial uptake is not sodium dependent, and intravesicular accumulation of lysine at longer time points is greatest in the absence of sodium. Accumulation levels differ in the presence or absence of NaCl or choline chloride and are specific for the cation used. Lysine uptake is membrane potential sensitive and inhibitable by cystine, dibasic amino acids, and cycloleucine. Heteroexchange diffusion of lysine with cystine and lysine with arginine occurs, but no heteroexchange occurs with cycloleucine, indicating that lysine shares a transport system with cystine and dibasic amino acids but not with cycloleucine.

Amino Acids↗
PubMed1986

Nitrogen sources for renal ammoniagenesis: study with 15N amino acid.

The contribution of amino acids other than glutamine to renal ammoniagenesis was investigated in renal tubules obtained from control rats and rats with metabolic acidosis by incubating 2.5 mM [5-15N]glutamine, [2-15N]glutamine, [15N]glutamate, [15N]aspartate, [15N]alanine, or [15N]glycine, either as the sole N source in Krebs bicarbonate buffer or as a labeled substrate in a medium containing a mixture of unlabeled amino acids. With control tissue in Krebs buffer, approximately 75% of total ammonia was derived from 5-N of glutamine, whereas 2-N of glutamine, glutamate, aspartate, alanine, and glycine supplied 1, 10, 13, 4, and 18%, respectively. In the acidotic state, these values were 51, 30, 30, 30, 10, and 15% of the total ammonia produced, respectively. The ammonia that could not be accounted for by 15N analysis was derived from endogenous sources. Studies with tubules incubated in Krebs medium alone indicated that, in both control and acidosis, the calculated fraction of ammonia derived from endogenous sources was significantly decreased by addition of either 0.7 or 2.5 mM glutamine. However, ammonia production from endogenous sources was similar whether 0.7 or 2.5 mM glutamine was used as a sole exogenous substrate. Incubations of control tissue in buffer supplemented with an amino acid mixture revealed a significant decrease in ammonia production from [5-15N]glutamine compared with incubation in Krebs buffer alone. In chronic acidosis, no significant difference was found in total ammonia formation from [5-15N]glutamine compared with Krebs buffer alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1986

Developmental aspects of cystine transport in the dog.

Developmental changes in cystine transport by the canine kidney were examined both in vivo and in vitro. Renal clearance studies indicated that cystine was one of the more incompletely reabsorbed amino acids at birth, but its reabsorption approaches adult levels by 21 days. Concomitantly, cystine uptake by isolated renal cortical tubule fragments from immature dogs was slower than that by renal tubules from adult dogs. Both age groups rapidly metabolized the transported cystine. This metabolism was principally to cysteine, but also small amounts of reduced glutathione were formed from the transported cystine. Concentration dependence studies indicated two transport systems for cystine uptake in both the immature and the adult dog. Both transport systems in the 1-wk-old dog had a somewhat greater affinity for cystine than the corresponding system in the adult, but this was offset by the markedly lower maximal transport rates for these systems in the 1-wk-old dog. The high affinity system was inhibited by lysine in tubules from both age groups. In the dog, the rise in the tubular reabsorption of cystine with maturation could, in part, be explained by an increase in the number of transport sites for cystine.

Animals↗
PubMed1986

General anesthesia during excision of a mouse tumor accelerates postsurgical growth of metastases by suppression of natural killer cell activity.

Our previous studies indicated that anesthetic drugs cause acceleration of postoperative metastasis of mouse tumors. We tested whether this augmentation could be attributed to a decrease in natural killer (NK) activity. The results indicated that two of the anesthetic drugs used during excision of the Lewis lung carcinoma (3LL) tumor, halothane and ketamine, decreased NK activity, whereas the other two, thiopental sodium and N2O, had no effect on NK activity in in vitro assays. The observed decrease in NK cell activity was reversed following treatment with polyinosinic-polycytidylic acid (poly I:C), which is an NK cell potentiator. Treatment of mice with poly I:C abolished the accelerated growth of metastases following excision of the tumor under ketamine or halothane anesthesia. On the other hand, treatment with poly I:C seemed to have no effect on acceleration of postoperative metastasis in mice anesthetized with N2O or thiopental sodium.

Anesthesia, General↗
PubMed1985

Metabolism of glutamine and glutamate by rat renal tubules. Study with 15N and gas chromatography-mass spectrometry.

Gas chromatography-mass spectrometry was utilized to study the metabolism of [15N]glutamate, [2-15N]glutamine, and [5-15N]glutamine in isolated renal tubules prepared from control and chronically acidotic rats. The main purpose was to determine the nitrogen sources utilized by the kidney in various acid-base states for ammoniagenesis. Incubations were performed in the presence of 2.5 mM 15N-labeled glutamine or glutamate. Experiments with [5-15N]glutamine showed that in control animals approximately 90% of ammonia nitrogen was derived from 5-N of glutamine versus 60% in renal tubules from acidotic rats. Experiments with [2-15N]glutamine or [15N]glutamate indicated that in chronic acidosis approximately 30% of ammonia nitrogen was derived either from 2-N of glutamine or glutamate-N by the activity of glutamate dehydrogenase. Flux through glutamate dehydrogenase was 6-fold higher in chronic acidosis versus control. No 15NH3 could be detected in renal tubules from control rats when [2-15N]glutamine was the substrate. The rates of 15N transfer to other amino acids and to the 6-amino groups of the adenine nucleotides were significantly higher in normal renal tubules versus those from chronically acidotic rats. In tubules from chronically acidotic rats, 15N abundance in 15NH3 and the rate of 15NH3 appearance were significantly higher than that of either the 6-amino group of adenine nucleotides or the 15N-amino acids studied. The data indicate that glutamate dehydrogenase activity rather than glutamate transamination is primarily responsible for augmented ammoniagenesis in chronic acidosis. The contribution of the purine nucleotide cycle to ammonia formation appears to be unimportant in renal tubules from chronically acidotic rats.

Acid-Base Equilibrium↗
PubMed1985

Topoisomerase-II activity in human leukemic and lymphoblastoid cells.

Topoisomerase-II activity was analyzed in various human leukemic and lymphoblastoid cell-lines with comparison to normal human peripheral blood lymphocytes. All of the examined tumor cells contained this enzyme in both the nuclear and cytoplasmic fractions, whereas no appreciable activity of the enzyme was detected in either fraction of the resting normal lymphocytes. Using pBR322 plasmid as a substrate, undialyzed extracts of the tumor cells exhibited the typical ATP-dependent relaxation of supercoiled circles and formation of linear and catenated structures, as well as the ATP-independent knotting activity. On the other hand, dialyzed extracts exerted only the ATP-dependent supercoil relaxation. Novobiocin inhibited the linearization and catenation but not the supercoil relaxing or knotting activities. This study provides indications for an excessive level of a structurally abnormal topoisomerase-II in these tumor cell-lines.

Adenosine Triphosphate↗
PubMed1985

Decreased procollagen production in cultured fibroblasts from patients with Lowe's syndrome.

The oculo-cerebro-renal syndrome described by Lowe is a catastrophic disease in children characterized by progressive eye, central nervous system and kidney degeneration. We determined procollagen production in cultured skin fibroblasts originating from patients with Lowe's syndrome as well as normal individuals after incubation of cells with [14C]proline for 1,4 and 20 h. Using [14C]hydroxyproline formation, in relation to cell protein or DNA, as an index of procollagen production, we found that cultured cells from patients synthesized collagenous protein at a substantially reduced level. This decrease in synthesis in cultured fibroblasts from patients could not be accounted for by differences in the specific radioactivity of the free intracellular proline; moreover, it could not be attributed to differences in the kinetics of growth between normal and affected cell lines. The degree of hydroxylation of proline residues in collagen was the same in both normal and affected cells.

Cells, Cultured↗
PubMed1985

Uptake of proline by brushborder vesicles isolated from human kidney cortex.

Proline transport into renal brushborder membrane vesicles isolated from human kidney is mediated by two uptake systems. The high-affinity system is stimulated by a Na gradient and appears to be shared with glycine while the low-affinity system is not. Uptake curves of low concentrations of proline exhibit a Na-gradient-dependent overshoot indicative of electrogenic transport. The proline transport systems observed in isolated human renal brushborder membrane vesicles appear to have characteristics similar to those in rat kidney membranes.

Alanine↗
PubMed1985

Evolutionary conservation of brain Thy-1 glycoprotein in vertebrates and invertebrates.

The evolutionary conservation of brain Thy-1 glycoprotein in 24 vertebrate and invertebrate species has been investigated by means of a soluble phase radioimmunoassay (RIA) and by the "Western blot" technique. The brain glycoproteins from virtually all the vertebrate species inhibited the precipitation of mouse Thy-1.1 by a rabbit anti-rat Thy-1 antiserum. Most reagents also inhibited the binding of a mouse anti-rat Thy-1 monoclonal antibody to rat Thy-1. Whole tissue glycoproteins from earthworm, snail and oyster and ganglia glycoproteins of a locust species were also found to be inhibitory. Western blotting analysis on NaDod SO4 polyacrylamide gel electrophoresis under reducing conditions revealed a Thy-1 homologous molecule (22-25 KD) in mammals, birds, fish, reptiles and invertebrate species. The snail Thy-1-like molecule was eluted from the gel and was shown to specifically inhibit the serological reaction. The rabbit anti-rat Thy-1 antiserum also detected a doublet molecule of approximately 85,000 KD, which is conserved in all species, including yeast and bacteria. The origin and nature of the presumed glycoproteins is unknown. Our results suggest that the Thy-1 molecule has been conserved throughout metazoan evolution and that the Thy-1 gene is the most conserved among the immune related genes (immunoglobulins, beta 2-microglobulin and major histocompatibility) which share extensive amino acid homology.

Animals↗
PubMed1985

"Retroposon" insertion into the cellular oncogene c-myc in canine transmissible venereal tumor.

We examined by Southern blotting the state of the cellular oncogene c-myc in the dog transmissible venereal tumor. The tumor DNA contains a 16.8-kilobase pair (kbp) rearranged c-myc fragment in addition to the normal 15-kbp and 7.5-kbp fragments. We compared the structure of the cloned rearranged c-myc (re-myc) with that of a cloned normal c-myc and found that the rearrangement was due to the insertion of a 1.8-kbp DNA upstream to the first exon of c-myc. The inserted DNA is flanked by 10-base-pair direct repeats and contains a dA-rich tail, suggesting its origin from mRNA. Partial sequence of the inserted element showed 62% homology with the primate interdispersed Kpn I repetitive element. These results provide an example for the behavior of repetitive DNA sequences like the Kpn I family, as movable elements that can transpose nearby to oncogenes or other structural genes and perhaps affect their activity.

Animals↗
PubMed1985

Levamisole circumvents inhibition of lymphocyte activation imposed by uremic serum.

Uremic serum inhibits thymidine incorporation of phytohemagglutinin-stimulated lymphocytes originating in normal individuals. In this study the effect of levamisole on such inhibition was investigated. Preincubation with a wide range of levamisole concentrations resulted in complete prevention of the inhibitory effect imposed by uremic serum on thymidine incorporation. We would like to suggest that uremic serum possibly inhibits thymidine incorporation of normal lymphocytes by imposing an abnormal cyclic GMP/cyclic AMP intracellular ratio, and that levamisole may restore this ratio to normal.

Adolescent↗
PubMed1985

Proteolytic enzymes in tumor metastasis. II. Collagenase type IV activity in subcellular fractions of cloned tumor cell populations.

Collagenase type IV degradation activity was examined in metastatic and nonmetastatic clones of the Lewis lung carcinoma (3LL) and of the T10 sarcoma. Conditioned media prepared from cells of both tumors grown in vitro contained low degradation activities, whereas conditioned media from organ cultures of the same clones grown as solid tumors in animals exhibited higher degradation activities. Analysis of subcellular fractions of tumor cells showed that collagenase type IV activity was localized mainly in the cytoplasmic fraction. Crude homogenates or detergent lysates manifested low degradation activities. Little activity was associated with purified plasma membrane preparations and endoplasmic reticular fractions. However, addition of plasma membrane to conditioned media and to cytoplasmic fractions reduced the degradation activities of the cytoplasmic fractions. Possibly a factor that inhibits collagenase type IV exists in the cells in a vesicular form. No correlation between degradation activity and metastatic capacity was demonstrated in the models used in this study. Both metastatic and nonmetastatic clones of the same tumor similarly could degrade basement membrane components.

Animals↗
PubMed1985

Segregation of peripheral blood lymphocytes in sarcoidosis according to their affinity to insolubilized histamine.

Using a method based on the differential affinity of mononuclear cells to insolubilized histamine, we were able to distinguish several differences in the composition of T cell subpopulations between healthy control subjects and sarcoidosis patients. In 5 of 10 patients with sarcoidosis, the ability of T cells to respond to three mitogens was severely depressed, while in the remaining 5 it was similar to the response of normal subjects. After the elimination of a subpopulation of peripheral blood mononuclear cells (PBMC) that adhered to the histamine column, the response to mitogens of the unbound cells of normal control subjects was significantly lower than values obtained before separation. The histamine-unbound lymphocytes of the five patients with active sarcoidosis, whose unseparated PBMC responded poorly to mitogens, reacted significantly better to the mitogens than before the separation. This pattern of responsiveness has been previously only in PBMC of patients with autoimmune diseases. It seems that some patients with sarcoidosis possess a subpopulation of T-lymphocytes with suppressor activity and a specific affinity to insolubilized histamine, the elimination of which restores the level of response to almost normal.

Adult↗
PubMed1985

Proteolytic enzymes in tumor metastasis. I. Plasminogen activator in clones of Lewis lung carcinoma and T10 sarcoma.

Plasminogen activator (PA; urokinase) levels were studied in metastatic and nonmetastatic clones of the Lewis lung carcinoma (3LL) and of the T10 sarcoma. Tests of clones grown in vitro revealed that the cell content and secretion of PA correlated positively with the metastatic capacity of the clones of both tumors. When cell-associated activities were examined in cloned cell populations grown subcutaneously in vivo, the apparent activities in the solid tumors produced by low-metastatic clones were equal to or even higher than those in solid tumors produced by high-metastatic clones. This finding was attributed to the observation that solid tumors produced by low-metastatic clones, but not those produced by high-metastatic clones, were highly infiltrated with macrophages. Subsequent tests indicated that the ip inoculation of X-irradiated or mitomycin-treated tumor cells of low-metastatic clones elicited a significantly greater peritoneal infiltration of macrophages than did tumor cells of high-metastatic clones. Such "tumor-associated" macrophages manifested high levels of PA, whereas resident (nonactivated) peritoneal macrophages did not. These findings suggest that although PA may cause the initial detachment from the local tumor of both nonmetastatic (via the macrophage PA) and metastatic cells (via their own PA), the PA secreted by the metastatic cells may enable them to complete subsequent stages of the metastatic process that may be PA-dependent.

Animals↗
PubMed1985

Selecting, accelerating and suppressing interactions between macrophages and tumor cells.

Studies were carried out to test whether thioglycollate-induced macrophages (T-PM phi) exert a selective effect on 3LL tumor cells. One million 3LL tumor cells and 10 X 10(6) thioglycollate-elicited peritoneal macrophages were admixed and inoculated subcutaneously in C57BL/6 mice. This procedure was repeated for a series of 6-15 consecutive transplant generations. After 6 generations, the tumor cells which were selected in this manner (3LLR6) grew faster in vivo and in vitro when admixed with T-PM phi than 3LL cells which were not selected by T-PM phi. However, in vivo, this T-PM phi-mediated acceleration of 3LLR6 tumor growth was followed by tumor rejection and induction of anti-3LL immunity. Intravenous inoculation of T-PM phi enhanced the growth of pulmonary metastases in mice subsequently inoculated intravenously with 3LL cells. Such T-PM phi-mediated augmentation of metastases was not observed with 3LLR6 cells. Homing of 3LL and 3LLR6 cells to the lungs after pretreatment with T-PM phi was similar, indicating that these cells did not differ in their capacity to colonize the lungs but rather in subsequent tumor growth. Additional transplantations of 3LLR6 cells with T-PM phi led, after 9 further transplant generations, to a different tumor cell, 3LLR15, with completely new morphological, tumorigenic and metastatic properties. Unlike the 3LLR6 cells, this variant was not sensitive to the growth promoting effects of T-PM phi. Furthermore, it expressed the H-2K-and H-2D-encoded antigens of the H-2b haplotype, whereas the 3LL and 3LLR6 cells expressed only the H-2D alloantigens. This indicates that macrophages may either exert a selective effect on tumor cells or play a role in the induction of new tumor cells.

Animals↗