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Biomedical subjects

A Sandra

Publications and source records attributed to A Sandra.

At least 73 records · Page 4Linked to original sources
PubMed1983

Giant axonal neuropathy: normal protein composition of neurofilaments.

A 14-year-old boy had progressive weakness and ataxia since two years of age with tightly curled hair, facial diplegia, distal weakness and hypaesthesia, cerebellar syndrome and normal intelligence. He also had distal renal tubular acidosis manifested by metabolic acidosis. Sural nerve ultrastructure showed numerous giant axons packed with neurofilaments. The neurofilament major proteins of 68 000, 160 000 and 210 000 daltons found in normal sural nerve were also present in the diseased nerve indicating that the protein composition of neurofilaments which accumulates in this disorder has not been appreciably altered. The amount of 68 000 dalton neurofilament protein was two times higher in giant axonal neuropathy nerve than in the control nerve. Our results suggest that the neurofibrillary pathology in giant axonal neuropathy is due to a build-up of normal neurofilaments.

Acidosis, Renal Tubular↗
PubMed1983

Insulin binding to microvascular endothelium of intact heart: a kinetic and morphometric analysis.

We have studied insulin binding to blood vessels of the intact, beating heart. The beating hearts were perfused with [125I]iodoinsulin (3 X 10(-10) M) followed by perfusion with unlabeled insulin. The unlabeled insulin displaced the bound [125I]iodoinsulin in direct proportion to the concentration of the unlabeled hormone. Perfusion with unlabeled insulin at 10(-11) M elicited a significant displacement of [125I]iodoinsulin, with a maximal effect at 10(-6) M. Unlabeled proinsulin also displaced [125I]iodoinsulin in a dose-dependent manner, being 1% as potent as insulin. Perfusion with unrelated peptides had no effect. Radioautographic counting of 125I grains indicated that greater than 95% of the grain counts over blood vessels were within the microvessels. When [125I]iodoinsulin perfusion was followed by perfusion with unlabeled insulin at 10(-6) M, there was a 50% decrease in grain counts over the microvessels (versus perfusion with [125I]iodoinsulin alone); with coperfusion of [125I]iodoinsulin and 10(-6) M unlabeled insulin, an 80% decrease in grain counts occurred. Electron microscopic radioautography indicated that the 125I grains were associated with the vascular endothelial cells. We conclude that specific insulin receptors are present on endothelial cells of microvessels in the intact heart.

Animals↗
PubMed1982

Collagen synthesis by Duchenne myogenic clones: pathogenic implications for the disease.

Myogenic cell clones were grown in triplicates from a 3-year-old boy with Duchenne muscular dystrophy and three normal control boys matched for age. The well-differentiated Duchenne myogenic clone had lower creatine kinase activity and lower MM isozyme than the control clones. Analysis of (3H)-proline incorporation demonstrated a 2.2-fold increase in (3H)-hydroxyproline released into the medium of Duchenne myogenic cell clones, whereas intracellular (3H)-hydroxyproline levels showed normal values. These results strongly suggest that the increased amount of collagen present in Duchenne dystrophic muscle is related to the primary defect of the disease and is not due to a secondary replacement fibrosis.

Child, Preschool↗
PubMed1982

The effect of membrane phospholipid modification on insulin action in adipocytes from normal and streptozotocin-induced diabetic rats.

The effects of membrane phospholipid modification on insulin-stimulated hexose transport and antilipolysis was studied in isolated adipocytes derived from normal and streptozotocin (STZ)-diabetic rats. The marked inhibition of glucose transport observed in normal adipocytes pretreated with phospholipid vesicles composed of dioleoylphosphatidylcholine and phosphatidylserine (DOPC-PC) was not apparent in cells from diabetic animals. Inhibition of glucose oxidation in cells from non-diabetic, but not diabetic rats, was also detected under conditions where transport rate was insufficient to saturate the intracellular processes leading to oxidation. The antilipolytic effect of insulin, on the other hand, was not significantly impaired by vesicle pretreatment of cells from either the control or diabetic animals. These studies suggest that vesicles may have a specific effect on the glucose transport system and that changes in responsiveness of insulin-stimulated glucose transport may be related to alterations of membrane phospholipids.

Adipose Tissue↗
PubMed1982

Effects of liposome-adipocyte interaction on calcium binding and insulin action.

The interaction of phosphatidylserine (PS)-containing liposomes with isolated rat adipocytes under conditions of liposome-cell fusion or endocytosis was accompanied by an increase in adipocyte membrane calcium binding in both the basal and insulin-stimulated state. In vesicle-treated adipocytes, insulin-stimulated 2-deoxyglucose uptake was inhibited and not as dependent on external calcium concentration as in control cells. These data suggest that the inhibition of insulin-stimulated 2-deoxyglucose uptake in vesicle treated adipocytes may result from the binding of calcium to the exogenously introduced phospholipid at the expense of membrane constituents normally involved in insulin-stimulated calcium binding. This is supported by the observations that 1) the calcium ionophore A23187 increased intracellular calcium levels, yet had no effect on insulin-stimulated hexose uptake; and 2) treatment of intact adipocytes with phospholipase A2 after the cells had been incubated with vesicles resulted in a decrease in membrane associated Ca++ and exogenous phosphatidylserine, which is consistent with a direct role of membrane phosphatidylserine in calcium binding.

Adipose Tissue↗
PubMed1982

Selective isoactin release from cultured embryonic skeletal muscle cells.

The culture medium of embryonic quail myoblasts, labeled for 24 h with [35S]L-methionine, was analyzed by two-dimensional gel autoradiography. The major polypeptide observed had a 43,000 molecular weight and an isoelectric point of 5.4. This polypeptide could be specifically adsorbed to DNAse-I Sepharose. A tryptic peptide map of the [35S]methionine-labeled peptides of intracellular actin and the extracellular major polypeptide were virtually identical. These findings identify the released polypeptide as actin. A comparison of two-dimensional gel patterns of intracellular and extracellular labeled polypeptides showed a large number of differences indicating the actin release did not result from general cellular breakdown. The released actin was not filamentous as judged by its behavior during Bio-Gel A-5m chromatography (Bio-Rad Laboratories, Richmond, Calif.) The released actin did not originate solely from contaminating fibroblasts in the culture because actin was also observed in the medium in clonal myoblast cultures and in purified myotube preparations. Finally, the nonmuscle isoactins, as opposed to muscle alpha-isoactin, were released preferentially. These results indicate that within the developing muscle cell where both muscle and nonmuscle specific isoactins are simultaneously present, the different isoactins may be physically or functionally compartmentalized with the nonmuscle isoactins existing primarily at or near the cell surface.

Actins↗
PubMed1981

Alterations in lipid incorporation in Duchenne muscular dystrophy. Studies of fresh and cultured muscle.

The incorporation of [3H] glycerol into lipids of fresh and cultured skeletal muscle obtained from patients with Duchenne muscular dystrophy (DMD), patients with myotonic dystrophy (My Dyst), controls, and aborted fetuses (10-12 weeks old) was studied. A significant increase of specific incorporation of [3H] glycerol into phosphatidylcholine (PCh), phosphatidylserine (PS), phosphatidylinositol (PI), and triglycerides (TRI) was found in DMD and fetal muscle in both fresh and cultured muscle. No significant differences, however, were noted between the values of glycerol incorporation in DMD and fetal muscle. The ratio between phospholipids and TRI changed significantly for fresh muscle in DMD (3.5) and fetal muscle (4.9) versus controls (24). The incorporation of glycerol into these lipids in My Dyst fresh and cultured muscle showed the same value as controls when expressed both as incorporation/mg protein and ratio between phospholipids and TRI.

Adolescent↗
PubMed1981

Acyltransferase activity and cytochemical localization in differentiating neuroblastoma.

Acyltransferase (AT) enzyme activity was assayed biochemically and localized cytochemically in neuroblastoma monolayers to investigate the possible role of the enzyme in neuroblastoma differentiation and neurite extension. Treatment of cultures for 1 day with serum-free medium or Ro20-1724, a cyclic AMP phosphodiesterase inhibitor, induced neurite outgrowth but did not alter acyltransferase activity. Treatment for 4 days with dexamethasone or Ro20-1724 induced neurite outgrowth and a doubling of enzyme activity per cell. Chromatographic separation of lipid classes indicated that dexamethasone enhanced triacylglyceride synthesis. Acyltransferase was localized in mitochondria of neuroblastoma cells. The results show that 1) dexamethasone stimulates the storage lipid metabolic pathway in neuroblastoma cells and 2) increased acyltransferase activity is concomitant with dexamethasone-induced morphological differentiation. However, AT activity and neurite extension may not be causally related.

1-Acylglycerol-3-Phosphate O-Acyltransferase↗
PubMed1981

Effect of liposome-adipocyte interaction on hexose uptake and insulin action.

The effect of unilammelar lipid vesicles composed of defined acyl chain phosphatidylcholines or binary vesicles comprised of dioleoyl phosphatidylcholine (DOPC) and a variety of other lipid species on insulin action in isolated rat adipocytes was studied. Cells were treated with vesicles and subsequently analyzed for basal and insulin-stimulated hexose uptake. Of the different vesicles tested, only those containing DOPC and phosphatidylserine (PS) markedly inhibited the effect of insulin. The inhibition was a function of PS concentration in the binary vesicle. Basal uptake, on the other hand, was stimulated by PS-containing vesicles. The changes in insulin-stimulated hexose uptake following interaction of adipocytes with DOPC-PS vesicles were accompanied by alterations in the Vmax of the uptake process and in affinity of insulin binding, although the similar ED50 values of the control and vesicle-treated groups suggest that the observed effects on insulin sensitivity may be mediated by an uncoupling of the insulin receptor from transport activation. Several lines of evidence are consistent with vesicle-cell fusion as the pathway of DOPC-PS uptake under these conditions. Fluorescence microscopic analysis of fat cells following their interaction with vesicles filled with fluorescent dye indicated that the internal contents of the adipocytes became generally labeled. Biochemical studies of cell fractionation after the interaction of adipocytes with radiolabeled vesicles and effects of metabolic inhibitors and cell fixatives on vesicle uptake also support the fusion pathway.

Adipose Tissue↗
PubMed1979

Reversal by insulin of concanavalin A inhibition of myotube formation and evidence for common binding sites.

Concanavalin A (Con A) inhibits fusion of trypsin-treated myoblasts. This inhibition is reversed by the addition of supraphysiological concentrations (4 micrograms/ml) of insulin either during continuous presence in culture or by pulse additions at 36 and 48 h of culture, just before the time that cultures not treated with Con A undergo myoblast fusion. This reversal is not due to the mitogenic effects of insulin. Under reversal conditions, no specific displacement of bound [125I]iodo-Con A was detected nor did insulin stimulate metabolite uptake. Cell surface replicas of hemocyanin-tagged Con A showed that insulin reversal of the inhibition of myotube formation correlated with the alteration of Con A-binding sites from a clustered configuration present in the inhibited cells to a dispersed state correlated with normal myotube formation. Although a causal relationship has yet to be shown, the data suggest that insulin-mediated reversal of Con A inhibition of myoblast fusion may be related to the ability of insulin at supraphysiological levels to alter the translational mobility of cell surface components containing glucose and/or mannose residues capable of binding Con A. Evidence is presented which suggests that insulin and Con A share common binding sites, since in the physiological range of insulin concentrations (1 ng/ml), Con A pretreatments results in an inhibition of specific [125I]iodo-insulin binding, and antagonistic interactions of insulin and Con A on metabolite uptake and cell proliferation occur. Thus, it appears that the insulin receptors of developing skeletal muscle are glycoproteins containing glycopyranosides.

Animals↗