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Biomedical subjects

C Filburn

Publications and source records attributed to C Filburn.

6 recordsLinked to original sources
PubMed1998

Homogenous repair of singlet oxygen-induced DNA damage in differentially transcribed regions and strands of human mitochondrial DNA.

Photoactivated methylene blue was used to damage purified DNA and the mitochondrial DNA (mtDNA) of human fibroblasts in culture. The primary product of this reaction is the DNA lesion 7-hydro-8-oxo-deoxyguanosine (8-oxo-dG). The DNA damage was quantitated using Escherichia coli formamidopyrimidine DNA glycosylase (Fpg) in a gene-specific damage and repair assay. Assay conditions were refined to give incision at all enzyme-sensitive sites with minimal non-specific cutting. Cultured fibroblasts were exposed to photoactivated methylene blue under conditions that would produce an average of three oxidative lesions per double-stranded mitochondrial genome. Within 9 h, 47% of this damage had been removed by the cells. This removal was due to repair rather than to replication, cell loss or degradation of damaged genomes. The rate of repair was measured in both DNA strands of the frequently transcribed ribosomal region of the mitochondrial genome and in both strands of the non-ribosomal region. Fpg-sensitive alkali-resistant oxidative base damage was efficiently removed from human mtDNA with no differences in the rate of repair between strands or between two different regions of the genome that differ substantially with regard to transcriptional activity.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1997

Mitochondrial biogenesis during cellular differentiation.

Mitochondrial biogenesis was studied during differentiation of two immortalized cell lines (C2C12, 3T3) with enzyme measurements, Northern blots, and quantitative ultrastructure. Citrate synthase, isocitrate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase (nuclear encoded, mitochondrial matrix location) showed linear, four- to sixfold increases in enzymatic activity in C2C12 cells but increased exponentially in 3T3 cells. Cytochrome oxidase and NADH dehydrogenase (nuclear and mitochondrial encoded, cristae location) increased to a lesser extent and with a pattern dissimilar to the first group. Northern blots and activity of succinate dehydrogenase (cristae location but entirely nuclear encoded) suggested the groupings were based on location of the genes rather than the mature enzyme. However, quantitative electron microscopy and comparisons with adult tissue suggested that mitochondrial ultrastructure can influence the change in cristae enzymes. Cristae surface area per unit mitochondrial volume and per unit cell volume increased much less than did cristae enzymes. Available space on the inner membrane may become limiting and account for some aspects of the pattern of change in electron transport enzymes during differentiation.

3T3 Cells↗
PubMed1991

Alpha-adrenergic regulation of phosphoinositide metabolism and protein kinase C in isolated cardiac myocytes.

alpha 1-Adrenergic regulation of phosphoinositide metabolism and protein kinase C translocation was studied in isolated rat cardiac myocytes. Exposure of [3H]inositol-labeled myocytes to norepinephrine in the presence of propranolol caused a dose-dependent increase in [3H]inositol phosphates. Norepinephrine also increased the level of membrane-associated protein kinase C from approximately 10% of total activity to 18%, with a dose response similar to that for generation of inositol phosphates. Depolarization of myocytes with 30 mM KCl had no effect on inositol phosphates or membrane-associated protein kinase C but potentiated the effect of submaximal norepinephrine on both parameters. The potentiation of protein kinase C translocation was amplified when extracellular Ca2+ was increased to 4 mM, resulting in membrane association of one-third of the total cellular activity. These data show that activation of protein kinase C occurs during alpha 1-adrenergic stimulation of cardiac myocytes and that elevation of intracellular Ca2+ amplifies this effect at least in part through increased phosphoinositide metabolism.

Animals↗
PubMed1987

Mechanisms involved in receptor-mediated changes of intracellular Ca2+ in liver.

Interactions between the different signaling roles of myo-inositol 1,4,5-trisphosphate and 1,2-diacylglycerol, the products of agonist-stimulated phosphatidylinositol 4,5-bisphosphate breakdown, are assessed in isolated rat hepatocytes. Measurements of the kinetics of accumulation of individual [3H]inositol phosphates after the addition of different Ca2+-mobilizing agonists in general support the role of inositol 1,4,5-trisphosphate as the second messenger responsible for release of sequestered intracellular Ca2+. Various agonists, when added at maximal concentrations, however, produce qualitatively and quantitatively different responses, which reflect varying abilities of the agonists to activate phospholipase C. Qualitative differences are revealed by a pronounced biphasic pattern to the Ins(1,4,5)P3 accumulation after vasopressin and phenylephrine stimulation, which is indicative of negative feedback. It is suggested that this effect is mediated by a partial diacylglycerol activation of protein kinase C, which in vitro causes an activation of inositol phosphate 5-phosphatase and hence promotes removal of Ins(1,4,5)P3 to Ins(1,4)P2. An alternative mechanism proposed by Biden and Wollheim (1986) of a secondary Ca2+ activation of Ins(1,4,5)P3 3-kinase is considered less likely as a general mechanism, since highly purified kinase prepared from rat brain shows only an inhibition by Ca2+. Glucagon, 8-Br-cAMP, and EGF induce small increases of Ins(1,4,5)P3 in hepatocytes, together with slower and smaller increases of cytosolic free Ca2+ than those produced by vasopressin or phenylephrine, with Ca2+ being mobilized from the same intracellular pools with each of the agonists. The Ca2+-mobilizing effect of glucagon, therefore, may be entirely due to a cAMP-dependent process, although a direct receptor-mediated activation of phospholipase C, as suggested by Wakelam et al. (1986), remains a possibility. The EGF receptor appears to be coupled to phospholipase C, presumably via a G-protein. It is speculated that the mechanism by which cAMP increases Ins(1,4,5)P3 levels in hepatocytes could either be by phosphorylation and inhibition of inositol phosphate 5-phosphatase or by phosphorylation and facilitation of the coupling between the G-protein and phospholipase C. When protein kinase C is maximally activated by pretreatment of hepatocytes with PMA, the stimulatory effects of phenylephrine, glucagon, 8-Br-cAMP, and EGF on the accumulation of inositol phosphates and increase of cytosolic free Ca2+ are largely inhibited.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Phosphate uptake by kidney epithelial (LLC-PK1) cells.

Phosphate uptake by the cultured kidney epithelial cell (LLC-PK1) was studied. The uptake was Na+ dependent, saturable with respect to phosphate and Na+, and energy dependent. The characteristics of the cell uptake system resembled the properties of phosphate transport in the kidney. Parathyroid hormone, dibutyryl cyclic AMP, and forskolin decreased Na+-dependent phosphate uptake. These agonists did not affect Na+-dependent alpha-methylglucoside uptake. Vasopressin and isoproterenol, which do not affect renal phosphate transport, did not inhibit phosphate uptake by the cell. These findings suggest that the cultured cell system may be a useful experimental model for studies of renal phosphate transport and its regulation.

Adenylyl Cyclases↗