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Biomedical subjects

M Chamberlin

Publications and source records attributed to M Chamberlin.

At least 19 recordsLinked to original sources
PubMed2006

Glucose and diabetes: effects on podocyte and glomerular p38MAPK, heat shock protein 25, and actin cytoskeleton.

Phosphorylated p38 (pp38) mitogen-activated protein kinase (MAPK) regulates heat shock protein 25 (HSP25), stabilizing fibrillar actin (FA) and preventing cleavage to G-actin (GA). Cultured podocytes (Pods) were exposed to glucose (5.5-50 mM)+/-p38MAPK inhibitor SB202190 (SB) or control SB202474 to assess the effects on FA/GA and Pod structure. The relationship of p38MAPK with in vivo Pod structure and albuminuria (Ualb) was assessed in rats with streptozotocin (SZ)-induced diabetes (DM) for 1 week, 1 month, and 4 months. High glucose induced concentration-dependent increases in pp38MAPK and phosphorylated HSP25 (pHSP25) maintained actin cytoskeleton. Inhibition by SB diminished pp38MAPK and pHSP25, decreased FA/GA, and altered FA and GA immunohistochemical appearance. In SZ-DM, glomerular pp38MAPK and biphosphorylated HSP25 were increased after 1 week, declining at 1 month, and at or below C values at 4 months. Glomerular FA/GA in DM was normal at 1 week, declining at 1 month, and low at 4 months. Ualb/creatinine was similar in DM vs C at 1 week, and increased at 1 and 4 months. Morphometry demonstrated progressively diminishing slit pore density in DM over time, denoting evolving effacement. There were strong correlations between slit membrane density and both glomerular biphosphorylated HSP25 and ln Ualb/cr ratio. The data suggest that increased pp38MAPK and pHSP25 comprise an acute adaptation to glycemic stress. Later depletion of DM may contribute to Pod structural alterations and Ualb.

Actins↗
PubMed1998

Engineering secondary metabolism in maize cells by ectopic expression of transcription factors.

Manipulation of plant natural product biosynthesis through genetic engineering is an attractive but technically challenging goal. Here, we demonstrate that different secondary metabolites can be produced in cultured maize cells by ectopic expression of the appropriate regulatory genes. Cell lines engineered to express the maize transcriptional activators C1 and R accumulate two cyanidin derivatives, which are similar to the predominant anthocyanin found in differentiated plant tissues. In contrast, cell lines that express P accumulate various 3-deoxy flavonoids. Unexpectedly, P-expressing cells in culture also accumulate phenylpropanoids and green fluorescent compounds that are targeted to different subcellular compartments. Two endogenous biosynthetic genes (c2 and a1, encoding chalcone synthase and flavanone/dihydroflavonol reductase, respectively) are independently activated by ectopic expression of either P or C1/R, and there is a dose-response relationship between the transcript level of P and the degree to which c2 or a1 is expressed. Our results support a simple model showing how the gene encoding P may act as a quantitative trait locus controlling insecticidal C-glycosyl flavone level in maize silks, and they suggest how p1 might confer a selective advantage against insect predation in maize.

Journal Article↗
PubMed1997

Mitochondrial arginine kinase in the midgut of the tobacco hornworm (Manduca sexta)

Mitochondria isolated from the posterior midgut of the tobacco hornworm (Manduca sexta) contain arginine kinase. The distribution of mitochondrial and cytoplasmic marker enzymes indicates that the presence of mitochondrial arginine kinase is not due to cytoplasmic contamination. Arginine is not oxidized by the midgut mitochondria but, when metabolic substrates and ATP are present, respiration can be initiated by the addition of arginine. Under these conditions, there is no return to State 4 respiration, indicating regeneration of ADP by the arginine kinase reaction. Respiration can be blocked, however, by atractyloside, an inhibitor of the adenine nucleotide translocator. These results indicate that arginine kinase resides outside the matrix. Mitochondrial arginine kinase is specific to l-arginine since analogs of l-arginine are ineffective in stimulating respiration in the presence of ATP. Coupling between the adenine nucleotide translocator and arginine kinase was investigated using kinetic and thermodynamic approaches. There were no differences in the activities of arginine kinase in respiring and non-respiring mitochondria when they were measured at different ATP or arginine concentrations. This result indicates that arginine kinase does not have preferential access to the ATP exported out of the matix. A comparison of the apparent equilibrium constant and the mass action ratio of the arginine kinase reaction also confirms that there is no microcompartmentation of the reaction.

Journal Article↗
PubMed1997

Changes in midgut active ion transport and metabolism during larval-larval molting in the tobacco hornworm (Manduca sexta)

Ion transport and metabolism in the posterior midgut before, during and after the molt to the fifth instar of the tobacco hornworm Manduca sexta were investigated. In situ measurements reveal that the transepithelial potential difference of the posterior midgut falls during the molting process. This finding was confirmed by in vitro experiments in which it was demonstrated that both the transepithelial potential and the short-circuit current are lower in molting fourth instars compared with feeding fourth instars. The short-circuit current increases after ecdysis, with a maximal rate being achieved approximately 4 h after the molt. Resumption of feeding after the molt is not necessary to initiate this increase in active ion transport. The metabolic organization of the tissue also changes during the molting process. The maximal activities of glycolytic enzymes and 3-hydroxyacyl-CoA dehydrogenase, an enzyme of lipid ss-oxidation, decrease during the molting process and increase after ecdysis. Although citrate synthase activity, an index of maximal aerobic capacity, decreases during the molt and increases again after ecdysis, tissue respiration is the same in feeding fourth instars and molting larvae. This result indicates that a greater percentage of maximal aerobic capacity is used during molting and that energy may be diverted to cell proliferation and differentiation and away from the support of active ion transport at this time.

Journal Article↗
PubMed1996

Interactions of the RecBCD enzyme from Escherichia coli and its subunits with DNA, elucidated from the kinetics of ATP and DNA hydrolysis with oligothymidine substrates.

Oligothymidines eight nucleotides or longer stimulate ATP hydrolysis by the RecBC and RecBCD enzymes, and they are substrates for the ATP-stimulated nuclease activity of RecBCD. The steady-state kinetics of ATP hydrolysis by the RecBC enzyme are consistent with a single ATPase and DNA binding site. Results with RecBCD and RecBCD-K177Q [an enzyme with a Lys-to-Gln mutation in the ATP binding motif of the RecD subunit [Korangy, F., & Julin, D. A. (1992) J. Biol. Chem. 267, 1727-1732]] indicate that ATP hydrolysis by the RecB subunit is stimulated by pd(T)12 binding to a high-affinity site, while the RecD subunit hydrolyzes ATP stimulated by pd(T)12 binding to a low-affinity site. The site which stimulates RecB has about 50-fold greater affinity for DNA in either RecBCD or RecBCD-K177Q than does the corresponding site in RecBC. The rates of ATP hydrolysis observed for the RecBCD enzyme at low concentrations of pd(T)12 are best explained by a mechanism where the enzyme binds to the DNA and catalyzes multiple rounds of ATP hydrolysis before dissociating. Larger DNA molecules [pd(T)25-30 and poly(dT)] are bound more tightly by RecBCD, are hydrolyzed more rapidly, and are much more effective in stimulating ATP hydrolysis than is pd(T)12. The results at low ATP concentrations where the nuclease activity is minimal (5 microM) suggest that ATP hydrolysis is stimulated by the DNA ends, but there is no evidence that the RecBCD enzyme moves along these DNA molecules in an ATP-dependent manner under these conditions.

Adenosine Triphosphatases↗
PubMed1990

Trends in congenital heart disease in Dallas County births. 1971-1984.

To examine the changes in birth cohort prevalence rates and severity of congenital heart disease, we studied children with congenital heart disease born to blacks, whites, and Mexican-Americans in Dallas County from 1971 through 1984. Diagnoses were made by pediatric cardiologists' clinical evaluations, echocardiography, catheterization, surgery, or autopsy. During this study period, 2,509 of 379,561 liveborn infants were diagnosed, a prevalence rate of 6.6/1000. The rates for whites was significantly higher than for blacks or Mexican-Americans--7.2/1,000, 5.6/1,000, and 5.9/1,000, respectively. The rate for severe cases requiring cardiac catheterization or surgery or undergoing autopsy was 3.1/1,000 and did not differ among the three groups. The time trend for rates of congenital heart disease suggested an apparent increase in prevalence rate during the 1970s; however, the prevalence rate of severe forms remained relatively stable. This indicates that the apparent rise in prevalence could be accounted for by an increase in detection of mild cases. These findings were interpreted as reflecting a greater tendency for pediatricians to refer asymptomatic children with significant heart murmurs to a pediatric cardiologist.

Black People↗
PubMed1988

Some major transport mechanisms of insect absorptive epithelia.

1. After hormonal stimulation, fluid reabsorption (JV) in locust hindgut from the KCl-rich, low-Na primary urine is driven primarily by an unusual mucosal electrogenic Cl- pump (JCl). 2. Cyclic-AMP increases JCl and also mucosal K+ and basolateral Cl- conductances, so that KCl absorption exceeds that of Na+ in rectum but not ileum. 3. Mucosal entry of Na+ occurs by exchange for NH4+ (H+), by cotransport with some neutral amino acids, and through putative channels. 4. However, transport of proline, the predominant organic substrate, is largely Na-independent and drives a sizable component of Jv in rectal but not ileal segments. 5. There is evidence for hormonal control of Na+ reabsorption in ileum but not rectum.

Absorption↗
PubMed1978

Augmented peritoneal mass transport with intraperitoneal nitroprusside.

Lightly restrained, alert New Zealand white rabbits underwent peritoneal dialysis by percutaneous instillation of standard dialysis solution with or without intraperitoneal nitroprusside. Corrected to a mean intraperitoneal dwell time of 36 minutes, mean clearances of creatinine and urea were 0.74 and 0.90 ml/kg/min in six rabbits. With intraperitoneal nitroprusside, 1.13 mg/kg clearances increased to 1.13 and 1.30 ml/kg/min (p less than 0.01) respectively. The 53% increment in creatinine clearance maintained the ratio clearance larger/smaller solute suggesting increased peritoneal permeability and/or area. Lower nitroprusside doses were less effective and not significantly above control. Nitroprusside also increased clearances during hypertonic peritoneal dialysis, but had no effect on osmotically induced water flux. Lavage studies demonstrated a persistent effect of nitroprusside after a single exposure and a sustained effect with repeated use.

Animals↗
PubMed1977

Isolation of recombinants between T7 and T3 bacteriophages and their use in vitro transcriptional mapping.

A variety of T3 X T7 recombinants were isolated from crosses between T3 and T7 parental phages carrying amber markers in various genes (gene 1 to gene 19). The genetic constitution of these recombinants was determined by reference to the selected markers and also directly by analysis of the proteins translated from the T3 X T7 recombinants in vivo. Although T3 and TM phages are closely related, most T3 and T7 proteins differ slightly in size, and hence the genetic origin of a gene can be determined by protein analysis. The major transcripts read by T3 and T7 RNA polymerases from T3 X T7 recombinant phage DNAs vary, depending on which regions of the T3 or T7 chromosome are present. T7 RNA polymerase is unable to utilize major promoter sites employed by T3 polymerase at an appreciable rate, and the converse is also true. Hence the transcriptional pattern for a recombinant phage DNA obtained with the T3 or T7 polymerase allows a determination of the identity of the different promoter sites on the genome. The transcriptional analysis of T3 X T7 recombinant DNAs together with earlier observations has been used to map the promoter sites for five out of seven major T3 and T7 RNA species on the genetic maps of T3 and T7. The promoter sites for the T7 and T3 RNA species IIIa, IV, and V originate at the beginning of genes 7, 9, and 10, respectively; the promoter sites for the T7 and T3 RNA species I and II are located to the left of gene 11 and gene 13, respectively. No T3 X T7 recombinants were found for which the specificity of the phage RNA polymerase was not correlated with the corresponding promoter sites for species IIIa and I (the transcription of which covers 60% of the genome). That means that the RNA polymerase specified by the recombinant genome is able to read all of the information encoded in sequences read normally from major promoters by the enzyme on the wild-type phage genome. This suggests that the in vitro specificity for promoter site selection by the phage polymerases is also maintained in vivo.

Coliphages↗
PubMed1974

A preliminary map of the major transcription units read by T7 RNA polymerase on the T7 and T3 bacteriophage chromosomes.

Transcription of T7 DNA by T7 RNA polymerase in vitro gives rise to six major size classes of RNAs comprising seven major T7 RNA species. These RNAs are all read from the r-strand of T7 DNA and are not derived from the early (leftmost on the conventional genetic map) region of the molecule. When artifically shortened T7 DNA templates are transcribed, four (I, II, IIIb, and VI) of the seven species are found to be truncated or deleted. This indicates that all are terminated near the right end of the T7 DNA molecule, probably at a common termination site near 98.5%. (Map positions are all given in terms of percentage of total length measured from the left end of the molecule.) Since the approximate lengths of the transcripts are known, the promotor sites for T7 RNA species I, II, IIIb, and VI are tentatively mapped at 56, 64, 83, and 97% on the T7 chromosome. Only a single major T3 RNA is transcribed by T7 RNA polymerase; analysis of transcripts directed by shortened T3 DNA templates indicates it is analogous to T7 RNA species IIIb. Hence the promotor and terminator sites for T3 species IIIb are tentatively mapped at 83 and 98.5%, respectively, on the T3 chromosome. The major transcripts read by T7 RNA polymerase from T3-T7 hybrid phage DNAs vary, depending on which regions of the T7 chromosome are present. This provides an alternative method of mapping the strong T7 promotor sites on the T7 chromosome.

Chromosome Mapping↗
PubMed1974

Isolation and characterization of prototrophic mutants of Escherichia coli unable to support the intracellular growth of T7.

Mutants of E. coli B/1 were isolated which grew normally but did not permit the intracellular growth of bacteriophage T7. Two classes of mutants were studied in detail (tsnB(-) and tsnC(-)). These strains adsorbed T7 normally and were killed by the infection. Synthesis of T7 RNA and of early and late classes of T7 proteins occurred normally after infection. In T7-infected tsnB(-) cells, T7 DNA synthesis stopped prematurely shortly after its onset, suggesting that the tsnB function affects a step in the late phase of T7 DNA replication. Mutants of T7 were isolated (T7beta) which could grow on tsnB(-) cells. In T7-infected tsnC(-) cells, T7 DNA synthesis was completely blocked, suggesting that the tsnC function affects a step in an early phase of T7 DNA replication.

Coliphages↗