Dcytb has been identified as the mammalian transplasma ferric reductase that catalyzes the reduction of ferric to ferrous iron in the process of iron absorption. Its mRNA and protein levels are up-regulated by several independent stimulators of iron absorption. Furthermore, its cDNA encodes putative binding sites for heme and ascorbic acid. Using Northern and Western blots, RT-PCR and confocal microscopy, we studied the expression and localisation of Dcytb in cell lines and tissues of CD1 mice. Dcytb expression and function were modulated by iron. Dcytb and DMT1, both predominantly localised in the apical region of the duodenum were up-regulated in iron deficiency. Dcytb, the iron regulated ferric reductase may also utilize cytoplasmic ascorbate as electron donor for transmembrane reduction of iron. Dcytb expression was found in other tissues apart from the duodenum and its regulation and functions at these other sites are of interest in iron metabolism.

Ascorbic Acid↗

PubMedDate not supplied

Ferric iron reduction and iron assimilation in Saccharomyces cerevisiae.

We have used the yeast Saccharomyces cerevisiae as a model organism to study the role of ferric iron reduction in eucaryotic iron uptake. S. cerevisiae is able to utilize ferric chelates as an iron source by reducing the ferric iron to the ferrous form, which is subsequently internalized by the cells. A gene (FRE1) was identified which encodes a protein required for both ferric iron reduction and efficient ferric iron assimilation, thus linking these two activities. The predicted FRE1 protein appears to be a membrane protein and shows homology to the beta-subunit of the human respiratory burst oxidase. These data suggest that FRE1 is a structural component of the ferric reductase. Subcellular fractionation studies showed that the ferric reductase activity of isolated plasma membranes did not reflect the activity of the intact cells, implying that cellular integrity was necessary for function of the major S. cerevisiae ferric reductase. An NADPH-dependent plasma membrane ferric reductase was partially purified from plasma membranes. Preliminary evidence suggests that the cell surface ferric reductase may, in addition to mediating cellular iron uptake, help modulate the intracellular redox potential of the yeast cell.

Cell Membrane↗

PubMedDate not supplied

Damage in canine hearts following defibrillator shocks.

Experiments were performed to investigate possible differences in potential myocardial cell damage following the use of two clinically available difibrillators. One had a damped sine wave (DSW), and the other a truncated exponential waveform (TEW). The latter, therefore, had a lower peak current and voltage. After pilot studies to determine damage potential, an energy content of 10 Joules per kg was selected with three transthoracic shocks at 30 second intervals, delivered with paddles, by both defibrillators. Thirteen dogs were shocked with DSW (10 sacrificed at 24 hours and three at 72 hours). Eleven dogs were shocked with TEW (eight sacrificed at 24 hours and three at 72 hours). Three were used as untreated controls. Observations included ECG monitoring, technetium99m pyrophosphate (Tc-PyP) uptake, and gross and microscopic observations including electron microscopy. This report will concentrate on the morphologic changes. Eleven of 13 dogs shocked with DSW developed ventricular tachycardia, transient heart block, Tc-PyP uptake and myocardial cell death with acute necrosis, and aberrant contraction patterns associated with cell death. Progression of the lesions occurred from 24 to 72 hours. Only two (one at 24 hours and one at 72 hours) of the dogs shocked with TEW showed microscopic foci of necrosis. One was a chance finding (24 hours); the other was associated with an overlying "yellow streak". In neither case were arrhythmias or Tc-PyP uptake observed. The results indicate that in dogs at equivalent energy levels, TEW caused significantly less myocardial damage than DSW.

Animals↗