A simulation unit for cardiac arrhythmias

This paper describes an electronic model of the conduction system of the heart, in the form of a simulation unit for cardiac arrhythmias. The basic assumptions made are the existence of two distinct cardiac pacemaking centres, and the possibility of reciprocal interaction between them. Details concerning the construction of the simulation unit are given, and its operation is illustrated by means of a few simple examples of cardiac arrhythmias. The advantages presented by this device for teaching and demonstration of various cardiac arrhythmic patterns are also emphasized.     

The binding and processing of monoclonal human IgG1 by cells of a human macrophage-like cell line (U937)

The goal of these experiments was to assess the relationship between the binding and processing of IgG by Fc-receptor-bearing cells. Cells of the U937 human macrophage-like cell line were incubated with 125I- labeled monomers, dimers, oligomers (composed of 2-4 IgG1 subunits), and HP (heavy polymers composed of 5 or more subunits per polymer) of monoclonal human IgG1 in vitro. Binding was assessed by spinning cells through a layer of phthalate oils. Internalization of IgG1 was assessed by quantitating residual binding to cells after surface-bound IgG was removed by a brief treatment with a solution containing 0.25 M acetic acid and 0.5 M sodium chloride. Catabolism was assessed by measuring the release of radioactive fragments of IgG1, which were not precipitated by 10% trichloroacetic acid. Unstimulated U937 bound about 10,000 molecules per cell of IgG1 monomer, with an equilibrium binding constant (Ka) of 5 X 10(8) M-1. After stimulation with a conditioned medium in vitro, binding per cell was increased 3-7--fold, and the Ka was decreased 2-4--fold. Both unstimulated and stimulated cells internalized and catabolized labeled IgG1 HP, but stimulated cells internalized and digested much more IgG1 HP per cell than unstimulated cells. Both monomers and dimers of IgG1 were internalized and degraded very slowly by stimulated cells, even though both preparations readily bound to cells. In contrast, oligomers and (to an even greater extent) IgG1 HP were internalized and degraded much more rapidly. Internalization of IgG1 HP was markedly inhibited by incubation at 4 degrees C, but not by incubation with a variety of metabolic inhibitors. Catabolism was inhibited by chloroquine and monensin (inhibitors of lysosomal acidification) and by cytochalasin (an inhibitor of microfilament polymerization). Binding to the surface of cells was not markedly inhibited by any agent tested. The capacity of cells to bind labeled IgG1 was markedly reduced by prior incubation in the presence of unlabeled IgG1. This reduction was in part due to the steric blockade of receptors caused by the avid, but reversible, binding of IgG1. In addition, IgG1 oligomers or HP (but not IgG1 monomers or dimers) also caused an irreversible reduction in the number of Fc receptors by a process analogous to receptor down-regulation, as observed in other receptor--ligand systems.     

Possibility of selection against mtDNA mutations in tumors

Several studies of tumors have revealed substantial numbers of clonally expanded somatic mutations in mitochondrial DNA (mtDNA), not observed in adjacent intact tissues. These findings were interpreted as indicating the involvement of mtDNA mutations in tumorigenesis. Such comparisons, however, ignore an important confounding factor: the monoclonal origin of tumors as opposed to the highly polyclonal nature of normal tissues. Analysis of recently published data on the incidence of somatic mutations in nontumor monoclonal cells suggests that, contrary to the prevailing view, the process of tumorigenesis may be accompanied by active selection against detrimental mtDNA mutations.     

Comparison of caloric and nutrient intake of adults during week and week-end days

Three-day food records in 174 women and 185 men were used to compare caloric and nutrient intake of week and week-end days. Both women and men were found to consume significantly more energy and a higher level of alcohol during the week-end days than during the week days. In women, a significant decrease in calcium intake was observed during the week-end days in the 36–40 and the 41–45 age groups, respectively. In general, the significant increase in energy intake did not correspond to a significant increase in other nutrients.     

Biochemical properties and kinetic parameters of monoamine oxydase in human seminal plasma

The present study demonstrates that monoamine oxydase (MAO) is present in the human seminal plasma and that its activity was higher in infertile than in fertile men. The Km and Vmax of the enzyme were, respectively, 3.0 X 10(-3) M and 625 eta mol of deaminated 5-HT mg of prot-1 min-1. The enzyme was activated by pyridoxal-5' phosphate but inhibited by usual MAO inhibitors such as pargyline-HCl, iproniazid-PO4 and clorgyline. These findings suggest a relationship between the synthesis and degradation of biogenic amines and testicular function.