Physical chemical studies of short-chain lecithin homologues. II. Micellar weights of dihexanoyl- and diheptanoyllecithin

The micellar weights of dihexanoyl- and diheptanoyllecithin in aqueous solutions are calculated from light scattering and ultracentrifugation data. A monomer-micelle assocation model is used and corrections for the thermodynamic nonideality, on the basis of rigid noninteracting particles, are applied. A few experiments on the influence of high NaCI concentrations (up to 3 M) are described. Dihexanoyllecithin forms micelles with micellar weight of 15 000 to 20 000 and with rather narrow weight distributions. Diheptanoyllecithin micelles however, have broad size distributions with micellar weights of 20 000 up to about 100 000 in the concentration range studied. Micelles are assumed to be spherical or to have sphero-cylindrical shapes depending on the molecular weights. Two models are used: (1) a compact structure, where no attention is paid to the hydrocarbon-water contact (2) micelles with as little hydrocarbon-water contact as possible.     

On catecholamine-containing cells in the rat interatrial septum

Summary The interatrial septum of the rat heart contains cells which show a strong intensive-yellow paraformaldehyde-induced fluorescence. By electron microscopy these cells are characterized by an abundance of dense-core vesicles.Cholinergio axons form axo-somatic synaptic contacts with the catecholamine-containing cells. These cells, packed with dense-core vesicles, are frequently interdigitated and interconnected by zonulae and maculae adhaerentes and occludentes. The catecholamine-containing cells are surrounded by satellite cells either individually or in groups.The catecholamine-containing cells, which bear blunt, plumpish processes, can be subdivided, on the basis of position and morphology into two types. One class of cells lies within the fibroblast capsule of the intra-atrial ganglion (van der Zypen, Hasselhorst, Merz and Fillinger, 1974). A second aggregation of catecholamine-containing cells occurs outside the ganglia in close proximity to capillaries. The capillaries exhibit pores in the area of contact with the catecholaminergic cells. The structure of these catecholamine-containing cells is described and their possible function discussed.

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Zusammenfassung Im Septum interatriale des Rattenherzens treten Zellen in Erscheinung, die nach Paraformaldehyd-Bedampfung eine intensive hellgelbliche Fluoreszenz zeigen. Diese Zellen zeichnen sich durch einen großen Reichtum an dense-core vesicles aus. Cholinerge Axone bilden axo-somatische Synapsen an den katecholaminhaltigen Zellen aus. Die mit dense-core vesicles angefüllten Zellen sind oft ineinander verzahnt und durch Zonulae adhaerentes verbunden. Einzeln oder in Gruppen werden die katecholamin-enthaltenden Zellen von Satelliten-Zellen umgeben.Die mit kurzen plumpen Fortsätzen versehenen katecholaminhaltigen Zellen lassen aufgrund ihrer Lage und eines andersartigen Baues zwei Typen erkennen. Eine Gruppe von Zellen liegt innerhalb der Fibrozytenkapsel des Ganglion intraatriale (van der Zypen, Hasselhorst, Merz und Fillinger, 1974). Eine zweite Ansammlung von Katecholamin enthaltenden Zellen findet sich außerhalb der Ganglien in engem Kontakt zu Kapillaren. Die Kapillaren weisen im Bereich des Kontaktes mit den katecholaminergen Zellen Poren auf. Die Struktur dieser Zellen wird geschildert und ihre mögliche Funktion diskutiert.

     

Phase shifts in heterochromatic flicker photometry and Bidwell's ghost: A model

A simple model of brightness encoding in the retina is proposed that explains:

1. the differential phase shift needed to minimize brightness flicker in a homogeneous red-green counterphase flickering field.
2. the modulation transfer function at low temporal frequencies for flickering lights of one dominant wavelength against the background of light with another dominant wavelength.
3. the occurrence of the Hering, the Purkinje and the Hess afterimages.
4. the ability of monochromatic light to provoke the Purkinje afterimage (Bidwell's ghost).

It is shown that these effects can be treated as pure brightness effects; or that the signal processing of the opponent system is irrelevant to the results. A physiological substrate for the model is tentatively indicated. Some suggestions are made concerning possible experimental checks of the model.     

High-resolution scanning-densitometry of photographic negatives of human metaphase chromosomes

Summary In photomicrographic negatives of cytochemically stained human metaphase preparations, images of individual chromosomes were scanned interactively with a Zeiss SMP interfaced to a PDP-12 computer.By means of the CHROSCAN computer program spot-scanning of selected chromosomes was performed in a direction perpendicular to the length axis, each measured value being corrected for background absorbance taken on both sides of the chromosome image. Plotting of the integrated absorbance values of each transversal scanline results in a graphic representation of the absorbance distribution over the chromsome length. Following this procedure, longitudinal curves were obtained which showed the characteristic patterns obtained after Q or G banding, and, in the case of Feulgen-staining, represented quantitative variations of DNA mass along the individual chromosomes. For Feulgen-stained chromosomes, the total integrated absorbance value and the ratio of integrated absorbance in the long arm over the total integrated absorbance, correspond with the DNA-absorbance and-arm ratio values per chromosome respectively.The results of investigations concerning the reproducibility and accuracy of cytochemical Feulgen staining and of the photographic procedures are presented, together with total integrated Feulgen-DNA absorbance and arm ratio values for a number of human chromosomes.For several chromosomes, Feulgen absorbance arm ratio measurements were found to result in values more constant over different metaphases when the long arm was considered to start at the lowest dip in the longitudinal absorbance curve, than when the microscopically observable primary constriction was taken to represent the centromere. The results indicate that the present method allows accurate photometry of naturally absorbing, or of stained or fluorescent objects, with measuring intervals of 0.16 . In addition it is shown that the arm ratio values and total DNA content can serve as very constant parameters for karyotype analysis.Supported by grant nr. 28-16915 of the Praeventiefonds, 's Gravenhage.