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Biomedical subjects

F Franks

Publications and source records attributed to F Franks.

44 records · Page 3Linked to original sources
PubMed1977

Polymeric cryoprotectants in the preservation of biological ultrastructure. II. Physiological effects.

A study has been made of the physiological effects of three non-penetrating polymeric cryoprotective agents on sixteen different plant and animal cells and tissues. The cryoprotectants, when used at concentrations at which they are effective in preventing ice-crystal formation, generally have a lower toxicity to cells and tissue than similar concentrations of glycerol. The relatively low toxicity of these substances suggests that they would be more suitable as cryoprotectants for morphological and analytical studies than the commonly used low molecular weight compounds.

Cell Survival↗
PubMed1977

Polymeric cryoprotectants in the preservation of biological ultrastructure. III. Morphological aspects.

Two high molecular weight polymers, polyvinylpyrrolidone (PVP) and hydroxyethyl starch (HES), have been used as cryoprotectants for preparing specimens to be freeze fractured. Solutions of 25% (w/w) suppress the formation of intracellular ice in single cells and tissue blocks from both plants and animals to the extent that fine structural details of the cell can be elucidates. The mode of action of these cryoprotectants, together with the structures they reveal and the peculiar advantages attached to their use, is discussed.

Cryoprotective Agents↗
PubMed1977

Biological freezing and cryofixation.

Freezing and freeze fixation are commonly used to achieve ultrastructural and biological preservation. Freezing in biological materials is complex because of their heterogeneous nature-water is unevenly distributed and the various domains are separated by semi-permeable membranes. Processes to be considered include: (1) osmotic gradients leading to redistribution of water, (2) nucleation and uncontrolled growth of ice crystals, (3) recrystallization of nucleated aqueous substrate. To avoid ultrastructural deformation in biological specimens cryofixatives are commonly employed. These are water soluble molecules, able to penetrate cell membranes (e.g. glycerol and dimethylsulphoxide). Interacting strongly with water, ions and bipolymers, they give rise to metabolic and physiological changes which render them useless for X-ray microprobe analytical studies. However, they can enable tissues to survive low temperature storage. Some plants and animals develop in vivo mechanisms which enable them to avoid or tolerate freezing. Alternative means of cryofixation have recently been developed. They rely on non-penetrating polymers of high and specific water binding capacity. These polymers enable the extracellular spaces to be vitrified rather than frozen. Such suppression of ice nuclei enables the cell contents to be maximally subcooled, resulting in the formation of nm dimension ice crystals. Since the polymers have a low osmotic activity and do not penetrate membranes, the interior of the cell is substantially undisturbed. Also hydrophilic polymers used as cryofixatives are physiologically less active than conventional cryoprotectants at equivalent weight concentrations, and th eir mechanical properties render them useful as matrices for cryosectioning.

Cytological Techniques↗
PubMed1971

Specificity of some ganglion stimulants.

1. The specificity of several ganglion stimulants has been tested on the isolated guinea-pig ileum by measuring the dose ratios produced by concentrations of hexamethonium.2. Most ganglion stimulants are also active at postganglionic receptors, some as blocking agents (for example, lobeline and dimethylphenylpiperazinium), others as agonists (for example, o-aminophenethyltrimethylammonium and, to a lesser extent, nicotine). The most specific ganglion stimulant, with the least activity at postganglionic receptors, was p-aminophenethyltrimethylammonium.3. The affinity constants of lobeline and dimethylphenylpiperazinium for the muscarine sensitive receptors in the guinea-pig ileum are 1.05 x 10(6) and 3.71 x 10(4), respectively.4. The antagonism of p-aminophenethyltrimethylammonium by hexamethonium gave results consistent with competition up to dose ratios of about 20. Such results could also be obtained if the antagonism were non-competitive, however, provided large responses could be obtained with less than about 5% of the receptors in the ganglia activated. The affinity constant of hexamethonium is about 2.6 x 10(5).5. It is suggested that the affinity of hexamethonium can largely be ascribed to hydrophobic bonding.

Animals↗