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Biomedical subjects

A Watts

Publications and source records attributed to A Watts.

At least 217 records · Page 12Linked to original sources
PubMed1979

Simple metallic compounds as pulp-capping agents.

A study is described in which six metallic compounds identified in a previous pilot experiment were tested as pulp-capping agents using the exposed rat molar. Barium sulfate, calcium carbonate, cupric oxide, ferric oxide, and heavy magnesium oxide gave poor results. Stannic oxide gave more favorable results and is being studied further.

Animals↗
PubMed1977

Cooperativity of the phase transition in single- and multibilayer lipid vesicles.

The effect of membrane morphology on the cooperativity of the ordered-fluid, lipid phase transition has been investigated by comparing the transition widths in extended, multibilayer dispersons of dimyristoyl phosphatidyl-choline, and also of dipalmitoyl phosphatidylcholine, with those in the small, single-bilayer vesicles obtained by sonication. The electron spin resonance spectra of three different spin-labelled probes, 2,2,6,6-tetramethylpiperdine-N-oxyl, phosphatidylcholine and stearic acid, and also 90 degrees light scattering and optical turbidity measurements were used as indicators of the phase transition. In all cases the transition was broader in the single-bilayer vesicles than in the multibilayer dispersions, corresponding to a decreased cooperativity on going to the small vesicles. Comparison of the light scattering properties of centrifuged and uncentrifuged, sonicated vesicles suggests that these are particularly sensitive to the presence of intermediate-size particles, and thus the spin label measurements are likely to give a more reliable measure of the degree of cooperativity of the small, single-bilayer vesicles. Application of the Zimm and Bragg theory ((1959) J. Chem. Phys. 31, 526-535) of cooperative transitions to the two-dimensional bilayer system shows that the size of the cooperative unit, 1/square root sigma, is a measure of the mean number of molecules per perimeter molecule, in a given region of ordered or fluid lipid at the centre of the transition. From this result it is found that it is the vesicle size which limits the cooperativity of the transition in the small, single-bilayer vesicles. The implications for the effect of membrane structure and morphology on the cooperativity of phase transitions in biological membranes, and for the possibility of achieving lateral communication in the plane of the membrane, are discussed.

Chemical Phenomena↗
PubMed1977

Simple metallic compounds as pulp-capping agents. A pilot study.

A pilot study is described in which the exposed pulps of molar teeth of normal laboratory rats were capped with various metallic compounds in general medical usage. There appeared to be no relationship between the response obtained and the pH of the compounds studied. Aluminum powder, aluminum hydroxide, Aludrox, aluminum oxide, light magnesium oxide, magnesium hydroxide, and titanium dioxide gave poor results. Barium sulfate, calcium carbonate, cupric oxide, ferric oxide, heavy magnesium oxide, and stannic oxide merited more detailed study.

Animals↗
PubMed1976

Evidence for phase boundary lipid. Permeability of Tempo-choline into dimyristoylphosphatidylcholine vesicles at the phase transition.

The existence of distinct regions of mismatch in molecular packing at the interfaces of the fluid and ordered domains during the phase transition of dimyristoylphosphatidylcholine vesicles has been demonstrated by measuring the temperature dependence of the permeability to a spin-label cation and comparing this with a statistical mechanical calculation of the fraction of interfacial lipid. The kinetics of uptake and release of the 2,2,6,6-tetramethylpiperidinyl-1-oxycholine (Tempo-choline) spin label by single-bilayer dimyristoylphosphatidylcholine vesicles were measured using electron spin resonance spectroscopy to quantitate the amount of spin label present within the vesicles after removal of the external spin-label by ascorbate at 0 degrees C. Both the uptake and release experiments show that the Tempo-choline permeability peaks to a sharp maximum at the lipid-phase transition, the vesicles being almost impermeable to Tempo-choline below the transition and having a much reduced permeability above. The temperature profile of the permeability is in reasonable quantitative agreement with calculations of the fraction of interfacial boundary lipid from the Zimm and Bragg theory of cooperative transitions, which use independent spin-label measurements of the degree of transition to determine the cooperativity parameter. The relatively high intrinsic permeability of the interfacial regions (P approximately 0.2-1.0 X 10(-8) cm/s) is attributed to the mismatch in molecular packing of the lipid molecules at the ordered-fluid boundaries, which could have important implications not only for permeability in natural membranes (e.g., in transmitter release), but also for the function of membrane-bound enzymes and transport proteins.

Binding Sites↗