Precipitation of calcium palmitate from bile salt-containing dispersions.

Addition of calcium chloride to mixed micellar systems composed of sodium salts of palmitic acid and high concentrations of different bile acids results in precipitation of Ca(palmitate)2 only when the palmitate concentration exceeds a critical value, which is dependent on the concentrations of Ca2+, Na+ and bile salt, and on the type of bile salt used. All these dependencies, as well as the complex and interrelated effects of the various parameters on the kinetics of Ca(palmitate)2 precipitation are consistent with the following mechanism: (i) calcium binds to palmitate-bile salt mixed micelles and promotes their aggregation, at a rate governed by the concentration ratio between bound calcium and micelles (here denoted "binding ratio"). (ii) Ca(palmitate)2 precipitation occurs within the aggregate of micelles only if those micelles include sufficient amounts of Ca2+ and palmitate to allow for the formation of large enough crystal units of Ca(palmitate)2 which can serve as nucleation "seeds". Both the concentrations of micelles and Na+ have dual effects on the rate of precipitation. Increasing micelle concentration, by itself, accelerates aggregation but at the same time leads to a decrease of the binding ratio, thus reducing the rate of precipitation. Na+ which reduces the binding ratio through competitive binding also reduces the surface charge, thus assisting micelle aggregation. Our model also explains the facilitation of precipitation observed when phosphatidylcholine is contained in the palmitate-bile salt mixed micelles and the inhibitory effect of the water soluble bovine serum albumin.

Visual acuity tests using chart, line, and single optotype in healthy and amblyopic children.

PURPOSE: The purpose of this study was to evaluate the difference between full chart, single line, and single optotypes visual acuity (VA) test results in healthy and amblyopic children. METHODS: Thirty-five children with amblyopia (20 with strabismus and 15 with anisometropia) and 40 ophthalmologically normal age-matched children were examined. The mean age of the patients in the study and control groups did not differ significantly (P= .9). A commercial projector that projected tumbling-E randomly placed optotypes was used. The VA of the amblyopic eye of the patients in the study group and the right eye of the patients in the control group was examined first using a full chart of optotypes, then using a single line of optotypes, and finally with individual symbols. The procedure was repeated with the other eye. RESULTS: LogMAR VA improved when the full chart was substituted with a single line, and improved by a similar increment further with single optotypes, in both the study and control groups. VA improved significantly more in eyes with amblyopia than in control subjects. Results were not influenced by age. CONCLUSION: VA testing using a single line gives better, sometimes misleading results, than tests with a full chart because it reduces but does not eliminate the crowding effect. When using a device that can employ more than 1 mode, the exacttest mode should be specified and maintained throughout the follow-up.

Anatomical and ultrastructural changes in aleurone and myrosin cells of Sinapis alba during germination.

The cells of the embryo of Sinapis alba L. include either aleurone or myrosin grains and all cells contain oil bodies. Aleurone grains and oil bodies are degraded during germination. The myrosin grains of each myrosin cell, on the other hand, gradually turn into one big vacuole containing the myrosin. Probably very little, if any, new myrosin is formed in the cotyledons and hypocotyl of the seedling after germination. No difference was found between aleurone and myrosin cells in the development of organelles. The cells of provascular bundles of the mature embryo contain different amounts of aleurone grains in different stages of development, and their organelles are more developed than those of all other cells.