Calcium light absorption

At one time calcium ions seemed to be the logical internal messenger between rhodopsin and the plasma membrane. If light absorption opened channels from the internal space of the rod discs, calcium ions could be released and diffuse quickly to the plasma membrane and block the entrance of sodium ions. However, light does not increase the free [Ca " "] in the cytoplasm but may decrease it from 500 nM to as low as 50 Stryer suggested that the essential... 

Fluorescent dyes, such as rhodamine B, are useful indicators for the existence of the small reversed micelles formed in solvents of low polarity [17]. Little and Singleterry [18] were the first to explore the special properties of rhodamine B, which, when added to a benzene solution containing low concentrations of calcium 4-phenylaniline stearate, showed a manyfold increase in light absorption and a notable enhancement of fluorescence intensity. 

Elution volume calibrations were performed using radioactive tracers of the rare earth elements and 133Ba, with atomic-absorption or flame-emission analysis of iron, sodium, potassium, calcium, and magnesium. As shown in Fig. 5.14, any barium added to the second columns is eluted at the start of the light rare earth element fraction . To ensure barium removal the sample can be put through the first column again. 

Ultraviolet light causes a chemical change in dihydrocholesterol to produce cholecalciferol, a precursor of vitamin D. The latter conforms better to the definition of a steroid hormone than a vitamin. Indeed, the classification of vitamin D as a vitamin is an historical accident. The precursor is released from the skin and is further modified in the liver and kidney to form dihydroxycholecalciferol, which is the active form of the hormone (see Chapter 15 for the reactions). It increases calcium absorption from the... 

Vitamin D hormone is derived from vitamin D (cholecalciferol). Vitamin D can also be produced in the body it is formed in the skin from dehydrocholesterol during irradiation with UV light. When there is lack of solar radiation, dietary intake becomes essential, cod liver oil being a rich source. Metaboli-cally active vitamin D hormone results from two successive hydroxylations in the liver at position 25 ( calcifediol) and in the kidney at position 1 ( calci-triol = vit. D hormone). 1-Hydroxylation depends on the level of calcium homeostasis and is stimulated by parathormone and a fall in plasma levels of Ca or phosphate. Vit D hormone promotes enteral absorption and renal reabsorption of Ca and phosphate. As a result of the increased Ca + and phosphate concentration in blood, there is an increased tendency for these ions to be deposited in bone in the form of hydroxyapatite crystals. In vit D deficiency, bone mineralization is inadequate (rickets, osteomalacia). Therapeutic Liillmann, Color Atlas of Pharmacology... 

Buffer solution, double strength - add to 4.5 I water, 400 g oven-dried calcium acetate, 80 g 4-nitrophenol and 6 g of light magnesium oxide. [Safety note 4- (or para-) nitrophenol may cause eye irritation or irreversible eye injury, and may be harmful by absorption through skin or ingestion.] Heat the mixture to dissolve the solids and dilute to 5 I. Filter if the solution is not clear. The pH of this solution should lie between 6.9 and 7.1 adjust by the addition of hydrochloric acid or magnesium oxide as necessary. 

Vitamin D. Vitamin D is a steroidlike hormone that can be obtained from dietary sources or synthesized in the skin from cholesterol derivatives in the presence of ultraviolet light. Vitamin D produces several metabolites that are important in bone mineral homeostasis.27,31 In general, vitamin D derivatives such as 1,25 dihydroxyvitamin D3 increase serum calcium and phosphate levels by increasing intestinal calcium and phosphate absorption and by decreasing renal calcium and phosphate excretion.27,46... 

The absorption of vinyl chloride(VC) on surface-treated light-grade and nanoscale calcium carbonate was shown to obey the Langmuir isothermal equation in VC/calcium carbonate/water system. The absorption of VC on calcium carbonate was shown to increase with increase of the partial pressure of VC up to the saturation absorption and the absorption of VC on nanoscale calcium carbonate was greater than that of light-grade calcium carbonate at the same temp, and partial pressure of VC. The presence of calcium carbonate in VC suspension polymerisation system was found to influence the pressure/temp./ conversion(PTC) relationship of the reaction system. Based on the absorption of VC on calcium carbonate and VC distribution in vapour, water and polymer phases, a modified model to represent the PTC relationship of VC suspension polymerisation in the presence of calcium carbonate was proposed. 10 refs. 

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