Photochemistry of dyes and fluorochromes used in biology and medicine: some physicochemical background and current applications

An overview of the basic principles of photochemistry is presented to facilitate discussion of fluorescence, quenching and quantum yields. These topics in turn provide the foundation for an account of fluorescence spectroscopy and its application to microscopy. A brief overview of light microscopy and the application of fluorescence microscopy is given. The influences of molecular features, such as aromatic character and substitution patterns, on color and fluorescence are described. The concept of color fading is considered with particular reference to its effect on microscopic preparations. A survey of representative fluorescent probes is provided, and their sensitivity, application, and limitations are described. The phototoxicity of fluorescent molecules is discussed using biomembranes and DNA as examples of targets of toxicity. Photodynamic therapy, a relatively new clinical application of phototoxicity, is described. Both anticancer and antimicrobial applications are noted, and an assessment is given of the current ideas on the ideal physicochemical properties of the sensitizing agents for such applications.     

Essential Role of the m2R-RGS6-IKACh Pathway in Controlling Intrinsic Heart Rate Variability

Normal heart function requires generation of a regular rhythm by sinoatrial pacemaker cells and the alteration of this spontaneous heart rate by the autonomic input to match physiological demand. However, the molecular mechanisms that ensure consistent periodicity of cardiac contractions and fine tuning of this process by autonomic system are not completely understood.Here we examined the contribution of the m₂R-I_KACh intracellular signaling pathway, which mediates the negative chronotropic effect of parasympathetic stimulation, to the regulation of the cardiac pacemaking rhythm. Using isolated heart preparations and single-cell recordings we show that the m₂R-I_KACh signaling pathway controls the excitability and firing pattern of the sinoatrial cardiomyocytes and determines variability of cardiac rhythm in a manner independent from the autonomic input. Ablation of the major regulator of this pathway, Rgs6, in mice results in irregular cardiac rhythmicity and increases susceptibility to atrial fibrillation. We further identify several human subjects with variants in the RGS6 gene and show that the loss of function in RGS6 correlates with increased heart rate variability. These findings identify the essential role of the m₂R-I_KACh signaling pathway in the regulation of cardiac sinus rhythm and implicate RGS6 in arrhythmia pathogenesis.     

Elastin metabolism during recovery from impaired crosslink formation

Accelerated proteolysis of tropoelastin and elastin occurs in the arteries of chicks rendered nutritionally copper-deficient. The process results in part from decreased elastin crosslinking. Repletion of copper-deficient chicks with copper causes a deposition of elastin that is proteinase resistant. Resistance to proteolysis is conferred within 48 h of dietary copper repletion. Deposition of aorta elastin to near normal values occurs after 3-4 days in copper-repleted chicks. Moreover, elastolysis was enhanced when the content of dehydrolysinonorleucine in elastin was abnormally low. The chemical modification of lysyl residue in elastin by citroconylation, however, did not influence the rate of elastolysis. We have shown previously that tropoelastin messenger RNA activity and synthesis are not influenced by dietary copper deprivation (1986, Biochem. J. 236, 17-23). Rather, as demonstrated herein, the decrease in elastin content in arteries of copper-deficient birds appears to be more the result of enhanced degradation. Restoration of normal crosslinking restores deposition and imparts resistance to elastolysis. Moreover, serum appears to be a good source of elastolytic proteinases when the elastin substrate is partially or abnormally crosslinked.     

Uptake of solutes by multiple root systems from soil

Summary A procedure is put forward for calculating the plant uptake of solutes supplied by diffusion and mass flow to the randomly dispersed roots of a developing root system. The model was tested as follows: (a) for a constant root density, and both transport processes—against a more accurate numerical solution of the same system (b) for an increasing root density, and for supply by diffusion only—by electrical simulation using the analog described in Part I. In both cases, results obtained by the two types of calculation were in close agreement. A less accurate method which includes both supply mechanisms and does not require a computer is presented, and compared with an electrical simulation when there is no mass flow. Agreement is within 20 per cent. The model should be useful for predicting plant nutrient uptake from soil, and may be of special interest to modellers of the whole plant system. re]19720905 Soil Science Laboratory, Department of Agricultural Science ,University of Oxford Present address: Department of Plant Sciences,University of Leeds     

Cortisol stress response and histopathological alteration index in Clarias gariepinus exposed to sublethal concentrations of Qua Iboe crude oil and rig wash

The histological effect on and stress response of post juvenile Clarias gariepinus exposed to Qua Iboe crude oil and rig wash were investigated. Fish weighing 60–90 g and measuring 16–18 cm were exposed for 7–28 days to 8.00 ml^?1 Qua Iboe crude oil and 0.0018 ml^–1 rig wash, both being 0.1 of the 96 hr LC₅₀. Blood samples of C. gariepinus were collected every seven days and evaluated for stress by measuring cortisol concentration. The gills and liver were studied and scored for Gill Alteration Index (GAI) and Hepatic Alteration Index (HAI), respectively. There was an increase in cortisol level up to the 7th and 14th day among the group exposed to Qua Iboe crude oil, with a decrease on the 21st and 28th day. The rig wash group increased in cortisol level up to the 7th day and decreased slightly on the 14th day, after which the trend became irregular. The toxic effects of the Qua Iboe crude oil and rig wash were time dependent, as shown by the histopathological alteration index (HAI) of gill and liver. After 28 days of exposure, the gills had irreparable damage due to high frequency of cellular necrosis and degeneration, whereas the liver had from moderate to severe damage due to the high frequency of cellular degeneration and inflammation. Qua Iboe crude oil and rig wash are both toxic to C. gariepinus, therefore their indiscriminate discharge to the environment must be discouraged.