Chlorotetracycline As An Indicator Of The Interaction Of Calcium With Brain Membrane Fractions

The fluorescence of chlorotetracycline (CTC) in the presence of synaptosomes isolated from sheep brain is selectively increased by Ca2+ under conditions in which Mg2+, Na+, K+, Li+ or choline have only a small effect. The monovalent cations release bound Ca2+ from synaptosomes, and this effect is reflected by a decrease in the CTC fluorescence. Under optimal conditions there is a near parallelism between Ca2+ and CTC binding to the synaptosomes membranes, and Li+ is the monovalent cation tested which interferes the most with the binding of both substances. These results obtained in a predominantly sucrose medium become less distinct when media simulating physiological composition are utilized, which limits the usefulness of the method. Brain mitochondria and myelin also bind Ca2+ and CTC. The ratio of the fluorescence signal (or CTC bound) to Ca2+ bound is highest of all for mitochondrial membranes, and the apparent fluorescence quantum yield of CTC is also the highest in these membranes, which suggests that the Ca2+ in these membranes is localized in a more apolar region than is the case for synaptosomes and myelin

Effects of Ultraviolet Radiation on Amphibians: Field Experiments

Numerous reports suggest that populations of amphibians from a wide variety of locations are experiencing population declines and/or range reductions. In some cases, unusually high egg mortality has been reported. Field experiments have been used with increasing frequency to investigate ultraviolet radiation as one of the potential factors contributing to these declines. Results from field experiments illustrate that hatching success of eggs is hampered by ultraviolet radiation in a number of species, while other species appear to be unaffected. Continued mortality in early life-history stages may ultimately contribute to a population decline. Although UV-B radiation may not contribute to the population declines of all species, it may play a role in the population decline of some species, especially those that lay eggs in open shallow water subjected to solar radiation and in those that have a poor ability to repair UV-induced DNA damage.Peer reviewe