Comparison of Phase Shifts of the Circadian Rhythm of K Uptake in Lemna gibba G3 by Various Amino Acid Analogs

Advances and limits of two model species for ecotoxicological assessment of carbamazepine, two by-products and their mixture at environmental level in freshwater

In order to evaluate the environmental impacts associated with the presence of low-level of pharmaceuticals in waters, chronic ecotoxicity of carbamazepine (CBZ), oxcarbazepine (OxCBZ) and acridine 9-carboxylic acid (9-CAA) and their mixture was investigated using two species from different trophic levels. Innovative approaches were developed by monitoring: (i) phytometabolites in the duckweed Lemna minor L. and, (ii) alterations at the population, cellular and molecular levels on the cnidarian Hydra circumcincta Schulze 1914, to assess the effects of 14-day chronic exposure. On H. circumcincta, the approach was conducted at 19.5 °C, the optimal growth temperature, and at 23 °C, to simulate global warming impact. In L. minor, results showed alterations of the nitrogen balance and the chlorophyll indices for OxCBZ and 9-CAA separately at environmental concentrations and for the mixture of the three studied products. However, phenolic compound index deeply varied depending on pharmaceuticals and time of exposure with no specific trend. In H. circumcincta, effects on morphology, reproduction and lipid peroxidation were observed at low level of CBZ. OxCBZ impacted the total antioxidant capacity of H. circumcincta, whereas exposure to 9-CAA affected all parameters, except the reproduction rate. Finally, 14-day exposure to the mixture of the three products also slowed the reproduction rate and altered the morphology of this cnidarian. Higher damages were detected when experiments were conducted at a temperature 3.5 °C above the optimum for Hydra growth, suggesting the relevance of taking into account possible ecotoxicological consequences of global warming. Our results confirmed the necessity of selecting sensitive organisms at different trophic levels to better assess ecotoxicity of pharmaceuticals and their mixture, especially at environmental levels and facing global changes.

Forty years of PRCs--what have we learned?

What are phase-response curves (PRCs)? How can they be measured? How should they be plotted? These questions and many other fascinating facets of PRCs are addressed in this review, including research topics in which phase-resetting data have provided crucial insights: entrainment, phototransduction, pacemaker mechanism, phase markers of the pacemaker, and gauges of oscillator amplitude. PRCs have enlightened us and will continue to be a valuable tool in clock research.

Phased protein synthesis at several circadian times does not change protein levels in Gonyaulax

The synthesis rates of 13 individual proteins in Gonyaulax polyedra, resolved by two-dimensional gel electrophoresis, were estimated from the amount of 35S methionine incorporated during in vivo pulse labeling at 2-h intervals over one circadian period. The synthesis rates of three proteins, taken as controls, varied 2-3 fold, and no systematic pattern to these variations was apparent. In contrast, the synthesis rates of 10 other proteins varied at least tenfold and in a smooth and systematic pattern. The patterns of protein synthesis were placed into three different groups, the first occurring during the late day/early night phase, the second during the middle of the night phase, and the third during the late night/early day phase. The length of time that individual proteins within each group could incorporate radiolabel was variable, raising the possibility that additional groups might be present. However, both a replicate experiment in continuous light and a light:dark experiment confirmed the presence of at least three different groups of protein synthesis patterns. Unlike the circadian changes in the synthesis rate of the luciferin binding protein, which produces variations in protein levels that correlate with the bioluminescence rhythm, no substantial changes were found in the levels of any other rhythmically synthesized proteins examined.

The cellular mechanism of circadian rhythms--a view on evidence, hypotheses and problems

A stable period length is a characteristic property of circadian oscillations. The question about whether higher frequency oscillators (0.5-8 hr) contribute to or establish the stable circadian periodicity cannot be answered at present. A sequential coupling of quantal subcycles appears possible on the basis of known "ultradian" oscillations. There is, however, no supporting evidence for such a concept. Phase response curves of the circadian clock derived from various perturbing pulses allow qualitative conclusions concerning the perturbed clock process. Deductions from computer simulations also allow conclusions about the phase of this oscillatory process. The distinction between processes (a) essential to the clock mechanism, (b) maintaining and controlling the clock (inputs) and (c) depending on the clock (outputs) on the basis of "oscillatory" and "change of psi or tau after perturbation" seems to be useful but not stringent. Protein synthesis may be an essential or input process. Oscillatory changes of this process may be due to periodic translational control or RNA-supply. Circadian changes in protein concentration and/or activity may depend on periodic synthesis, proteolysis, covalent modifications or aggregations. Specific essential proteins have not been identified conclusively. The large overlap between the group of agents and treatments that phase shift the clock and the group that induces stress proteins suggest that the latter may play a role in the controlling (input) or essential domain. The role of membranes in the clock mechanism is not clear: concepts assuming an essential function are based on circumstantial evidence. The membrane potential as well as Ca2+ may be involved in either input or essential function. Ca(2+)-calmodulin may also be important as concluded from inhibitor experiments. It is tempting to assume that a calmodulin-dependent kinase is part of a periodic protein phosphorylation process, yet it is not clear whether the periodic protein phosphorylation that has been observed is essential or is just another output process.