Calcium-transport in quiescent and 1,25-dihydroxycholecalciferol-stimulated human osteosarcoma cells. Role in 24 hydroxylase enhancement

The present study evaluates in osteosarcoma cells, the effects of a calcium channel inhibitor nicardipine in 24-hydroxylase activity and 45Ca desaturation curve in presence of 1,25-dihydroxycholecalciferol (1,25(OH)2D3). This sterol induced an increase in 24-OHase activity and 45Ca fluxes. Nicardipine reversed the effect of 1,25(OH)2D3 on 45Ca fluxes but reinforced the enhancement of the 24-OHase activity. The fact that the effects of 1,25(OH)2D3 were reduced by cycloheximide support the hypothesis of a de novo protein synthesis. Our study has allowed us to dissociate the effects of 1,25(OH)2D3 on 24-OHase enhancement from those on Ca2+ transport.     

Effects of iron-induced lipid peroxidation and of acidosis on choline uptake by synaptosomes

The effects of iron-induced lipid peroxidation and of lactic acidosis on [³H]choline uptake were investigated on crude synaptosomes prepared from rat cerebral cortices. Fe²⁺-induced lipid peroxidation as evidenced from the production of thiobarbituric acid reactives substances (TBARS) was correlated with a decrease in high-affinity choline uptake (HACU). Trolox C, a free radical scavenger, prevented both Fe²⁺-induced TBARS production and decrease in HACU. Lactic acidosis (pH 6.0 for 30 or 60 min) increased the TBARS production with concomitant decrease in HACU (–48%, –78%, respectively). The acidosis dependent decrease was not reversible following pH 7.4 readjustment after 60 min acidosis. It was not prevented by trolox C, although trolox C inhibited the acidosis-induced production of TBARS. The results suggest that the contribution of acidosis to peroxidative damages is probably of less importance in comparison to other cytotoxic mechanisms.     

Acidosis-induced modifications of high-affinity choline uptake by synaptosomes: Effects of pH readjustment

Acidosis (pH 6.0) led to significant decrease in high—affinity choline uptake by rat brain synaptosomes. The effects persisted following pH readjustment (7.4) of the incubation medium, consisting of decrease in both Km and Vmax of the affinity system. pH readjustment coincided with synaptosomal leakage of lactate dehydrogenase (LDH) and with instability of the synaptosomal suspension as evidenced from turbidity modifications of the preparation. LDH leakage occurred when acidosis was performed with lactic acid, whereas it was not seen following H₃PO₄ acidosis, probably because of the rapid diffusion of the protonated form of lactic acid across membranes. Turbidity modifications of the suspension were prevented by EDTA. The present results indicate that acidosis to pH level comparable to what is observed in brain ischemia is deleterious for cholinergic mechanisms. They also suggest that alkaline pH shifts that occur after blood reperfusion of ischemic brain tissue might be critical for the survival of cells.To whom to address reprint requests.     

Assessment of the total effective xenoestrogen burden in extracts of human placentas

We have standardized a method to assess the total effective xenoestrogen burden (TEXB) in human placentas by the extraction and separation by high-performance liquid chromatography of two fractions containing lipophilic xenoestrogens (alpha) and endogenous hormones (beta), followed by assessing their estrogenicity in MCF-7 breast cancer cell-based E-Screen and Yeast Estrogen Screen (YES) bioassays. The means of TEXB alpha concentrations (in estradiol equivalent (Eeq) units) were 1.32 and 0.77 Eeq pM g^?1 placenta in the E-Screen and YES, respectively; TEXB beta concentrations were 6.97 and 11.56 Eeq pM g^?1 placenta, respectively. The interclass correlation coefficient was low and a fair level of agreement was observed after kappa test correction. According to the E-Screen and YES, TEXB alpha was ≥LOD in 70.0 and 55.0% of the placentas and 92.5 and 82.5% in beta, respectively. Although both bioassays can be recommended for assessing TEXB, there is greater experience with the use of the E-Screen for estrogenic assessment after extensive extraction of complex human matrices.     

Circulating small non-coding RNAs provide new insights into vitamin K nutrition and reproductive physiology in teleost fish

Background

Vitamin K (VK) is a fat-soluble vitamin known for its essential role in blood coagulation, but also on other biological processes (e.g. reproduction, brain and bone development) have been recently suggested. Nevertheless, the molecular mechanisms behind its particular function on reproduction are not yet fully understood.

Expression of Gla‐rich protein (GRP) in newly developed cartilage‐derived cell cultures from sturgeon (Acipenser naccarii)

Sturgeons are representative of an ancient fish group, and present mainly an internal cartilaginous skeleton, with bone found essentially in the ganoid plaques forming the exogenous skeleton. Because of its archaic genetics, sturgeon represents an important model organism to understand the role of bone and cartilage‐related Gla proteins and determine if their molecular mechanisms of action were maintained throughout evolution. Of particular relevance is understanding the regulation, in sturgeon, of those proteins known to be involved in tissue mineralization in mammals, as well as unveiling the function of newly identified calcification‐related genes such as the one encoding the recently discovered Gla‐rich protein (GRP), thus contributing to understand the poor calcification observed in sturgeon endoskeleton. However, regulation of gene expression and promoter functional analysis of sturgeon cartilage and bone‐specific genes has been hampered by lack of suitable in vitro cell systems. We have recently developed the first sturgeon vertebra (VAn2H) and branchial arches (BAAn1F) derived cell cultures, and here we report their inability to mineralize their ECM under mineralizing culture conditions, as detected by von Kossa staining. Although a more extensive characterization of these systems is ongoing, our first data indicate that these cells represent a valuable tool for expression analysis of sturgeon bone and cartilage genes.     

The influence of white seabream (Diplodus sargus) production on macrobenthic colonization patterns

The present work evaluates the influence of fish production on macrobenthic colonization over large areas (approximately 700 m²), where the colonizing populations are not nearby the disturbed area. Sampling was undertaken within newly created aquaculture earthen ponds under two contrasting conditions: white seabream (Diplodus sargus) production and no production (control). Macrobenthic and geochemical samples were collected 7, 23, 54, 93 and 180 days after filling the earthen ponds with seawater pumped from a water reservoir for the first time. The water reservoir was also sampled, and is used as a reference for the colonizing populations. Macrobenthic colonization rate in the ponds was low, probably due to the isolation of the disturbed habitat, to the large size of the defaunated area, and possibly to geochemical constraints. Initial colonization was by insect larvae (mainly chironomids), the bivalves Cerastoderma spp., the polychaetes Pseudopolydora paucibranchiata and Hydrodoides elegans, and nemerteneans. The number of species was similar in control and production ponds, even though under production higher total abundance values were observed. Although well represented in the water reservoir, the amphipod Microdeutopus gryllotalpa was only observed within the new ponds after 6 months. Preliminary results suggest that macrobenthic colonization patterns were influenced by fish production, as assemblages were significantly different among ponds. Higher food availability due to fish production may explain the results obtained, but ecological reasons, such as predation, may also contribute for shaping the macrobenthic communities.     

Adaptation to stimulus contrast and correlations during natural visual stimulation

In this study, we characterize the adaptation of neurons in the cat lateral geniculate nucleus to changes in stimulus contrast and correlations. By comparing responses to high- and low-contrast natural scene movie and white noise stimuli, we show that an increase in contrast or correlations results in receptive fields with faster temporal dynamics and stronger antagonistic surrounds, as well as decreases in gain and selectivity. We also observe contrast- and correlation-induced changes in the reliability and sparseness of neural responses. We find that reliability is determined primarily by processing in the receptive field (the effective contrast of the stimulus), while sparseness is determined by the interactions between several functional properties. These results reveal a number of adaptive phenomena and suggest that adaptation to stimulus contrast and correlations may play an important role in visual coding in a dynamic natural environment.