Temperature cycles induce a bimodal activity pattern in ruin lizards: masking or clock-controlled event? A seasonal problem.

The daily locomotor activity pattern of Ruin lizards in the field is mainly unimodal, except for summer months when soil temperatures exceed 40 degrees C to 42 degrees C around midday. In such a situation, lizards reduce their locomotor activity around midday to avoid overheating, and thus their daily activity pattern becomes bimodal. The bimodal pattern expressed in the field is usually retained in the free-running rhythm under constant temperature and DD for a couple of weeks, after which the bimodal pattern changes into a unimodal pattern. In the present study, the authors examined whether 24-h temperature cycles (TCs) would change lizard activity from a unimodal to a bimodal pattern. Administration of TCs to unimodal lizards free-running in DD is able to entrain locomotor rhythms and to induce a bimodal pattern both in summer and autumn-winter. There are, however, striking seasonal differences in the effectiveness with which TCs achieve bimodality: (a) Numbers of lizards rendered bimodal are significantly higher in summer than in autumn-winter; (b) TCs require less time to achieve bimodality in summer than autumn-winter; (c) bimodality is retained as an aftereffect in the postentrainment free-run in summer, but not in autumn-winter; (d) TCs change activity duration in summer, but not in autumn-winter. All this demonstrates the existence of seasonal changes in responsiveness of the circadian oscillators controlling activity to the external factors inducing bimodality. Oscillators' responsiveness is high in summer, when bimodality is the survival strategy of Ruin lizards to avoid overheating around midday in open fields, and low in autumn-winter, when bimodality has no recognizable adaptive significance.     

The nature of the neutral Na+−Cl−-coupled entry at the apical membrane of rabbit gallbladder epithelium: I. Na+/H+, Cl−/HCO 3 − double exchange and Na+−Cl− symport

Summary Cl^– influx at the luminal border of the epithelium of rabbit gallbladder was measured by 45-sec exposures to³⁶Cl^– and³H-sucrose (as extracellular marker). Its paracellular component was evaluated by the use of 25mm SCN^– which immediately and completely inhibits Cl^– entry into the cell. Cellular influx was equal to 16.7eq cm^–2 hr^–1 and decreased to 8.5eq cm^–2 hr^–1 upon removal of HCO ₃ ^– from the bathing media and by bubbling 100% O₂ for 45 min. When HCO ₃ ^– was present, cellular influx was again about halved by the action of 10^–4 m acetazolamide, 10^–5 to 10^–4 m furosemide, 10^–5 to 10^–4 m 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS), 10^–3 m amiloride. The effects of furosemide and SITS were tested at different concentrations of the inhibitor and with different exposure times: they were maximal at the concentrations reported above and nonadditive. In turn, the effects of amiloride and SITS were not additive. Acetazolamide reached its maximal action after an exposure of about 2 min. When exogenous HCO ₃ ^– was absent, the residual cellular influx was insensitive to acetazolamide, furosemide and SITS. When exogenous HCO ₃ ^– was present in the salines, Na⁺ removal from the mucosal side caused a slow decline of cellular Cl^– influx; conversely, it immediately abolished cellular Cl^– influx in the absence of HCO ₃ ^– . In conclusion, about 50% of cellular influx is sensitive to HCO ₃ ^– , inhibitable by SCN^–, acetazolamide, furosemide, SITS and amiloride and furthermore slowly dependent on Na⁺. The residual cellular influx is insensitive to bicarbonate, inhibitable by SCN^–, resistant to acetazolamide, furosemide, SITS and amiloride, and immediately dependent on Na⁺. Thus, about 50% of apical membrane NaCl influx appears to result from a Na⁺/H⁺ and Cl^–/HCO ₃ ^– exchange, whereas the residual influx seems to be due to Na⁺–Cl^– contranport on a single carrier. Whether both components are simultaneously present or the latter represents a cellular homeostatic counterreaction to the inhibition of the former is not clear.     

Sonic Hedgehog-induced proliferation requires specific Gα inhibitory proteins

Proliferation of cerebellar granular neuronal precursors (CGNPs) is mediated by Sonic Hedgehog (Shh), which activates the Patched and Smoothened (Smo) receptor complex. Although its protein sequence suggests that Smo is a G protein coupled receptor (GPCR), the evidence that this receptor utilizes heterotrimeric G proteins as downstream effectors is controversial. In Drosophila, Gα(i) is required for Hedgehog (Hh) activity, but the involvement of heterotrimeric G proteins in vertebrate Shh signaling has not yet been established. Here, we show that Shh-induced proliferation of rat CGNPs is enhanced strongly by the expression of the active forms of Gα(i/o) proteins (Gα(i1), Gα(i2), Gα(i3), and Gα(o)) but not by members of another class (Gα(12)) of heterotrimeric G proteins. Additionally, the mRNAs of these different Gα(i) members display specific expression patterns in the developing cerebellum; only Gα(i2) and Gα(i3) are substantially expressed in the outer external granular layer, where CGNPs proliferate. Consistent with this, Shh-induced proliferation of CGNPs is reduced significantly by knockdowns of Gα(i2) and Gα(i3) but not by silencing of other members of the Gα(i/o) class. Finally, our results demonstrate that Gα(i2) and Gα(i3) locate to the primary cilium when expressed in CGNP cultures. In summary, we conclude that the proliferative effects of Shh on CGNPs are mediated by the combined activity of Gα(i2) and Gα(i3) proteins.     

Resolvin d1 and resolvin d2 govern local inflammatory tone in obese fat

The unprecedented increase in the prevalence of obesity and obesity-related disorders is causally linked to a chronic state of low-grade inflammation in adipose tissue. Timely resolution of inflammation and return of this tissue to homeostasis are key to reducing obesity-induced metabolic dysfunctions. In this study, with inflamed adipose, we investigated the biosynthesis, conversion, and actions of Resolvins D1 (RvD1, 7S,8R,17S-trihydroxy-4Z,9E,11E,13Z,15E,19Z-docosahexaenoic acid) and D2 (RvD2, 7S,16R,17S-trihydroxy-4Z,8E,10Z,12E,14E,19Z-docosahexaenoic acid), potent anti-inflammatory and proresolving lipid mediators (LMs), and their ability to regulate monocyte interactions with adipocytes. Lipid mediator-metabololipidomics identified RvD1 and RvD2 from endogenous sources in human and mouse adipose tissues. We also identified proresolving receptors (i.e., ALX/FPR2, ChemR23, and GPR32) in these tissues. Compared with lean tissue, obese adipose showed a deficit of these endogenous anti-inflammatory signals. With inflamed obese adipose tissue, RvD1 and RvD2 each rescued impaired expression and secretion of adiponectin in a time- and concentration-dependent manner as well as decreasing proinflammatory adipokine production including leptin, TNF-α, IL-6, and IL-1β. RvD1 and RvD2 each reduced MCP-1 and leukotriene B(4)-stimulated monocyte adhesion to adipocytes and their transadipose migration. Adipose tissue rapidly converted both resolvins (Rvs) to novel oxo-Rvs. RvD2 was enzymatically converted to 7-oxo-RvD2 as its major metabolic route that retained adipose-directed RvD2 actions. These results indicate, in adipose, D-series Rvs (RvD1 and RvD2) are potent proresolving mediators that counteract both local adipokine production and monocyte accumulation in obesity-induced adipose inflammation.     

Ontogenesis of the vitamin D receptor in rat heart

1,25-Dihydroxyvitamin D(3) through its receptor (vitamin D receptor; VDR) has important physiological effects such as calcium transport and cell growth and differentiation. Although the VDR is present in a variety of cell lines as well as in numerous tissues, including rat and human heart, no data are available about the presence of VDR in heart at different steps of rat life. In this study we evaluated the VDR expression using RT-PCR and immunohistochemical techniques in fetal (17, 18 and 20 gestational days), neonatal (4 and 8 days) and adult rat heart. Immunohistochemical techniques showed the VDR protein localisation in the nuclei of cardiac muscle fibres. Also, we demonstrated that VDR mRNA expression is changing over these different periods of development, showing significant differences in 20 days versus 18 days of fetal age. These changes in VDR expression may be related to other parameters associated with the development of the cardiac muscle and/or intracellular cardiac cell calcium homeostasis.     

Methenyltetrahydrofolate synthetase regulates folate turnover and accumulation

Cellular folate deficiency impairs one-carbon metabolism, resulting in decreased fidelity of DNA synthesis and inhibition of numerous S-adenosylmethionine-dependent methylation reactions including protein and DNA methylation. Cellular folate concentrations are influenced by folate availability, cellular folate transport efficiency, folate polyglutamylation, and folate turnover specifically through degradation. Folate cofactors are highly susceptible to oxidative degradation in vitro with the exception of 5-formyltetrahydrofolate, which may be a storage form of folate. In this study, we determined the effects of depleting cytoplasmic 5-formyltetrahydrofolate on cellular folate concentrations and folate turnover rates in cell cultures by expressing the human methenyltetrahydrofolate synthetase cDNA in human MCF-7 cells and SH-SY5Y neuroblastoma. Cells with increased methenyltetrahydrofolate synthetase activity exhibited: 1) increased rates of folate turnover, 2) elevated generation of p-aminobenzoylglutamate in culture medium, 3) depressed cellular folate concentrations independent of medium folic acid concentrations, and 4) increased average polyglutamate chain lengths of folate cofactors. These data indicate that folate catabolism and folate polyglutamylation are competitive reactions that influence cellular folate concentrations, and that increased methenyltetrahydrofolate synthetase activity accelerates folate turnover rates, depletes cellular folate concentrations, and may account in part for tissue-specific differences in folate accumulation.     

3D Computational Mechanics Elucidate the Evolutionary Implications of Orbit Position and Size Diversity of Early Amphibians

For the first time in vertebrate palaeontology, the potential of joining Finite Element Analysis (FEA) and Parametrical Analysis (PA) is used to shed new light on two different cranial parameters from the orbits to evaluate their biomechanical role and evolutionary patterns. The early tetrapod group of Stereospondyls, one of the largest groups of Temnospondyls is used as a case study because its orbits position and size vary hugely within the members of this group. An adult skull of Edingerella madagascariensis was analysed using two different cases of boundary and loading conditions in order to quantify stress and deformation response under a bilateral bite and during skull raising. Firstly, the variation of the original geometry of its orbits was introduced in the models producing new FEA results, allowing the exploration of the ecomorphology, feeding strategy and evolutionary patterns of these top predators. Secondly, the quantitative results were analysed in order to check if the orbit size and position were correlated with different stress patterns. These results revealed that in most of the cases the stress distribution is not affected by changes in the size and position of the orbit. This finding supports the high mechanical plasticity of this group during the Triassic period. The absence of mechanical constraints regarding the orbit probably promoted the ecomorphological diversity acknowledged for this group, as well as its ecological niche differentiation in the terrestrial Triassic ecosystems in clades as lydekkerinids, trematosaurs, capitosaurs or metoposaurs.     

Dihydrolipoamide dehydrogenase: functional similarities and divergent evolution of the pyridine nucleotide-disulfide oxidoreductases

Dihydrolipoamide dehydrogenase (E3) is the common component of the three alpha-ketoacid dehydrogenase complexes oxidizing pyruvate, alpha-ketoglutarate, and the branched-chain alpha-ketoacids. E3 also participates in the glycine cleavage system. E3 belongs to the enzyme family called pyridine nucleotide-disulfide oxidoreductases, catalyzing the electron transfer between pyridine nucleotides and disulfide compounds. This review summarizes the information available for E3 from a variety of species, from a halophilic archaebacterium which has E3 but no alpha-ketoacid dehydrogenase complexes, to mammalian species. Evidence is reviewed for the existence of two E3 isozymes (one for pyruvate dehydrogenase complex and alpha-ketoglutarate dehydrogenase complex and the other for branched-chain alpha-ketoacid dehydrogenase complex) in Pseudomonas species and for possible mammalian isozymes of E3, one associated with the three alpha-ketoacid dehydrogenase complexes and one for the glycine cleavage system. The comparison of the complete amino acid sequences of E3 from Escherichia coli, yeast, pig, and human shows considerable homologies of certain amino acid residues or short stretches of sequences, especially in the specific catalytic and structural domains. Similar homology is found with the limited available amino acid sequence information on E3 from several other species. Sequence comparison is also presented for other member flavoproteins [e.g., glutathione reductase and mercury(II) reductase] of the pyridine nucleotide-disulfide oxidoreductase family. Based on the known tertiary structure of human glutathione reductase it may be possible to predict the domain structures of E3. Additionally, the sequence information may help to better understand a divergent evolutionary relationship among these flavoproteins in different species.     

Mass transfer characteristics of hydrophobic tubing membrane sensors

Summary The total resistance to transfer through a hydrophobic membrane used in the tubing method is due to an external liquid film and to the membrane itself. The global mass transfer coefficient is higher for alcohols than for other tested volatiles. PTFE microporous membranes are recommended.