Calcium is necessary for light excitation in barnacle photoreceptors

Summary Illumination of barnacle (Balanus amphitrite) photoreceptors is known to increase the membrane permeability to sodium and Ca²⁺ ions resulting in a depolarizing receptor potential. In this report, we show that lanthanum (La³⁺), a known inhibitor of Ca-binding proteins, reversibly eliminates the receptor potential of barnacle photoreceptors when applied to the extracellular space. Similar reversible elimination of the light response was obtained by removing extracellular Ca²⁺ by application of the calcium chelating agent EGTA. Iontophoretic injection of Ca²⁺, but not K⁺ into the cells protected both the transient and the steady-state phases of the receptor potential from elimination by EGTA while only the transient phase was protected in the presence of La³⁺. The EGTA experiments suggest that internal Ca²⁺ is necessary for light excitation of barnacle photoreceptors while the La³⁺ experiments suggest that La³⁺-sensitive inward current is necessary to maintain excitation during prolonged light.Abbreviations EGTA ethylenglyol-bis-(-aminoethylether) N, N, N¹, N¹-tetraacetate - BAPTA bis-(0-aminophenoxy)-ethane-N, N, N¹, N¹-tetraacetic acid - DMSO dimethyl sulfoxide - trp transient receptor potential - nss no steady state - ASW artificial sea water     

Oxidation of methyl derivatives of pteridin-4-one, lumazine and related pteridines by bovine milk xanthine oxidase.

1. Pteridin-4-ones, methylated at nitrogen or carbon, N-methylated lumazines and related oxopteridines were studied as substrates of a highly purified bovine milk xanthine oxidase (xanthine : oxygen oxidoreductase, EC 1.2.3.2). 2. The enzyme can oxidise at high rates both uncharged and anionic substrates. Variation of enzymic activity with pH is mainly due to pH-dependent changes in the active enzymic center. 3. Milk xanthine oxidases at different stages of purification convert pteridin-4-one into the 4,7-dione (compound 13 in this article). 4. Methylation at C-6 in the pyrazine moiety enhances enzymic attack at C-2 in the pyrimidine ring. N-Methylation may increase or reduce rates of oxidation. 5. For oxidation at C-2, the most favorable form of the substrate bears a double bond at C(2) = N(3). Attack at C-7 is enhanced strongly in structures bearing a double bond at C(6) = C(7). 6. In general, pteridines react with xanthine oxidase as non-hydrated molecules. However, oxidation of 8-methyllumazine at C-7 may take place by dehydrogenation of the 7-CHOH group of the covalently hydrated molecule.     

Energization of the sugar transport mechanism in the plasmalemma of isolated mesophyll protoplasts

The mechanism of 3-O-methyl-d-glucose transport through the plasmalemma has been investigated in protoplasts isolated from the mesophyll of Pisum sativum L. var. Dan.Analysis of the fluxes after 50 minutes of uptake showed that the gradual decrease in slope of the net uptake curve with time was not due to any decline in uptake capacity; it represented the approach to flux equilibrium of a small compartment of the protoplast, probably the cytoplasm.The energy of activation for initial flux into this compartment was 20 kilocalories per mole between 17 and 27 C. Very high discrimination was shown with regard to sugar isomers. Light strongly promoted flux (by a factor of 2.5 in the case of methyl glucose). Initial flux showed sharply contrasting inhibitor sensitivity in the light and the dark. Light uptake was sensitive to the proton conductor carbonyl cyanide m-chlorophenylhydrazone (CCCP), but stable for at least the first 10 minutes to the ATPase inhibitors quercetin, rutin, and diethylstilbestrol, as well as to arsenate. Dark uptake, on the other hand, was stable to CCCP but was immediately depressed by quercetin, rutin, diethylstilbestrol, and arsenate.Protoplasts which received a light pretreatment before incubation in the dark took up methyl glucose at the accelerated light rate for the first 7 minutes. Moreover, the light pretreatment sensitized subsequent initial dark uptake to CCCP, and conferred on it the stability to ATPase inhibitors and arsenate characteristic of light uptake. After about 7 minutes the characteristic inhibitor responses of dark uptake were resumed.It is proposed that more than one mode of energy-coupling for sugar transport may operate in these protoplasts.     

Protonation and light synergistically convert plasmalemma sugar carrier system in mesophyll protoplasts to its fully activated form

The course of sugar fluxes into and out of protoplasts isolated from the mesophyll of Pisum sativum L. has been followed over brief time intervals (minutes). Light strongly stimulated net sugar influx at pH 8 as well as at pH 5.5. The proton conductor carbonyl cyanide m-chlorophenylhydrazone (CCCP) inhibited initial influx in the light, both at pH 8.0 and at pH 5.5. CCCP was without effect in the dark at either pH. All these results applied both to sucrose and to the nonmetabolizable glucose analog 3-O-methyl-d-glucose.When protoplasts at pH 5.5 were transferred from light to darkness, "stored" light driving force maintained uptake in the dark at the full light rate for the first 7 minutes. At pH 8, however, even 4 minutes after transfer to dark, uptake was well below the light rate. Initial uptake rates over a range of external concentrations were derived from progress curves obtained in the light and in the dark, both at pH 5.5 and at 7.7. When initial rate was plotted against concentration, simple Michaelis-Menten kinetics were observed only under the condition pH 5.5, light. In the dark at both pH values, and in the light at pH 7.7, complex curves with intermediate plateaus were obtained, strongly resembling curves reported for systems where mixed negative and positive cooperativity is operating.The same "K(m) for protons" was observed in the dark and in the light (10(-7) molar). Switching protoplasts in the dark from pH 8 to 5.5 failed to drive sugar transport by imposed protonmotive force, as judged by lack of sensitivity to CCCP. Switching protoplasts which had taken up sugar in the dark at pH 5.5 to pH 7 induced net efflux of sugar. Flux analysis showed that this effect was entirely due to the prompt fall in influx.It is concluded from the kinetic experiments that protonation alone is not sufficient to convert the sugar transport system to its fully activated high affinity form. A further light-dependent factor which acts synergistically with protonation is required.     

Phenology and polyploidy in annual Brachypodium species (Poaceae) along the aridity gradient in Israel

Local adaptation of plants along environmental gradients provides strong evidence for clinal evolution mediated by natural selection. Plants have developed diverse strategies to mitigate stress, for example, drought escape is a phenological strategy to avoid drought stress, while polyploidy was proposed as a genomic adaptation to stress. Polyploidy as an adaptation to aridity (an environmental parameter integrating temperature and precipitation) was previously documented in annual Brachypodium spp. (Poaceae) in the Western Mediterranean. Here, we examined whether polyploidy or phenology are associated with aridity in annual Brachypodium spp. along the aridity gradient in the Eastern Mediterranean. Using flow cytometry, we determined ploidy levels of plants from natural populations along the Israeli gradient, spanning ∼424 km from mesic Mediterranean to extreme desert climates. In a common garden we recorded time of seedling emergence, flowering and senescence. We tested whether the proportion of allotetraploids in the populations and phenological traits were associated with aridity. Contrary to a previous study in the Western Mediterranean, we found no effect of aridity on the proportion of allotetraploids and diploids within populations. Interestingly, phenology was associated with aridity: time of emergence was later, while flowering and senescence were earlier in desert plants. Our results indicate that in the Eastern Mediterranean, adaptation of Brachypodium to aridity is mediated mainly by phenology, rather than ploidy level. Therefore, we suggest that genome duplication is not the main driver of adaptation to environmental stress; rather, phenological change as a drought escape mechanism may be the major adaptation.     

Calponin 2 Acts As an Effector of Noncanonical Wnt-Mediated Cell Polarization during Neural Crest Cell Migration

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Highlights? Cnn2 is expressed in NCCs and required for their migration in frogs and chicks ? Cnn2 is inactivated by noncanonical Wnt signaling ? Loss of Cnn2 causes a switch from cortical actin to central stress fibers ? Cnn2 polarizes the actin cytoskeleton downstream of PCP     

Genetic Variants in Vitamin D Pathway Genes and Risk of Pancreas Cancer; Results from a Population-Based Case-Control Study in Ontario,Canada

Recent studies of 25-hydroxyvitamin D (25(OH)D) levels and pancreas cancer have suggested a potential role of the vitamin D pathway in the etiology of this fatal disease. Variants in vitamin-D related genes are known to affect 25(OH)D levels and function and it is unknown if these variants may influence pancreatic cancer risk. The association between 87 single nucleotide polymorphisms (SNPs) in 11 genes was evaluated within the Ontario Pancreas Cancer Study, a population-based case-control study. Pancreatic cancer cases with pathology confirmed adenocarcinoma were identified from the Ontario Cancer Registry (n = 628) and controls were identified through random digit dialing (n = 1193). Age and sex adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated by multivariate logistic regression. SNPs in the CYP24A1, CYP2R1, calcium sensing receptor (CASR), vitamin D binding protein (GC), retinoid X receptor-alpha (RXRA) and megalin (LRP2) genes were significantly associated with pancreas cancer risk. For example, pancreas cancer risk was inversely associated with CYP2R1 rs10741657 (AA versus GG, OR = 0.70; 95%CI: 0.51–0.95) and positively with CYP24A1 rs6127119 (TT versus CC. OR = 1.94; 95%CI: 1.28–2.94). None of the associations were statistically significant after adjustment for multiple comparisons. Vitamin D pathway gene variants may be associated with pancreas cancer risk and future studies are needed to understand the possible role of vitamin D in tumorigenesis and may have implications for cancer-prevention strategies.     

Evaluation of helmet and goggle designs by modeling non-penetrating projectile impacts

Despite the progress in developing personal combat-protective gear, eye and brain injuries are still widely common and carry fatal or long-term repercussions. The complex nature of the cranial tissues suggests that simple methods (e.g. crash-dummies) for testing the effectiveness of personal protective gear against non-penetrating impacts are both expensive and ineffective, and there are ethical issues in using animal or cadavers. The present work presents a versatile testing framework for quantitatively evaluating protective performances of head and eye combat-protective gear, against non-penetrating impacts. The biomimetic finite element (FE) head model that was developed provides realistic representation of cranial structure and tissue properties. Simulated crash impact results were validated against a former cadaveric study and by using a crash-phantom developed in our lab. The model was then fitted with various helmet and goggle designs onto which a non-penetrating ballistic impact was applied. Example data show that reduction of the elastic and shear moduli by 30% and 80% respectively of the helmet outer Kevlar-29 layer, lowered intracranial pressures by 20%. Our modeling suggests that the level of stresses that develop in brain tissues, which ultimately cause the brain damage, cannot be predicted solely by the properties of the helmet/goggle materials. We further found that a reduced contact area between goggles and face is a key factor in reducing the mechanical loads transmitted to the optic nerve and eye balls following an impact. Overall, this work demonstrates the simplicity, flexibility and usefulness for development, evaluation, and testing of combat-protective equipment using computational modeling.

• Highlights

• A finite element head model was developed for testing head gear.

• Reduced helmet’s outer layer elastic and shear moduli lowered intracranial stresses.

• Gear material properties could not fully predict impact-related stress in the brain.

• Reduced goggles-face contact lowered transmitted loads to the optic nerve and eyes.