Ba2+ unmasks K+ modulation of the Na+-K+ pump in the frog retinal pigment epithelium

This paper presents electrophysiological evidence that small changes in [K+]o modulate the activity of the Na+-K+ pump on the apical membrane of the frog retinal pigment epithelium (RPE). This membrane also has a large relative K+ conductance so that lowering [K+]o hyperpolarizes it and therefore increases the transepithelial potential (TEP). Ba2+, a K+ channel blocker, eliminated these normal K+-evoked responses; in their place, lowering [K+]o evoked an apical depolarization and TEP decrease that were blocked by apical ouabain or strophanthidin. These data indicate that Ba2+ blocked the major K+ conductance(s) of the RPE apical membrane and unmasked a slowing of the normally hyperpolarizing electrogenic Na+-K+ pump caused by lowering [K+]o. Evidence is also presented that [K+]o modulates the pump in the isolated RPE under physiological conditions (i.e., without Ba2+). In the intact retina, light decreases subretinal [K+]o and produces the vitreal-positive c-wave of the electroretinogram (ERG) that originates primarily in the RPE from a hyperpolarization of the apical membrane and TEP increase. When Ba2+ was present in the retinal perfusate, the apical membrane depolarized in response to light and the TEP decreased so that the ERG c-wave inverted. The retinal component of the c-wave, slow PIII, was abolished by Ba2+. The effects of Ba2+ were completely reversible. We conclude that Ba2+ unmasks a slowing of the RPE Na+-K+ pump by the light-evoked decrease in [K+]o. Such a response would reduce the amplitude of the normal ERG c-wave.     

适用于获取最优化配方的一种算法

本文应用印楝种仁提取物（F3）与敌敌畏混配为例,以斜纹夜蛾（Spodopteralitura）为目标害虫,介绍一种适用于获取最优化配方的算法,在二次通用回归旋转组合设计的基础上,经参数辨识,获取二次回归方程,经失拟性、回归显著性检验,本方程基本能够反映杀虫剂用量与斜纹夜蛾幼虫死亡机率值之间的关系．在害虫防治实践中,要求在防治费用最小的基础上,目标害虫有最大的死亡率.因此,以防治目标害虫的费用作为优化算法的目标函数,以害虫死亡机率值最大作为约束条件,有如下的一组优化算式为目标函数约束条件式中a1,a2分别为参试杀虫剂1,2最低用量,b1,b2则为相应的最高用量．C1,C2分别为杀虫剂1,2的单价,N1,N2为杀虫剂l,2的用量．Y为目标害虫死亡机率值回归方程．本文所依据的试验设计中,以对数函数关系变换编码值与使用浓度之间的关系,所以应用拉格朗日求极值原理求取最优化配方．由计算所得的混配比例与其他方法所获结果一致．     

Development of DNA markers for identifying chrysanthemum cultivars generated by ion-beam irradiation

Four chrysanthemum cultivars were generated through (carbon) ion-beam irradiation of the original ‘Jimba’ (Chrysanthemum morifolium Ramat.). The new cultivars had acquired a number of superior cultivation traits, while remaining identical to the commercially available ‘Jimba’ in appearance. In this study, polymerase chain reaction (PCR) assays were used to detect the mutated region of each strain, thereby allowing clear identification at the molecular level. PCR assays were performed with 446 primer sets, including random amplified polymorphic DNA (RAPD) primer sets (10-mer RAPD), arbitrarily primed (AP)-PCR primers based on retrotransposon-like sequences and modified RAPD primers (15-mer RAPD). 15-mer RAPD primers generated a 1.49-fold increased band number at high annealing temperatures compared with the original 10-mer RAPD primers and could thus be effective for detection of polymorphic patterns. Our results provide information on the mutated regions of these ion-beam-irradiated chrysanthemum cultivars. Thus, specific DNA markers could be used to improve identification of new cultivars of chrysanthemum as well as other clonal cultivars of horticultural and agricultural crops.     

Glial cells contribute more to iron and aluminum accumulation but are more resistant to oxidative stress than neuronal cells

Iron (Fe) and aluminum (Al) have been implicated in the pathogenesis of Alzheimer's disease (AD). In this study, we examined neuronal and glial cells to clarify which contributes most to metal accumulation after internalization through the transferrin-independent iron uptake (Tf-IU) systems in primary neuronal and glial predominant (NP and GP) cells from rat cerebral cortex, which affect the accumulation of transition metals in a variety of cultured cells. Al more significantly upregulated the Tf-IU activity in GP cells than in NP cells. GP cells were more resistant to Fe and Al exposure than NP cells. However, a chemiluminescence analysis specific for reactive oxygen species (ROS) showed that ROS levels in Fe- or Al-loaded NP cells were twice as high as in Fe- or Al-loaded GP cells. Northern blot analysis and gel retardation assay showed that the Al and Fe exposure taken up by the cells suppress Tf receptor mRNA expression to a greater extent in GP than NP cells, indicating that Al and Fe more markedly accumulate in glial than in neuronal cells. These results suggest that glial cells rather than neuronal cells contribute to the metal accumulation and are more resistant to oxidative stress caused by metals than neuronal cells. The present study may help to explain the pathogenesis of neurodegeneration in AD disorders caused by metal-generated oxidative stress.     

Nuclear Translocation of Calcium/Calmodulin-dependent Protein Kinase IIδ3 Promoted by Protein Phosphatase-1 Enhances Brain-derived Neurotrophic Factor Expression in Dopaminergic Neurons

We have reported previously that dopamine D₂ receptor stimulation activates calcium/calmodulin-dependent protein kinase II (CaMKII) δ3, a CaMKII nuclear isoform, increasing BDNF gene expression. However, the mechanisms underlying that activity remained unclear. Here we report that CaMKIIδ3 is dephosphorylated at Ser³³² by protein phosphatase 1 (PP1), promoting CaMKIIδ3 nuclear translocation. Neuro-2a cells transfected with CaMKIIδ3 showed cytoplasmic and nuclear staining, but the staining was predominantly nuclear when CaMKIIδ3 was coexpressed with PP1. Indeed, PP1 and CaMKIIδ3 coexpression significantly increased nuclear CaMKII activity and enhanced BDNF expression. In support of this idea, chronic administration of the dopamine D₂ receptor partial agonist aripiprazole increased PP1 activity and promoted nuclear CaMKIIδ3 translocation and BDNF expression in the rat brain substantia nigra. Moreover, aripiprazole treatment enhanced neurite extension and inhibited cell death in cultured dopaminergic neurons, effects blocked by PP1γ knockdown. Taken together, nuclear translocation of CaMKIIδ3 following dephosphorylation at Ser³³² by PP1 likely accounts for BDNF expression and subsequent neurite extension and survival of dopaminergic neurons.     

Molecular pathogenesis of a novel mutation, G108D, in short-chain acyl-CoA dehydrogenase identified in subjects with short-chain acyl-CoA dehydrogenase deficiency

Short-chain acyl-CoA dehydrogenase (SCAD) is a mitochondrial enzyme involved in the β-oxidation of fatty acids. Genetic defect of SCAD was documented to cause clinical symptoms such as progressive psychomotor retardation, muscle hypotonia, and myopathy in early reports. However, clinical significance of SCAD deficiency (SCADD) has been getting ambiguous, for some variants in the ACADS gene, which encodes the SCAD protein, has turned out to be widely prevailed among general populations. Accordingly, the pathophysiology of SCADD has not been clarified thus far. The present report focuses on two suspected cases of SCADD detected through the screening of newborns by tandem mass spectrometry. In both subjects, compound heterozygous mutations in ACADS were detected. The mutated genes were expressed in a transient gene expression system, and the enzymatic activities of the obtained mutant SCAD proteins were measured. The activities of the mutant SCAD proteins were significantly lower than that of the wild-type enzyme, confirming the mechanism underlying the diagnosis of SCADD in both subjects. Moreover, the mutant SCAD proteins gave rise to mitochondrial fragmentation and autophagy, both of which were proportional to the decrease in SCAD activities. The association of autophagy with programed cell death suggests that the mutant SCAD proteins are toxic to mitochondria and to the cells in which they are expressed. The expression of recombinant ACADS-encoded mutant proteins offers a technique to evaluate both the nature of the defective SCAD proteins and their toxicity. Moreover, our results provide insight into possible molecular pathophysiology of SCADD.     

A novel, brain-specific mouse drebrin: cDNA cloning, chromosomal mapping, genomic structure, expression, and functional characterization

Drebrin A, a major neuronal actin-binding protein, regulates the dendritic spine shapes of neurons. Here, we have cloned and characterized a novel mouse cDNA clone encoding a truncated form of drebrin A, named s-drebrin A. Analysis of the genomic organization of the mouse drebrin gene (Dbn1), which mapped to the central portion of chromosome 13, revealed that isoforms including s-drebrin A are generated by alternative splicing from a single drebrin gene. The s-drebrin A mRNA was expressed in the brain, but not in non-neuronal tissues. The s-drebrin A expression was barely detected in the embryonic brain, but was upregulated during postnatal development of the brain. Overexpression of GFP-tagged s-drebrin A in fibroblasts showed it to be associated with actin filaments and with changes in actin cytoskeleton organization. These findings suggest that s-drebrin A has a role in spine morphogenesis, possibly by competing the actin-binding activity with drebrin A.     

Vitamin B12 accelerates re-entrainment of activity rhythms in rats.

The effects of methyl vitamin B12 (5-6 mg/kg, p.o.) on the entrainment of circadian running wheel activity rhythm to a new lighting schedule were measured in rats. After the light-dark (LD) cycle was abruptly reversed, rats given vitamin B12 took less time to entrain their circadian locomotor activity rhythm to the new cycle than did controls. This result indicates that vitamin B12 accelerates the reentrainment of the mammalian circadian activity rhythm following an abrupt change in the environmental LD cycle.