Population dynamics of Armigeres subalbatus (Diptera: Culicidae) across a temperate altitudinal gradient.

Understanding the impacts of weather fluctuations, and environmental gradients, on the abundance of vectors is fundamental to grasp the dynamic nature of the entomological risk for disease transmission. The mosquito Armigeres subalbatus (Coquillet) is a common vector of filariasis. Nevertheless, its population dynamics have been relatively poorly studied. Here, we present results from a season long study where we studied spatio-temporal abundance patterns of Ar. subalbatus across the altitudinal gradient of Mt. Konpira in Nagasaki, Japan. Spatially, we found that abundance of adult Ar. subalbatus decreased with altitude and increased in areas where the ground was rich in leaf litter. Similarly, adult activity was observed only when relative humidity was over 65%. Temporally, we found that peaks in abundance followed large rainfall events. Nevertheless, this mosquito was under significant density dependence regulation. Our results suggest that Ar. subalbatus population peaks following large rainfall events could reflect the recruitment of individuals that were dormant as dry eggs. We did not find a clear signal of temperature on abundance changes of this mosquito, but only on its phenology. Since ground cover seemed more critical than temperature to its spatial distribution, we propose that this mosquito might have some degree of autonomy to changes in temperature.

Transduction of voltage and Ca2+ signals by Slo1 BK channels.

Large-conductance Ca2+ -and voltage-gated K+ channels are activated by an increase in intracellular Ca2+ concentration and/or depolarization. The channel activation mechanism is well described by an allosteric model encompassing the gate, voltage sensors, and Ca2+ sensors, and the model is an excellent framework to understand the influences of auxiliary ß and γ subunits and regulatory factors such as Mg2+. Recent advances permit elucidation of structural correlates of the biophysical mechanism.

Serum inflammatory proteins and frontal lobe dysfunction in patients with cardiovascular risk factors.

BACKGROUND: Recent studies have shown that the levels of circulating inflammatory markers are associated with cognitive decline and cerebral small-vessel disease. Frontal lobe dysfunction is believed to be a relatively characteristic neuropsychological symptom in vascular cognitive impairment caused by cerebral small-vessel disease. The purpose of this study was to investigate whether the levels of serum inflammatory markers are associated with frontal lobe dysfunction, particularly executive dysfunction. METHODS: Between January 2003 and September 2007, 388 patients who had one or more atherosclerotic risk factors and subsequently underwent brain MRI and neuropsychological testing including mini-mental state examination (MMSE), frontal assessment battery (FAB), and modified Stroop test were enrolled in this study. We evaluated the effect of serum levels of inflammatory markers and white matter lesions on frontal lobe function. RESULTS: The FAB score was negatively correlated with serum inflammatory marker levels (hsCRP; r = -0.170, IL-6; r = -0.143, IL-18; r = -0.175) and white matter lesions. In the modified Stroop test, interference measure was positively correlated with the levels of hsCRP (r = -0.198), and IL-18 (r = -0.152), and white matter lesions. However, the MMSE score was not correlated with either inflammatory marker levels. The association between hsCRP and FAB score or interference measure remained significant when controlling for other confounding factors and MRI findings. CONCLUSIONS: The circulating level of hsCRP is associated with frontal lobe dysfunction in patients with cardiovascular risk factors independent of white matter lesions in brain MRI.

Biophysical and molecular mechanisms of Shaker potassium channel inactivation.

The potassium channels encoded by the Drosophila Shaker gene activate and inactivate rapidly when the membrane potential becomes more positive. Site-directed mutagenesis and single-channel patch-clamp recording were used to explore the molecular transitions that underlie inactivation in Shaker potassium channels expressed in Xenopus oocytes. A region near the amino terminus with an important role in inactivation has now been identified. The results suggest a model where this region forms a cytoplasmic domain that interacts with the open channel to cause inactivation.

Restoration of inactivation in mutants of Shaker potassium channels by a peptide derived from ShB.

Site-directed mutagenesis experiments have suggested a model for the inactivation mechanism of Shaker potassium channels from Drosophila melanogaster. In this model, the first 20 amino acids form a cytoplasmic domain that interacts with the open channel to cause inactivation. The model was tested by the internal application of a synthetic peptide, with the sequence of the first 20 residues of the ShB alternatively spliced variant, to noninactivating mutant channels expressed in Xenopus oocytes. The peptide restored inactivation in a concentration-dependent manner. Like normal inactivation, peptide-induced inactivation was not noticeably voltage-dependent. Trypsin-treated peptide and peptides with sequences derived from the first 20 residues of noninactivating mutants did not restore inactivation. These results support the proposal that inactivation occurs by a cytoplasmic domain that occludes the ion-conducting pore of the channel.

Effect of forskolin on voltage-gated K+ channels is independent of adenylate cyclase activation.

Forskolin is commonly used to stimulate adenylate cyclase in the study of modulation of ion channels and other proteins by adenosine 3',5'-monophosphate (cAMP)-dependent second messenger systems. In addition to its action on adenylate cyclase, forskolin directly alters the gating of a single class of voltage-dependent potassium channels from a clonal pheochromocytoma (PC12) cell line. This alteration occurred in isolated cell-free patches independent of soluble cytoplasmic enzymes. The effect of forskolin was distinct from those of other agents that raise intracellular cAMP levels. The 1,9-dideoxy derivative of forskolin, which is unable to activate the cyclase, was also effective in altering the potassium channel activity. This direct action of forskolin can lead to misinterpretation of results in experiments in which forskolin is assumed to selectively activate adenylate cyclase.

A beta2 adrenergic receptor signaling complex assembled with the Ca2+ channel Cav1.2.

The existence of a large number of receptors coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) raises the question of how a particular receptor selectively regulates specific targets. We provide insight into this question by identifying a prototypical macromolecular signaling complex. The beta(2) adrenergic receptor was found to be directly associated with one of its ultimate effectors, the class C L-type calcium channel Ca(v)1.2. This complex also contained a G protein, an adenylyl cyclase, cyclic adenosine monophosphate-dependent protein kinase, and the counterbalancing phosphatase PP2A. Our electrophysiological recordings from hippocampal neurons demonstrate highly localized signal transduction from the receptor to the channel. The assembly of this signaling complex provides a mechanism that ensures specific and rapid signaling by a G protein-coupled receptor.

Domain boundary formation in helical multishell gold nanowires.

Helical multishell gold nanowires are studied theoretically for the formation mechanism of the helical domain boundary. Nanowires with a wire length of more than 10 nm are relaxed by quantum mechanical molecular dynamics simulation with a tight-binding form Hamiltonian. In the results, non-helical nanowires are transformed into helical ones with the formation of atom pair defects at the domain boundary, where the defective atom pair is moved from an inner shell. Analysis of local electronic structure shows a competitive feature of the energy gain of reconstruction on the wire surface and the energy loss of the defect formation. A simple energy scaling theory gives a general explanation of domain boundary formation.

Development of the simulation package 'ELSES' for extra-large-scale electronic structure calculation.

An early-stage version of the simulation package 'ELSES' (extra-large-scale electronic structure calculation) is developed for simulating the electronic structure and dynamics of large systems, particularly nanometer-scale and ten-nanometer-scale systems (see www.elses.jp). Input and output files are written in the extensible markup language (XML) style for general users. Related pre-/post-simulation tools are also available. A practical workflow and an example are described. A test calculation for the GaAs bulk system is shown, to demonstrate that the present code can handle systems with more than one atom species. Several future aspects are also discussed.

Two types of inactivation in Shaker K+ channels: effects of alterations in the carboxy-terminal region.

Shaker potassium channels inactivate and recover from inactivation with multiple exponential components, suggesting the presence of multiple inactivation processes. We describe two different types of inactivation in Shaker potassium channels. N-type inactivation can occur as rapidly as a few milliseconds and has been shown to involve an intracellular region at the amino-terminal acting as a blocker of the pore. C-type inactivation is independent of voltage over a range of -25 to +50 mV. It does not require intact N-type inactivation, but is partially coupled to it. The kinetics of C-type inactivation are quite different for channels with different alternatively spliced carboxy-terminal regions. We have localized the differences in C-type inactivation between the ShB and ShA variants to a single amino acid in the sixth membrane-spanning region. N- and C-type inactivation occur by distinct molecular mechanisms.

Heteromultimeric interactions among K+ channel subunits from Shaker and eag families in Xenopus oocytes.

Heteromultimeric interactions of K+ channel subunits across different families have been thought to contribute to the functional diversity of ionic currents, as suggested by previous genetic evidence. We present here direct demonstration in Xenopus oocytes that subunits from distinct eag and Shaker families functionally interact, most likely as heteromultimeric channels. Coexpression with eag accelerates the inactivation and slows the recovery from inactivation of the transient Shaker current. Site-directed mutagenesis indicates that the eag carboxyl terminus is crucial for this interaction, exerting effects preferentially on N-type inactivation. Many members of the eag and Shaker families have now been identified and their human homologs implicated in cardiac and neurological disorders. Studies on channel subunit interactions may prove important in understanding the disease pattern and the complex functions of the brain.

Properties of ShB A-type potassium channels expressed in Shaker mutant Drosophila by germline transformation.

We have used P element-mediated germline transformation to express ShB channels in Shaker mutant Drosophila and have examined their properties by patch-clamp of embryonic myotubes. The transformed ShB cDNA was placed under the transcriptional control of a heat shock promoter (hsp70). Northern blots revealed that transformed DNA is efficiently transcribed in response to heat shock. Cultured myotubes from the transformants produced large A-type potassium currents in response to heat shock. Although qualitatively similar to native Shaker A-currents in wild-type myotubes, transformant A-current inactivates more rapidly and recovers from inactivation more rapidly, similar to ShB channels expressed in Xenopus oocytes. Unlike the channels in oocytes, however, the transformant A-current is insensitive to 50 nM charybdotoxin.

The I-II loop of the Ca2+ channel alpha1 subunit contains an endoplasmic reticulum retention signal antagonized by the beta subunit.

The auxiliary beta subunit is essential for functional expression of high voltage-activated Ca2+ channels. This effect is partly mediated by a facilitation of the intracellular trafficking of alpha1 subunit toward the plasma membrane. Here, we demonstrate that the I-II loop of the alpha1 subunit contains an endoplasmic reticulum (ER) retention signal that severely restricts the plasma membrane incorporation of alpha1 subunit. Coimmunolabeling reveals that the I-II loop restricts expression of a chimera CD8-I-II protein to the ER. The beta subunit reverses the inhibition imposed by the retention signal. Extensive deletion of this retention signal in full-length alpha1 subunit facilitates the cell surface expression of the channel in the absence of beta subunit. Our data suggest that the beta subunit favors Ca2+ channel plasma membrane expression by inhibiting an expression brake contained in beta-binding alpha1 sequences.

Oxygen sensing in the body.

This review is divided into three parts: (a) The primary site of oxygen sensing is the carotid body which instantaneously respond to hypoxia without involving new protein synthesis, and is historically known as the first oxygen sensor and is therefore placed in the first section (Lahiri, Roy, Baby and Hoshi). The carotid body senses oxygen in acute hypoxia, and produces appropriate responses such as increases in breathing, replenishing oxygen from air. How this oxygen is sensed at a relatively high level (arterial PO2 approximately 50 Torr) which would not be perceptible by other cells in the body, is a mystery. This response is seen in afferent nerves which are connected synaptically to type I or glomus cells of the carotid body. The major effect of oxygen sensing is the increase in cytosolic calcium, ultimately by influx from extracellular calcium whose concentration is 2 x 10(4) times greater. There are several contesting hypotheses for this response: one, the mitochondrial hypothesis which states that the electron transport from the substrate to oxygen through the respiratory chain is retarded as the oxygen pressure falls, and the mitochondrial membrane is depolarized leading to the calcium release from the complex of mitochondria-endoplasmic reticulum. This is followed by influx of calcium. Also, the inhibitors of the respiratory chain result in mitochondrial depolarization and calcium release. The other hypothesis (membrane model) states that K(+) channels are suppressed by hypoxia which depolarizes the membrane leading to calcium influx and cytosolic calcium increase. Evidence supports both the hypotheses. Hypoxia also inhibits prolyl hydroxylases which are present in all the cells. This inhibition results in membrane K(+) current suppression which is followed by cell depolarization. The theme of this section covers first what and where the oxygen sensors are; second, what are the effectors; third, what couples oxygen sensors and the effectors. (b) All oxygen consuming cells have a built-in mechanism, the transcription factor HIF-1, the discovery of which has led to the delineation of oxygen-regulated gene expression. This response to chronic hypoxia needs new protein synthesis, and the proteins of these genes mediate the adaptive physiological responses. HIF-1alpha, which is a part of HIF-1, has come to be known as master regulator for oxygen homeostasis, and is precisely regulated by the cellular oxygen concentration. Thus, the HIF-1 encompasses the chronic responses (gene expression in all cells of the body). The molecular biology of oxygen sensing is reviewed in this section (Semenza). (c) Once oxygen is sensed and Ca(2+) is released, the neurotransmittesr will be elaborated from the glomus cells of the carotid body. Currently it is believed that hypoxia facilitates release of one or more excitatory transmitters from glomus cells, which by depolarizing the nearby afferent terminals, leads to increases in the sensory discharge. The transmitters expressed in the carotid body can be classified into two major categories: conventional and unconventional. The conventional neurotransmitters include those stored in synaptic vesicles and mediate their action via activation of specific membrane bound receptors often coupled to G-proteins. Unconventional neurotransmitters are those that are not stored in synaptic vesicles, but spontaneously generated by enzymatic reactions and exert their biological responses either by interacting with cytosolic enzymes or by direct modifications of proteins. The gas molecules such as NO and CO belong to this latter category of neurotransmitters and have unique functions. Co-localization and co-release of neurotransmitters have also been described. Often interactions between excitatory and inhibitory messenger molecules also occur. Carotid body contains all kinds of transmitters, and an interplay between them must occur. But very little has come to be known as yet. Glimpses of these interactions are evident in the discussion in the last section (Prabhakar).

Accuracy control in ultra-large-scale electronic structure calculations.

Numerical aspects are investigated in ultra-large-scale electronic structure calculations. Accuracy control methods in process (molecular-dynamics) calculations are focused upon. Flexible control methods are proposed so as to control variational freedoms, automatically at each time step, within the framework of generalized Wannier state theory. The method is demonstrated in a silicon cleavage simulation with 10(2)-10(5) atoms. The idea is of general importance among process calculations and is also used in Krylov subspace theory, which is another large-scale calculation theory.

Modulation of BK Channels by Small Endogenous Molecules and Pharmaceutical Channel Openers.

Voltage- and Ca(2+)-activated K(+) channels of big conductance (BK channels) are abundantly found in various organs and their relevance for smooth muscle tone and neuronal signaling is well documented. Dysfunction of BK channels is implicated in an array of human diseases involving many organs including the nervous, pulmonary, cardiovascular, renal, and urinary systems. In humans a single gene (KCNMA1) encodes the pore-forming α subunit (Slo1) of BK channels, but the channel properties are variable because of alternative splicing, tissue- and subcellular-specific auxiliary subunits (ß, γ), posttranslational modifications, and a multitude of endogenous signaling molecules directly affecting the channel function. Initiatives to develop drugs capable of activating BK channels (channel openers) therefore need to consider the tissue-specific variability of BK channel structure and the potential interference with endogenously produced regulatory factors. The atomic structural basis of BK channel function is only beginning to be revealed. However, building on detailed knowledge of BK channel function, including its single-channel characteristics, voltage- and Ca(2+) dependence of channel gating, and modulation by diffusible messengers, a multi-tier allosteric model of BK channel gating (Horrigan and Aldrich (HA) model) has become a valuable tool in studying modulation of the channel. Using the conceptual framework of the HA model, we here review the functional impact of endogenous modulatory factors and select small synthetic compounds that regulate BK channel activity. Furthermore, we devise experimental approaches for studying BK channel-drug interactions with the aim to classify BK-modulating substances according to their molecular mode of action.

Cocaine- and amphetamine-regulated transcript peptide modulation of voltage-gated Ca2+ signaling in hippocampal neurons.

Administration of cocaine and amphetamine increases cocaine- and amphetamine-regulated transcript (CART) expression in the rat striatum (Douglass et al., 1995). CART mRNA is highly expressed in different parts of the human and rat brain, including hippocampus (Douglass et al., 1995; Couceyro et al., 1997; Kuhar and Yoho, 1999; Hurd and Fagergren, 2000). The presence of CART peptide 55-102 immunoreactivity in dense core vesicles of axon terminals suggests that the peptide may be released and may act as a neuromodulator (Smith et al., 1997) to induce neurophysiological and behavioral effects. Little is known, however, about CART peptide-responsive cells, receptor(s), or intracellular signaling mechanisms that mediate CART peptide action. Here we show that CART peptide 55-102 inhibits voltage-dependent intracellular Ca(2+) signaling and attenuates cocaine enhancement of depolarization-induced Ca(2+) influx in rat hippocampal neurons. The inhibitory effect of CART peptide 55-102 on Ca(2+) signaling is likely mediated by an inhibition of L-type voltage-gated Ca(2+) channel activity via a G-protein-dependent pathway. These results indicate that voltage-gated Ca(2+) channels in hippocampal neurons are targets for CART peptide 55-102 and suggest that CART peptides may be important in physiology and behavior mediated by the hippocampus, such as certain forms of learning and memory.

Role of sodium ions in p-aminohippurate transport by newt kidney.

1. The effect of external Na+ concentration on p-aminohippurate uptake by isolated kidneys of newt (Triturus pyrrhogaster) was studied kinetically and electrophysiologically. 2. p-Aminohippurate uptake conformed to Michaelis-Menten type kinetics in regard to both p-aminohippurate and Na+ concentrations in the incubation medium. Kinetic studies revealed that reduction of Na+ concentration increased the values of Kt without altering the maximal rate (V) of p-aminohippurate uptake. The values of Kt were a linear function of the reciprocal of Na+ concentration. These results suggest the presence of interaction between p-aminohippurate and Na+ at the carrier level, i.e. Na+-coupled cotransport. 3. p-Aminohippurate had no effect on the electrical potential difference across the peritubular membrane in both 10 and 100 mM Na+ solutions, suggesting that p-aminohippurate is transported across the peritubular membrane in a form of electrically neutral carrier complex. This is consistent with the results of the kinetic studies. 4. p-Aminohippurate uptake was proportional to the electrochemical potential gradient of Na+ (delta mu Na) across the peritubular membrane. This result indicates that the maintenance of sufficient delta mu Na appears to be necessary for the accumulation of p-aminohippurate against its electrochemical potential gradient, supporting Na+ gradient hypothesis.

Na+-dependent elevation of the acidic cell surface pH (microclimate pH) of rat jejunal villus cells induced by cyclic nucleotides and phorbol ester: possible mediators of the regulation of the Na+/H+ antiporter.

The effects of cyclic nucleotides and phorbol ester on the acidic cell surface pH of rat jejunal villi were studied by using single-barrelled pH-sensitive microelectrodes. Addition of dibutyryl cAMP (1 mM) to the mucosal bathing solution caused an elevation of the cell surface pH from 6.19 +/- 0.04 (n = 12 measurements from three animals) to 6.53 +/- 0.03 (12) in the presence of Na+ in the medium. However, dibutyryl cAMP had no significant effect in the absence of Na+ and presence of 1 mM amiloride. Dibutyryl cGMP (1 mM) also had an Na+-dependent inhibitory effect on the cell surface pH. A phorbol ester, phorbol 12-myristate 13-acetate, caused an elevation of the cell surface pH only in the presence of Na+ from 6.14 +/- 0.07 (12) to 6.46 +/- 0.08 (12). Phorbol and phorbol 13-acetate, which do not stimulate protein kinase C, were without significant effects. These results suggest that increased levels of the intracellular cyclic nucleotides and activation of protein kinase C raise the acidic cell surface pH by inhibiting the activity of the brush-border Na+/H+ antiporter in the rat jejunal villus cells.