Repertoire Of Channels Research Articles

Kv1.5 in the Immune System: the Good, the Bad, or the Ugly?

For the last 20 years, knowledge of the physiological role of voltage-dependent potassium channels (Kv) in the immune system has grown exponentially. Leukocytes express a limited repertoire of Kv channels, which contribute to the membrane potential. These proteins are involved in the immune response and are therefore considered good pharmacological targets. Although there is a clear consensus about the physiological relevance of Kv1.3, the expression and the role of Kv1.5 are controversial. However, recent reports indicate that certain heteromeric Kv1.3/Kv1.5 associations may provide insight on Kv1.5. Here, we summarize what is known about this issue and highlight the role of Kv1.5 partnership interactions that could be responsible for this debate. The Kv1.3/Kv1.5 heterotetrameric composition of the channel and their possible differential associations with accessory regulatory proteins warrant further investigation.

Genetically Increased Cell-Intrinsic Excitability Enhances Neuronal Integration into Adult Brain Circuits

New neurons are added to the adult brain throughout life, but only half ultimately integrate into existing circuits. Sensory experience is an important regulator of the selection of new neurons but it remains unknown whether experience provides specific patterns of synaptic input or simply a minimum level of overall membrane depolarization critical for integration. To investigate this issue, we genetically modified intrinsic electrical properties of adult-generated neurons in the mammalian olfactory bulb. First, we observed that suppressing levels of cell-intrinsic neuronal activity via expression of ESKir2.1 potassium channels decreases, whereas enhancing activity via expression of NaChBac sodium channels increases survival of new neurons. Neither of these modulations affects synaptic formation. Furthermore, even when neurons are induced to fire dramatically altered patterns of action potentials, increased levels of cell-intrinsic activity completely blocks cell death triggered by NMDA receptor deletion. These findings demonstrate that overall levels of cell-intrinsic activity govern survival of new neurons and precise firing patterns are not essential for neuronal integration into existing brain circuits.

A phenotypically restricted set of primary afferent nerve fibers innervate the bone versus skin: Therapeutic opportunity for treating skeletal pain

Although musculoskeletal pain is one of the most common causes of chronic pain and physical disability in both developing and developed countries, relatively little is known about the nerve fibers and mechanisms that drive skeletal pain. Small diameter sensory nerve fibers, most of which are C-fiber nociceptors, can be separated into two broad populations: the peptide-rich and peptide-poor nerve fibers. Peptide-rich nerve fibers express substance P (SP) and calcitonin gene-related peptide (CGRP). In contrast, the peptide-poor nerve fibers bind to isolectin B4 (IB4) and express the purinergic receptor P2X3 and Mas-related G protein-coupled receptor member d (Mrgprd). In the present report, we used mice in which the Mrgprd+ nerve fibers express genetically encoded axonal tracers to determine the peptide-rich and peptide-poor sensory nerve fibers that innervate the glabrous skin of the hindpaw as compared to the bone marrow, mineralized bone and periosteum of the femur. Whereas the skin is richly innervated by CGRP+, SP+, P2X3+ and Mrgprd+ sensory nerve fibers, the bone marrow, mineralized bone and periosteum receive a significant innervation by SP+ and CGRP+, but not Mrgprd+ and P2X3+ nerve fibers. This lack of redundancy in the populations of C-fibers that innervate the bone may present a unique therapeutic opportunity for targeting skeletal pain as the peptide-rich and peptide-poor sensory nerve fibers generally express a different repertoire of receptors and channels to detect noxious stimuli. Thus, therapies that target the specific types of C-nerve fibers that innervate the bone may be uniquely effective in attenuating skeletal pain as compared to skin pain.

Measuring diversity of exposure in Guangzhou's television market

This study applied Napoli's (1997) media diversity model to the study of television audiences in Guangzhou, one of China's largest television markets. An analytical framework was developed to organize the measures of exposure diversity, i.e., audience concentration, fragmentation, polarization, and channel repertoires, based on a secondary analysis of peoplemeter data. The results showed that the degree of audience concentration decreased while the degree of audience fragmentation and polarization increased in the market over the course of the past decade. Most notably, the rapid development of both overseas and local television channels greatly diminished CCTV's market monopoly. Overall, patterns of audience fragmentation and polarization are more limited than analogous audience behavior reported in the West.

Cell type‐specific subunit composition of G protein‐gated potassium channels in the cerebellum

G protein-gated inwardly rectifying potassium (GIRK/Kir3) channels regulate cellular excitability and neurotransmission. In this study, we used biochemical and morphological techniques to analyze the cellular and subcellular distributions of GIRK channel subunits, as well as their interactions, in the mouse cerebellum. We found that GIRK1, GIRK2, and GIRK3 subunits co-precipitated with one another in the cerebellum and that GIRK subunit ablation was correlated with reduced expression levels of residual subunits. Using quantitative RT-PCR and immunohistochemical approaches, we found that GIRK subunits exhibit overlapping but distinct expression patterns in various cerebellar neuron subtypes. GIRK1 and GIRK2 exhibited the most widespread and robust labeling in the cerebellum, with labeling particularly prominent in granule cells. A high degree of molecular diversity in the cerebellar GIRK channel repertoire is suggested by labeling seen in less abundant neuron populations, including Purkinje neurons (GIRK1/GIRK2/GIRK3), basket cells (GIRK1/GIRK3), Golgi cells (GIRK2/GIRK4), stellate cells (GIRK3), and unipolar brush cells (GIRK2/GIRK3). Double-labeling immunofluorescence and electron microscopies showed that GIRK subunits were mainly found at post-synaptic sites. Altogether, our data support the existence of rich GIRK molecular and cellular diversity, and provide a necessary framework for functional studies aimed at delineating the contribution of GIRK channels to synaptic inhibition in the cerebellum.

The molecular signature and cis-regulatory architecture of a C. elegans gustatory neuron

Taste receptor cells constitute a highly specialized cell type that perceives and conveys specific sensory information to the brain. The detailed molecular composition of these cells and the mechanisms that program their fate are, in general, poorly understood. We have generated serial analysis of gene expression (SAGE) libraries from two distinct populations of single, isolated sensory neuron classes, the gustatory neuron class ASE and the thermosensory neuron class AFD, from the nematode Caenorhabditis elegans. By comparing these two libraries, we have identified >1000 genes that define the ASE gustatory neuron class on a molecular level. This set of genes contains determinants of the differentiated state of the ASE neuron, such as a surprisingly complex repertoire of transcription factors (TFs), ion channels, neurotransmitters, and receptors, as well as seven-transmembrane receptor (7TMR)-type putative gustatory receptor genes. Through the in vivo dissection of the cis-regulatory regions of several ASE-expressed genes, we identified a small cis-regulatory motif, the "ASE motif," that is required for the expression of many ASE-expressed genes. We demonstrate that the ASE motif is a binding site for the C2H2 zinc finger TF CHE-1, which is essential for the correct differentiation of the ASE gustatory neuron. Taken together, our results provide a unique view of the molecular landscape of a single neuron type and reveal an important aspect of the regulatory logic for gustatory neuron specification in C. elegans.

Gene Therapy for Pain

Gene Therapy for Pain

The action potential in mammalian central neurons

The action potential of the squid giant axon is formed by just two voltage-dependent conductances in the cell membrane, yet mammalian central neurons typically express more than a dozen different types of voltage-dependent ion channels. This rich repertoire of channels allows neurons to encode information by generating action potentials with a wide range of shapes, frequencies and patterns. Recent work offers an increasingly detailed understanding of how the expression of particular channel types underlies the remarkably diverse firing behaviour of various types of neurons.

Channel Repertoires: Using Peoplemeter Data in Beijing

Channel repertoires, the subsets of available channels that viewers actually watch, have typically been measured by relying on respondent recall. Using minute-by-minute peoplemeter data from Beijing, this study operationalized channel repertoire as the channels actually watched for 10 or more consecutive minutes during the week. On average, Chinese viewers used 13 channels, about one third of those available. Older network and local channels accounted for most of the time spent viewing. A regression model was established in which total time spent viewing TV and cable subscription explained 65% of the total variance in repertoire size.

Editor's Note: Broadcast Research in the Americas

Broadcasting and the electronic media of the Americas is the primary theme of this special issue of the Journal. U.S. scholars have studied systems all over the globe, yet little is known about our closest neighbors, especially Canada and Mexico. Included in this special issue is research from a variety of different countries of North, Central, and South America. It is intended to encourage research on the broader spectrum of international topics relating to the countries and electronic media systems of the Western Hemisphere. This issue was edited by two guest editors, David R. Spencer, Professor, Faculty of Information and Media Studies, University of Western Ontario, and Joseph D. Straubhaar, Professor, Department of Radio-Television-Film, University of Texas, Austin. These coeditors began last year with a call for papers, which produced numerous submissions. A limited number were selected for publication here to illustrate the breadth of research activities currently being undertaken. In the mid-1980s the first small steps were taken to eliminate the borders between two North America nations, Canada and the United States. Mexico eventually joined the agreement. Although it was relatively easy to figure out the dimensions under which hard goods could be shipped north and south, cultural goods were another matter. This collection of articles examines the role of North and South America media in a day and age of free trade. In many respects, it is a study in power and how one party relates to another when messages cross both borders and languages. In this issue, two articles focus on South America. Avila-Saavedra looks at the telenovela in Ecuador, a soap opera genre also popular in Mexico, Central American, and South American television. Wiley discusses the evolution of Chilean television in a rapidly approaching globalized world. Two articles focus on a history and criticism of Canadian broadcasting. Terzic provides a glimpse of policy history and political economy as it relates to the development of the pay-per-view system in Canada. Darnell and Wilson look at the sexist language of Vancouver radio, Talk Radio for Guys. Two articles on Mexico provide a look at Mexico's systems from a cultural perspective. Lozano discusses Mexico's public policies in relation to cultural diversity, and Wilkinson writes both history and critical analysis related to Mexican television within a North American Free Trade Agreement environment. Eyal and Cohen round out the Americas, researching the U.S. program Friends. Two additional articles continue the international focus of the issue, but reach across the oceans. Yuan and Webster discuss channel repertoires in Beijing, and Van Buren researches hate speech in a critical analysis of anti-Arab Web animations. The subject of international media is certainly not new to the Journal. However, as can be seen in the following JOBEM bibliography, provided by Professor Straubhaar, there has been comparatively little research from the last 50 years on U.S. systems and thus there is much yet to be accomplished. The purpose of this special issue is to provide a broad overview of what has been done, look at the current research, and hopefully provide a catalyst for future research ideas. This special issue begins with the JOBEM bibliography of research in the Americas. Next, the coeditors drafted an introduction summarizing the past research work with an eye toward the future. JOBEM Research on the Americas: A Bibliography Appelman, D. (1978). The mass media of Latin America: Selected information sources. Journal of Broadcasting, 22, 217-240. Browne, D. R. (1996). Comparing electronic media across cultures: Reflections in a myopic eye? Journal of Broadcasting & Electronic Media, 40, 265-280. Demers, F. (2003). Canadian television: The exhaustion of a domestic paradigm? Journal of Broadcasting & Electronic Media, 47, 656-661. …

Two Flagellar Genes, AGG2 and AGG3, Mediate Orientation to Light in Chlamydomonas

Ciliary membranes have a large repertoire of receptors and ion channels that act to transduce information from the environment to the cell. Chlamydomonas offers a tractable system for dissecting the transport and function of ciliary and flagellar membrane proteins. Isolation of ergosterol and sphingolipid-enriched Chlamydomonas flagellar membrane domains identified potential signaling molecules by mass spectroscopy. These include a membrane protein and a matrix flavodoxin protein that are encoded by the AGG2 and AGG3 genes, respectively. Agg2p localizes to the proximal flagellar membrane near the basal bodies. Agg3p is distributed throughout the flagellar matrix, with an increased concentration in the proximal regions where Agg2p is located. Chlamydomonas cells sense light by using a microbial-type rhodopsin , transduce a signal from the cell body to the flagella, and alter the waveform of the flagella to turn a cell toward the light. Protein depletion by RNA interference reveals that both AGG gene products play roles in the orientation of cells to a directional light source. The depleted strains mimic the phenotype of the previously identified agg1 mutant, which swims away from light. We propose that the localization of Agg2p and Agg3p to the proximal region of the flagella may be important for interpreting light signals.

Molecular and Cellular Diversity of Neuronal G-Protein-Gated Potassium Channels

Neuronal G-protein-gated potassium (GIRK) channels mediate the inhibitory effects of many neurotransmitters. Although the overlapping distribution of GIRK subunits suggests that channel composition varies in the CNS, little direct evidence supports the existence of structural or functional diversity in the neuronal GIRK channel repertoire. Here we show that the GIRK channels linked to GABAB receptors differed in two neuron populations. In the substantia nigra, GIRK2 was the principal subunit, and it was found primarily in dendrites of neurons in the substantia nigra pars compacta (SNc). Baclofen evoked prominent barium-sensitive outward current in dopamine neurons of the SNc from wild-type mice, but this current was completely absent in neurons from GIRK2 knock-out mice. In the hippocampus, all three neuronal GIRK subunits were detected. The loss of GIRK1 or GIRK2 was correlated with equivalent, dramatic reductions in baclofen-evoked current in CA1 neurons. Virtually all of the barium-sensitive component of the baclofen-evoked current was eliminated with the ablation of both GIRK2 and GIRK3, indicating that channels containing GIRK3 contribute to the postsynaptic inhibitory effect of GABAB receptor activation. The impact of GIRK subunit ablation on baclofen-evoked current was consistent with observations that GIRK1, GIRK2, and GABAB receptors were enriched in lipid rafts isolated from mouse brain, whereas GIRK3 was found primarily in higher-density membrane fractions. Altogether, our data show that different GIRK channel subtypes can couple to GABAB receptors in vivo. Furthermore, subunit composition appears to specify interactions between GIRK channels and organizational elements involved in channel distribution and efficient receptor coupling.

Characterization of a proton‐activated, outwardly rectifying anion channel

Anion channels are present in every mammalian cell and serve many different functions, including cell volume regulation, ion transport across epithelia, regulation of membrane potential and vesicular acidification. Here we characterize a proton-activated, outwardly rectifying current endogenously expressed in HEK293 cells. Binding of three to four protons activated the anion permeable channels at external pH below 5.5 (50% activation at pH 5.1). The proton-activated current is strongly outwardly rectifying, due to an outwardly rectifying single channel conductance and an additional voltage dependent facilitation at depolarized membrane potentials. The anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) rapidly and potently inhibited the channel (IC50: 2.9 microm). Flufenamic acid blocked this channel only slowly, while mibefradil and amiloride at high concentrations had no effect. As determined from reversal potential measurements under bi-ionic conditions, the relative permeability sequence of this channel was SCN-> I-> NO3-> Br-> Cl-. None of the previously characterized anion channel matches the properties of the proton-activated, outwardly rectifying channel. Specifically, the proton-activated and the volume-regulated anion channels are two distinct and separable populations of ion channels, each having its own set of biophysical and pharmacological properties. We also demonstrate endogenous proton-activated currents in primary cultured hippocampal astrocytes. The proton-activated current in astrocytes is also carried by anions, strongly outwardly rectifying, voltage dependent and inhibited by DIDS. Proton-activated, outwardly rectifying anion channels therefore may be a broadly expressed part of the anionic channel repertoire of mammalian cells.

Specific pattern of ionic channel gene expression associated with pacemaker activity in the mouse heart.

Even though sequencing of the mammalian genome has led to the discovery of a large number of ionic channel genes, identification of the molecular determinants of cellular electrical properties in different regions of the heart has been rarely obtained. We developed a high-throughput approach capable of simultaneously assessing the expression pattern of ionic channel repertoires from different regions of the mouse heart. By using large-scale real-time RT-PCR, we have profiled 71 channels and related genes in the sinoatrial node (SAN), atrioventricular node (AVN), the atria (A) and ventricles (V). Hearts from 30 adult male C57BL/6 mice were microdissected and RNA was isolated from six pools of five mice each. TaqMan data were analysed using the threshold cycle (C(t)) relative quantification method. Cross-contamination of each region was checked with expression of the atrial and ventricular myosin light chains. Two-way hierarchical clustering analysis of the 71 genes successfully classified the six pools from the four distinct regions. In comparison with the A, the SAN and AVN were characterized by higher expression of Nav beta 1, Nav beta 3, Cav1.3, Cav3.1 and Cav alpha 2 delta 2, and lower expression of Kv4.2, Cx40, Cx43 and Kir3.1. In addition, the SAN was characterized by higher expression of HCN1 and HCN4, and lower expression of RYR2, Kir6.2, Cav beta 2 and Cav gamma 4. The AVN was characterized by higher expression of Nav1.1, Nav1.7, Kv1.6, Kvbeta1, MinK and Cav gamma 7. Other gene expression profiles discriminate between the ventricular and the atrial myocardium. The present study provides the first genome-scale regional ionic channel expression profile in the mouse heart.

New phenotypic, functional and electrophysiological characteristics of KG-1 cells

Myeloid dendritic cells (DC) are representatives of a rare and phenotypically diverse population of professional antigen presenting cells possessing high functional heterogeneity and flexibility. Here we studied the phenotypic, functional and electrophysiological characteristics of KG-1 cells, an erythroleukemia model cell line, which shares morphological and physiological similarities with immature and mature myeloid DC. We compared the expression of internalizing receptors and other cell surface molecules, antigen uptake and migration of unstimulated and activated KG-1 cells with the characteristics of immature and mature DC. Unstimulated KG-1 cells were less potent in capturing extracellular materials than immature DC. In contrast to monocyte-derived DC KG-1 cells stimulated by PMA and ionomycin ceased to migrate along the MIP-3β chemokine gradient despite their high expression of CCR7 chemokine receptor and MDR, a transporter implicated in DC migration. Moreover, we determined the ion channel repertoire of KG-1 cells before and after treatment with PMA and ionomycin by using the patch-clamp technique. We found that both unstimulated and activated KG-1 cells expressed time- and voltage-independent, ChTx sensitive intracellular Ca 2+-gated potassium conductance suggesting the presence of K Ca channels in their membranes. Based on our results we propose that KG-1 cells resemble myeloid DC but also possess unique phenotypic, functional and electrophysiological characteristics.

Interactivity in Television: Use and Impact of an Interactive Program Guide

This study is designed to examine the uses and impact of interactive program guides (IPGs), a television technology that enables viewer inter- activity. Data were obtained from a television survey of 365 IPG users in a medium-sized Midwestern community. Results showed that age, premium channel subscribership, perceived IPG utility, and IPG complexity were significant predictors for IPG use. Further, the study found evidence that the IPG has influenced users' viewing behaviors. IPG use was related to watching more television, viewing enriched program types, and having a larger digital cable channel repertoire.

Contributions of Kv1.2, Kv1.5 and Kv2.1 subunits to the native delayed rectifier K + current in rat mesenteric artery smooth muscle cells

A large array of voltage-gated K + channel (Kv) genes has been identified in vascular smooth muscle tissues. This molecular diversity underlies the vast repertoire of native Kv channels that regulate the excitability of vascular smooth muscle tissues. The contributions of different Kv subunit gene products to the native Kv currents are poorly understood in vascular smooth muscle cells (SMCs). In the present study, Kv subunit-specific antibodies were applied intracellularly to selectively block various Kv channel subunits and the whole-cell outward Kv currents were recorded using the patch-clamp technique in rat mesenteric artery SMCs. Anti-Kv1.2 antibody (8 μg/ml) inhibited the Kv currents by 29.2 ± 5.9% (n = 6, P < 0.05), and anti-Kv1.5 antibody (6 μg/ml) by 24.5 ± 2.6% (n = 7, P < 0.05). Anti-Kv2.1 antibody inhibited the Kv currents in a concentration-dependent fashion (4–20 μg/ml). Co-application of antibodies against Kv1.2 and Kv2.1 (8 μg/ml each) induced an additive inhibition of Kv currents by 42.3 ± 3.1% (n = 7, P < 0.05). In contrast, anti-Kv1.3 antibody (6 μg/ml) did not have any effect on the native Kv current (n = 6, P > 0.05). A control antibody (anti-GIRK1) also had no effect on the native Kv currents. This study demonstrates that Kv1.2, Kv1.5, and Kv2.1 subunit genes all contribute to the formation of the native Kv channels in rat mesenteric artery SMCs.

Identification of a trafficking determinant localized to the Kv1 potassium channel pore.

The repertoire of Kv1 potassium channels expressed in presynaptic terminals of mammalian central neurons is shaped by intrinsic trafficking signals that determine surface-expression efficiencies of homomeric and heteromeric Kv1 channel complexes. Here, we show that a determinant controlling surface expression of Kv1 channels is localized to the highly conserved pore region. Point-mutation analysis revealed two residues as critical for channel trafficking, one in the extracellular "turret" domain and one in the region distal to the selectivity filter. Interestingly, these same residues also form the binding sites for polypeptide neurotoxins. Our findings demonstrate a previously uncharacterized function for the channel-pore domain as a regulator of channel trafficking.

Reconceptualizing Channel Repertoire in the Urban Cable Environment

Channel repertoire, traditionally the sum of the number of channels accessed by a television/cable viewer, is extended: (1) via frequency weighting, (2) with a distinction between primary and specialized repertoires, and (3) by comparing repertoires across achievement and ascriptive social categories (e.g., income, race). In a probability computer-aided telephone interviewing (CATI) survey of 319 metropolitan cable subscribers, analyses of the new repertoires show novel discrimination among social categories and differential predictions from media and attitudinal variables.

The television of abundance arrives: cable choices and interest maximization

Utility theory offers some suggestions for how people react as the so-called “television of abundance” reaches the point where audiences can maximize their interests. Contrasting the interest maximization outlook with the media substitution hypothesis, this study explores cable channel repertoire patterns. A random survey of 319 cable subscribers in a major metropolitan area measured exposure to several dozen channel categories. Utilizing factor analysis, pattern repertoires were developed, comparing social category groupings. Overall, the findings support an interest maximization perspective, with individual category pattern repertoires providing insight into the use of abundant cable offerings to serve specialized needs.