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Excitable Cells (excitable + cell)
Selected Abstracts,-Conotoxin CVIB differentially inhibits native and recombinant N- and P/Q-type calcium channelsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2007Leonid Motin Abstract ,-Conotoxins are routinely used as selective inhibitors of different classes of voltage-gated calcium channels (VGCCs) in excitable cells. In the present study, we examined the potent N-type VGCC antagonist ,-conotoxin CVID and non-selective N- and P/Q-type antagonist CVIB for their ability to block native VGCCs in rat dorsal root ganglion (DRG) neurons and recombinant VGCCs expressed in Xenopus oocytes. ,-Conotoxins CVID and CVIB inhibited depolarization-activated whole-cell VGCC currents in DRG neurons with pIC50 values of 8.12 ± 0.05 and 7.64 ± 0.08, respectively. Inhibition of Ba2+ currents in DRG neurons by CVID (, 66% of total) appeared to be irreversible for >,30 min washout, whereas Ba2+ currents exhibited rapid recovery from block by CVIB (, 80% within 3 min). The recoverable component of the Ba2+ current inhibited by CVIB was mediated by the N-type VGCC, whereas the irreversibly blocked current (, 22% of total) was attributable to P/Q-type VGCCs. ,-Conotoxin CVIB reversibly inhibited Ba2+ currents mediated by N- (CaV2.2) and P/Q- (CaV2.1), but not R- (CaV2.3) type VGCCs expressed in Xenopus oocytes. The ,2,1 auxiliary subunit co-expressed with CaV2.2 and CaV2.1 reduced the sensitivity of VGCCs to CVIB but had no effect on reversibility of block. Determination of the NMR structure of CVIB identified structural differences to CVID that may underlie differences in selectivity of these closely related conotoxins. ,-Conotoxins CVIB and CVID may be useful as antagonists of N- and P/Q-type VGCCs, particularly in sensory neurons involved in processing primary nociceptive information. [source] Calcium and polyamine regulated calcium-sensing receptors in cardiac tissuesFEBS JOURNAL, Issue 12 2003Rui Wang Activation of a calcium-sensing receptor (Ca-SR) leads to increased intracellular calcium concentration and altered cellular activities. The expression of Ca-SR has been identified in both nonexcitable and excitable cells, including neurons and smooth muscle cells. Whether Ca-SR was expressed and functioning in cardiac myocytes remained unclear. In the present study, the transcripts of Ca-SR were identified in rat heart tissues using RT-PCR that was further confirmed by sequence analysis. Ca-SR proteins were detected in rat ventricular and atrial tissues as well as in isolated cardiac myocytes. Anti-(Ca-SR) Ig did not detect any specific bands after preadsorption with standard Ca-SR antigens. An immunohistochemistry study revealed the presence of Ca-SR in rat cardiac as well as other tissues. An increase in extracellular calcium or gadolinium induced a concentration-dependent sustained increase in [Ca2+]i in isolated ventricular myocytes from adult rats. Spermine (1,10 mm) also increased [Ca2+]i. Pre-treatment of cardiac myocytes with thapsigargin or U73122 abolished the extracellular calcium, gadolinium or spermine-induced increase in [Ca2+]i. The blockade of Na+/Ca2+ exchanger or voltage-dependent calcium channels did not alter the extracellular calcium-induced increase in [Ca2+]i. Finally, extracellular calcium, gadolinium and spermine all increased intracellular inositol 1,4,5-triphosphate (IP3) levels. Our results demonstrated that Ca-SR was expressed in cardiac tissue and cardiomyocytes and its function was regulated by extracellular calcium and spermine. [source] Novel stem/progenitor cells with neuronal differentiation potential reside in the leptomeningeal nicheJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 9b 2009Francesco Bifari Abstract Stem cells capable of generating neural differentiated cells are recognized by the expression of nestin and reside in specific regions of the brain, namely, hippocampus, subventricular zone and olfactory bulb. For other brain structures, such as leptomeninges, which contribute to the correct cortex development and functions, there is no evidence so far that they may contain stem/precursor cells. In this work, we show for the first time that nestin-positive cells are present in rat leptomeninges during development up to adulthood. The newly identified nestin-positive cells can be extracted and expanded in vitro both as neurospheres, displaying high similarity with subventricular zone,derived neural stem cells, and as homogeneous cell population with stem cell features. In vitro expanded stem cell population can differentiate with high efficiency into excitable cells with neuronal phenotype and morphology. Once injected into the adult brain, these cells survive and differentiate into neurons, thus showing that their neuronal differentiation potential is operational also in vivo. In conclusion, our data provide evidence that a specific population of immature cells endowed of neuronal differentiation potential is resident in the leptomeninges throughout the life. As leptomeninges cover the entire central nervous system, these findings could have relevant implications for studies on cortical development and for regenerative medicine applied to neurological disorders. [source] Functions of erg K+ channels in excitable cellsJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 1 2004Jürgen R. Schwarz Abstract Ether-à-go-go -related gene (erg) channels are voltage-dependent K+ channels mediating inward-rectifying K+ currents because of their peculiar gating kinetics. These characteristics are essential for repolarization of the cardiac action potential. Inherited and acquired malfunctioning of erg channels may lead to the long QT-syndrome. However, erg currents have also been recorded in many other excitable cells, like smooth muscle fibres of the gastrointestinal tract, neuroblastoma cells or neuroendocrine cells. In these cells erg currents contribute to the maintenance of the resting potential. Changes in the resting potential are related to cell-specific functions like increase in hormone secretion, frequency adaptation or increase in contractility. [source] KATP channel blockade protects midbrain dopamine neurons by repressing a glia-to-neuron signaling cascade that ultimately disrupts mitochondrial calcium homeostasisJOURNAL OF NEUROCHEMISTRY, Issue 2 2010Damien Toulorge J. Neurochem. (2010) 114, 583,564. Abstract While KATP channels serve primarily as metabolic gatekeepers in excitable cells, they might also participate in other important cellular functions. Here, we demonstrate that KATP channel blockade with the sulfonylurea derivative glibenclamide provided robust protection to dopamine neurons undergoing spontaneous and selective degeneration in midbrain cultures. Unexpectedly, glibenclamide operated not by a direct effect on dopamine neurons but instead by halting the proliferation of a population of immature glial cells lacking astrocytic and microglial markers. The antimitotic effect of glibenclamide appeared essential to unmask a prosurvival phosphoinositide 3-kinase (PI3K)/Akt-dependent signaling pathway that controlled shuttling of calcium from endoplasmic reticulum to mitochondria in dopamine neurons. Preventing integrin-ligand interactions with a decoy ligand, the Arg-Gly-Asp-Ser sequence peptide, reproduced survival promotion by glibenclamide via a mechanism that also required PI3K/Akt-dependent regulation of mitochondrial calcium. Noticeably, Arg-Gly-Asp-Ser did not cause a reduction in glial cell numbers indicating that it prevented the death process downstream of the level at which glibenclamide intervenes. Based on these results, we propose that KATP channel blockade protected dopamine neurons by inhibiting a glia-to-neuron signaling pathway that propagates through integrin/ligand interactions and ultimately disrupts PI3K/Akt-dependent signaling and mitochondrial calcium homeostasis. [source] Characterisation of the effects of potassium channel modulating agents on mouse intestinal smooth muscleJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 3 2002Chi-Kong Yeung The actions of agents which modulate ATP-sensitive potassium (KATP) channels in excitable cells were investigated in an in-vitro preparation of mouse ileum from which the mucosa was removed. A range of potassium channel openers of diverse structure, cromakalim (0.1,100 ,M), pinacidil (0.1,200 ,M) and its analogue P1060 (0.1,200 ,M), SDZ PCO400 ((-)-(3S,4R)-3,4-dihydro-3-hydroxy-2,2-dimethyl-4-(3-oxo-cyclopent-1-enyloxy)-2H -1-benzopyran-6-carbonitrile) (0.3,60 ,M), caused concentration-related reduction in twitch height of electrical field stimulated ileum. P1060 and SDZ PCO400 were the most potent agents; diazoxide (0.1,100 ,M) was without effect. The order of inhibitory potency, based on EC50 values (concentration of a relaxant producing 50% of the maximum inhibition of twitch) was: P1060 = SDZ PCO400 > cromakalim > pinacidil. The relaxant effect of the potassium channel openers was antagonised by the sulfonylureas glibenclamide (0.1-1.0 ,M) and glipizide (3,30 ,M) but the nature of the antagonism differed. Antagonism of P1060 and SDZ PCO400 by glibenclamide appeared to be competitive whereas the antagonism of relaxation induced by cromakalim and pinacidil was apparently not competitive. Both phentolamine (1,10 ,M) and tolbutamide (100,300 ,M) showed competitive antagonism of the actions of pinacidil while yohimbine (1,20 ,M) did not antagonise relaxation and appeared to have actions at sites other than the KATP channel in this preparation. The relative effectiveness of the antagonists on pinacidil-induced relaxation was found to be: glibenclamide >phentolamine >tolbutamide >yohimbine, which is in agreement with studies in other tissues. The results show that many structurally diverse potassium channel openers are potent relaxants of mouse ileum. These observations are consistent with the existence of ATP-dependent K+ channels in murine intestinal muscle which, however, differ somewhat in properties from those reported for vascular muscle and pancreatic ,-cells. [source] High-resolution melt analysis for the detection of a mutation associated with permethrin resistance in a population of scabies mitesMEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2008C. PASAY Abstract Permethrin as a topical acaricide cream is widely used to treat scabies. The neuronal voltage-sensitive sodium channel (Vssc), necessary for the generation of action potentials in excitable cells, is the target of pyrethroid acaricides such as permethrin. Pyrethroid resistance has been linked to specific mutations in the Vssc gene. Following the partial sequencing of the Vssc gene in the scabies mite Sarcoptes scabiei (L.) (Astigmata: Sarcoptidae), we compared Vssc gene sequences from permethrin-sensitive and -tolerant S. scabiei var. canis Gerlach mites, and identified a G to A single nucleotide polymorphism (SNP) in permethrin-tolerant mites resulting in an amino acid change from glycine to aspartic acid in domain III S6. The mutation is in a region of the gene where mutations have been identified in a range of pyrethroid-resistant arthropods. Results of in vitro permethrin exposure assays showed that survival rates for mites bearing the mutation were similar to those previously reported for mites from human subjects where clinical tolerance to permethrin had been observed. A real-time polymerase chain reaction,high-resolution melt (PCR-HRM) assay was developed to detect this SNP. This assay provides a useful methodology for screening for this and other mutations associated with permethrin resistance in scabies mite populations and thus facilitates surveillance for acaricide resistance. [source] Manganese-enhanced magnetic resonance imaging (MEMRI)NMR IN BIOMEDICINE, Issue 8 2004Alan P. Koretsky Abstract Manganese ion (Mn2+) is an essential metal that participates as a cofactor in a number of critical biological functions, such as electron transport, detoxification of free radicals and synthesis of neurotransmitters. Mn2+ can enter excitable cells using some of the same transport systems as Ca2+ and it can bind to a number of intracellular sites because it has high affinity for Ca2+ and Mg2+ binding sites on proteins and nucleic acids. Paramagnetic forms of manganese ions are potent MRI relaxation agents. Indeed, Mn2+ was the first contrast agent proposed for use in MRI. Recently, there has been renewed interest in combining the strong MRI relaxation effects of Mn2+ with its unique biology, in order to further expand the already broad assortment of useful information that can be measured by MRI. Such an approach has been continuously developed in the past several years to provide unique tissue contrast, to assess tissue viability, to act as a surrogate marker of calcium influx into cells and to trace neuronal connections. This special issue of NMR in Biomedicine on manganese-enhanced MRI (MEMRI) is aimed at providing the readers of this journal with an extensive review of some of the most prominent applications of MEMRI in biological systems. Written by several of the leaders in the field, the reviews and original research articles featured in this special issue are likely to offer an exciting and inspiring view of the broad range of applications of MEMRI. Copyright © 2004 John Wiley & Sons, Ltd. [source] Apical SK potassium channels and Ca2+ -dependent anion secretion in endometrial epithelial cellsTHE JOURNAL OF PHYSIOLOGY, Issue 3 2008Melissa L. Palmer Apical uridine triphosphate (UTP) stimulation was shown to increase short circuit current (Isc) in immortalized porcine endometrial gland epithelial monolayers. Pretreatment with the bee venom toxin apamin enhanced this response. Voltage-clamp experiments using amphotericin B-permeablized monolayers revealed that the apamin-sensitive current increased immediately after UTP stimulation and was K+ dependent. The current,voltage relationship was slightly inwardly rectifying with a reversal potential of ,52 ± 2 mV, and the PK/PNa ratio was 14, indicating high selectivity for K+. Concentration,response relationships for apamin and dequalinium had IC50 values of 0.5 nm and 1.8 ,m, respectively, consistent with data previously reported for SK3 channels in excitable cells and hepatocytes. Treatment of monolayers with 50 ,m BAPTA-AM completely blocked the effects of UTP on K+ channel activation, indicating that the apamin-sensitive current was also Ca2+ dependent. Moreover, channel activation was blocked by calmidazolium (IC50= 5 ,m), suggesting a role for calmodulin in Ca2+ -dependent regulation of channel activity. RT-PCR experiments demonstrated expression of mRNA for the SK1 and SK3 channels, but not SK2 channels. Treatment of monolayers with 20 nm oestradiol-17, produced a 2-fold increase in SK3 mRNA, a 2-fold decrease in SK1 mRNA, but no change in GAPDH mRNA expression. This result correlated with a 2.5-fold increase in apamin-sensitive K+ channel activity in the apical membrane. We speculate that SK channels provide a mechanism for rapidly sensing changes in intracellular Ca2+ near the apical membrane, evoking immediate hyperpolarization necessary for increasing the driving force for anion efflux following P2Y receptor activation. [source] Subtype-selective targeting of voltage-gated sodium channelsBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2009Steve England Voltage-gated sodium channels are key to the initiation and propagation of action potentials in electrically excitable cells. Molecular characterization has shown there to be nine functional members of the family, with a high degree of sequence homology between the channels. This homology translates into similar biophysical and pharmacological properties. Confidence in some of the channels as drug targets has been boosted by the discovery of human mutations in the genes encoding a number of them, which give rise to clinical conditions commensurate with the changes predicted from the altered channel biophysics. As a result, they have received much attention for their therapeutic potential. Sodium channels represent well-precedented drug targets as antidysrhythmics, anticonvulsants and local anaesthetics provide good clinical efficacy, driven through pharmacology at these channels. However, electrophysiological characterization of clinically useful compounds in recombinant expression systems shows them to be weak, with poor selectivity between channel types. This has led to the search for subtype-selective modulators, which offer the promise of treatments with improved clinical efficacy and better toleration. Despite developments in high-throughput electrophysiology platforms, this has proven very challenging. Structural biology is beginning to offer us a greater understanding of the three-dimensional structure of voltage-gated ion channels, bringing with it the opportunity to do real structure-based drug design in the future. This discipline is still in its infancy, but developments with the expression and purification of prokaryotic sodium channels offer the promise of structure-based drug design in the not too distant future. [source] | |||||||||||||