scholarly journals On the role of transient depolarization-activated K+ current in microvillar photoreceptors

2018 ◽  
Vol 150 (9) ◽  
pp. 1287-1298 ◽  
Author(s):  
Roman V. Frolov
Keyword(s):  
Information Transfer ◽  
Gaussian White Noise ◽  
Resting Potential ◽  
Delayed Rectifier ◽  
Channel Blockers ◽  
Large Set ◽  
Wild Type ◽  
Shaker Channels ◽  
Dim Light

Photoreceptors in the compound eyes of most insect species express two functional types of depolarization-activated potassium currents: a transient A-type current (IA) and a sustained delayed rectifier current (IDR). The role of Shaker-dependent IA in Drosophila melanogaster photoreceptors was previously investigated by comparing intracellular recordings from Shaker and wild-type photoreceptors. Shaker channels were proposed to be involved in low-frequency signal amplification in dim light and reduction of the metabolic cost of information transfer. Here, I study the function of IA in photoreceptors of the cockroach Panchlora nivea using the patch-clamp method. Responses to Gaussian white-noise stimuli reveal that blockade of IA with 4-aminopyridine has no discernible effect on voltage responses or information processing. However, because open-channel blockers are often ineffective at low membrane potentials, no conclusion on the role of IA could be made on the basis of negative results of pharmacological tests. Using a relatively large set of control data, a physiological variability analysis was performed to discern the role of IA. Amplitudes of the IA window current and half-activation potentials correlate strongly with membrane corner frequencies, especially in dim light, indicating that IA facilitates transmission of higher frequencies. Consistent with voltage-dependent inactivation of IA, these correlations decrease with depolarization in brighter backgrounds. In contrast, correlations involving IDR are comparatively weak. Upon reexamining photoreceptor conductance in wild-type and Shaker strains of D. melanogaster, I find a biphasic voltage dependence near the resting potential in a minority of photoreceptors from both strains, indicating that Shaker channels are not crucial for early amplification of voltage signals in D. melanogaster photoreceptors. Leak current in Shaker photoreceptors at the level of the soma is not elevated. These results suggest a novel role for IA in facilitating transmission of high-frequency signals in microvillar photoreceptors.

Functional Changes in Genetically Dysmyelinated Spinal Cord Axons of Shiverer Mice: Role of Juxtaparanodal Kv1 Family K+ Channels

2006 ◽  
Vol 95 (3) ◽  
pp. 1683-1695 ◽  
Author(s):  
Kusum Sinha ◽  
Soheila Karimi-Abdolrezaee ◽  
Alexander A. Velumian ◽  
Michael G. Fehlings
Keyword(s):  
Spinal Cord ◽  
Western Blotting ◽  
Neurological Deficits ◽  
Channel Blockers ◽  
Wild Type ◽  
Functional Changes ◽  
Cord Injury ◽  
Compound Action Potentials ◽  
Axonal Dysfunction

Axonal dysfunction after spinal cord injury (SCI) and other types of neurotrauma is associated with demyelination and exposure of juxtaparanodal K+ channels. In this study, sucrose gap electrophysiology using selective and nonselective K+ channel blockers, confocal immunohistochemistry, and Western blotting were used to study the role of Kv1.1 and Kv1.2 K+ channel subunits in dysmyelination-induced spinal cord axonal dysfunction in s hiverer mice, which lack the gene encoding myelin basic protein (MBP) and exhibit incomplete myelin sheath formation on CNS axons. The s hiverer spinal cord axons exhibited smaller amplitude of compound action potentials (CAPs), reduced conduction velocity, reduced excitability, and greater degree of high-frequency conduction failure. The “fast” K+ channel blocker 4-aminopyridine, the toxin DTX-I, which targets the Kv1.1 and Kv1.2, but not DTX- K, which has higher selectivity for Kv1.1, increased the amplitude and area of CAPs of shiverer mice spinal cord axons but had insignificant effects in wild-type mice. Confocal immunohistochemistry showed that, unlike wild-type mice, which have a precise juxtaparanodal localization of the Kv1.l and Kv1.2 K+ channel subunits, shiverer mouse axons displayed a dispersed distribution of these subunits along the internodes. In contrast, the Kv1.l and Kv1.2 subunits, Na+ channels remained highly localized to the nodal regions. Western blotting showed an increased expression of Kv 1.1 and 1.2 in the shiverer mouse spinal cord. These results provide evidence that the neurological deficits associated with myelin deficiency reflect the altered distribution and expression of the K+ channel subunits Kv1.l and Kv1.2 along the internodes of spinal cord axons associated with the biophysical consequences caused by alterations in the myelin sheaths.

scholarly journals Sodium uptake and membrane excitation in Paramecium.

1979 ◽  
Vol 81 (2) ◽  
pp. 374-381 ◽  
Author(s):  
H G Hansma
Keyword(s):  
Resting Potential ◽  
Wild Type ◽  
Sodium Uptake ◽  
Membrane Excitation ◽  
Kinetics Of ◽  
Na Uptake ◽  
Potential Level

Although the phenotypes of many membrane-excitation mutants of Paramecium are best expressed in Na+-containing solutions, little is known about the role of Na+ in membrane excitation in Paramecium. By measuring 22Na fluxes, we have shown that: (a) The total cellular Na+ content is equivalent to a cytoplasmic concentration of 3--4 mM, if the Na+ concentration is uniform throughout the cell. (b) The kinetics of Na+ uptake can be divided into a saturable Na+ uptake with an apparent Km = 0.15 mM and a nonsaturable Na+ uptake seen at higher Na+ concentrations up to 20 mM. (c) The rate of Na+ uptake in high Na+ solutions is correlated with the duration of backward swimming and membrane excitation in wild type Paramecium and the mutants fast-2 and paranoiac. (d) Na+ uptake is inhibited at 4 degrees C. From these results, we postulate that Na+ uptake is faster when the membrane is depolarized than when it is at the resting potential level.

scholarly journals Information Length Analysis of Linear Autonomous Stochastic Processes

Entropy ◽  
2020 ◽  
Vol 22 (11) ◽  
pp. 1265
Author(s):  
Adrian-Josue Guel-Cortez ◽  
Eun-jin Kim
Keyword(s):  
Stochastic Processes ◽  
Particle System ◽  
Gaussian White Noise ◽  
Information Geometry ◽  
Natural Oscillation ◽  
Large Set ◽  
Promising Tool ◽  
Long Time ◽  
Length Analysis

When studying the behaviour of complex dynamical systems, a statistical formulation can provide useful insights. In particular, information geometry is a promising tool for this purpose. In this paper, we investigate the information length for n-dimensional linear autonomous stochastic processes, providing a basic theoretical framework that can be applied to a large set of problems in engineering and physics. A specific application is made to a harmonically bound particle system with the natural oscillation frequency ω, subject to a damping γ and a Gaussian white-noise. We explore how the information length depends on ω and γ, elucidating the role of critical damping γ=2ω in information geometry. Furthermore, in the long time limit, we show that the information length reflects the linear geometry associated with the Gaussian statistics in a linear stochastic process.

scholarly journals miR-183/96 plays a pivotal regulatory role in mouse photoreceptor maturation and maintenance

2017 ◽  
Vol 114 (24) ◽  
pp. 6376-6381 ◽  
Author(s):  
Lue Xiang ◽  
Xue-Jiao Chen ◽  
Kun-Chao Wu ◽  
Chang-Jun Zhang ◽  
Gao-Hui Zhou ◽  
...  
Keyword(s):  
Photoreceptor Cells ◽  
Fine Tuning ◽  
Wild Type ◽  
Double Knockout ◽  
Adeno Associated Virus ◽  
Functional Changes ◽  
In The Wild ◽  
Light Stimuli ◽  
Dim Light

MicroRNAs (miRNAs) are known to be essential for retinal maturation and functionality; however, the role of the most abundant miRNAs, the miR-183/96/182 cluster (miR-183 cluster), in photoreceptor cells remains unclear. Here we demonstrate that ablation of two components of the miR-183 cluster, miR-183 and miR-96, significantly affects photoreceptor maturation and maintenance in mice. Morphologically, early-onset dislocated cone nuclei, shortened outer segments and thinned outer nuclear layers are observed in the miR-183/96 double-knockout (DKO) mice. Abnormal photoreceptor responses, including abolished photopic electroretinography (ERG) responses and compromised scotopic ERG responses, reflect the functional changes in the degenerated retina. We further identify Slc6a6 as the cotarget of miR-183 and miR-96. The expression level of Slc6a6 is significantly higher in the DKO mice than in the wild-type mice. In contrast, Slc6a6 is down-regulated by adeno-associated virus-mediated overexpression of either miR-183 or miR-96 in wild-type mice. Remarkably, both silencing and overexpression of Slc6a6 in the retina are detrimental to the electrophysiological activity of the photoreceptors in response to dim light stimuli. We demonstrate that miR-183/96–mediated fine-tuning of Slc6a6 expression is indispensable for photoreceptor maturation and maintenance, thereby providing insight into the epigenetic regulation of photoreceptors in mice.

scholarly journals Global genetic deletion of CaV3.3 channels facilitates anaesthetic induction and enhances isoflurane-sparing effects of T-type calcium channel blockers

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Simon Feseha ◽  
Tamara Timic Stamenic ◽  
Damon Wallace ◽  
Caesare Tamag ◽  
Lingling Yang ◽  
...  
Keyword(s):  
Channel Blocker ◽  
Mutant Mice ◽  
Channel Blockers ◽  
Volatile Anaesthetics ◽  
Wild Type ◽  
Anaesthetic Induction ◽  
Knock Out ◽  
Valuable Adjunct ◽  
Genetic Deletion

AbstractWe previously documented that the CaV3.3 isoform of T-type calcium channels (T-channels) is inhibited by clinically relevant concentrations of volatile anaesthetics, including isoflurane. However, little is understood about the functional role of CaV3.3 channels in anaesthetic-induced hypnosis and underlying neuronal oscillations. To address this issue, we used CaV3.3 knock-out (KO) mice and a panselective T-channel blocker 3,5-dichloro-N-[1-(2,2-dimethyltetrahydro-pyran-4-ylmethyl)-4-fluoro-piperidin-4-ylmethyl]-benzamide (TTA-P2). We found that mutant mice injected with the vehicle showed faster induction of hypnosis than wild-type (WT) mice, while the percent isoflurane at which hypnosis and immobility occurred was not different between two genotypes. Furthermore, we found that TTA-P2 facilitated isoflurane induction of hypnosis in the CaV3.3 KO mice more robustly than in the WT mice. Isoflurane-induced hypnosis following injections of TTA-P2 was accompanied with more prominent delta and theta EEG oscillations in the mutant mice, and reached burst-suppression pattern earlier when compared to the WT mice. Our findings point to a relatively specific value of CaV3.3 channels in anaesthetic induced hypnosis. Furthermore, we propose that T-channel blockers may be further explored as a valuable adjunct to reducing the usage of potent volatile anaesthetics, thereby improving their safety.

Differential Role of Components of the Fibrinolytic System in the Formation and Removal of Thrombus Induced by Endothelial Injury

1999 ◽  
Vol 81 (04) ◽  
pp. 601-604 ◽  
Author(s):  
Hiroyuki Matsuno ◽  
Osamu Kozawa ◽  
Masayuki Niwa ◽  
Shigeru Ueshima ◽  
Osamu Matsuo ◽  
...  
Keyword(s):  
Plasminogen Activator ◽  
Thrombus Formation ◽  
Endothelial Injury ◽  
Fibrinolytic System ◽  
Tissue Type ◽  
Clot Lysis ◽  
Wild Type ◽  
Type Plasminogen Activator ◽  
Pai 1

SummaryThe role of fibrinolytic system components in thrombus formation and removal in vivo was investigated in groups of six mice deficient in urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA), or plasminogen activator inhibitor-1 (PAI-1) (u-PA-/-, t-PA-/- or PAI-1-/-, respectively) or of their wild type controls (u-PA+/+, t-PA+/+ or PAI-1+/+). Thrombus was induced in the murine carotid artery by endothelial injury using the photochemical reaction between rose bengal and green light (540 nm). Blood flow was continuously monitored for 90 min on day 0 and for 20 min on days 1, 2 and 3. The times to occlusion after the initiation of endothelial injury in u-PA+/+, t-PA+/+ or PAI-1+/+ mice were 9.4 ± 1.3, 9.8 ± 1.1 or 9.7 ± 1.6 min, respectively. u-PA-/- and t-PA-/- mice were indistinguishable from controls, whereas that of PAI-1-/- mice were significantly prolonged (18.4 ± 3.7 min). Occlusion persisted for the initial 90 min observation period in 10 of 18 wild type mice and was followed by cyclic reflow and reocclusion in the remaining 8 mice. At day 1, persistent occlusion was observed in 1 wild type mouse, 8 mice had cyclic reflow and reocclusion and 9 mice had persistent reflow. At day 2, all injured arteries had persistent reflow. Persistent occlusion for 90 min on day 0 was observed in 3 u-PA-/-, in all t-PA-/- mice at day 1 and in 2 of the t-PA-/-mice at day 2 (p <0.01 versus wild type mice). Persistent patency was observed in all PAI-1-/- mice at day 1 and in 5 of the 6 u-PA-/- mice at day 2 (both p <0.05 versus wild type mice). In conclusion, t-PA increases the rate of clot lysis after endothelial injury, PAI-1 reduces the time to occlusion and delays clot lysis, whereas u-PA has little effect on thrombus formation and spontaneous lysis.

NATURAL SCIENTISTS AND RUSSIAN SCIENTIFIC FILMMAKING IN THE PRE-REVOLUTIONARY PERIOD (SCIENCE DIVISION OF THE A.A. KHANZHONKOV COMPANY)

2020 ◽  
Vol 42 (3) ◽  
pp. 355-368
Author(s):  
YEVGENIY ALEKSANDROV
Keyword(s):  
Information Transfer ◽  
Delayed Reaction ◽  
Russian Scientific ◽  
Physical Problems ◽  
Education Community ◽  
Future System ◽  
The Future ◽  
The Spectator ◽  
Revolutionary Period

The aim of the article is to recall the fi steps of comprehension by the scientific community of possibilities of a newly born means of the reality reflection. The means was initially oriented for obtaining reliable information and supposing a delayed reaction of the spectator in the process of communication. Recollection and understanding become more important under the distance education condition. Pre-revolutionary Russia lived anticipating changes, and the filmmaking was considered by the society as one of those progressive phenomena evidencing the coming of a new age. The scientists’ activity during the development of scientific fi in pre-revolutionary Russia was long hushed up and wasn’t considered as forming a basis for the future system of educational audio-visual communication. In this process there participated striking, creative personalities, mostly belonged to the community of Imperial Moscow University, which activity was during the age of changes. The significant contribution of pleiad of eminent scientists’ activity to the new direction formation was a reason to unify in one paper both their whole professional life data and information about their time-limited period of scientific fi In the future a more profound study of their achievements are considered to be promising. In the introduction the anterior period of the Russian fi appearance, where the scientific and education community of Russia was exploring the possibilities of a new means of information transfer for education purposes, is considered. Two main units are dedicated to the role of scientists in the development of scientific filmmaking for research and popularization of biomedical and physical problems.

Role of Ca2+ and Na+ on luteinizing hormone release from the calf pituitary

1988 ◽  
Vol 255 (4) ◽  
pp. E469-E474
Author(s):  
J. P. Kile ◽  
M. S. Amoss
Keyword(s):  
Luteinizing Hormone ◽  
Ionophore A23187 ◽  
Channel Blockers ◽  
Hormone Release ◽  
Primary Cells ◽  
Rat Pituitary ◽  
Voltage Dependent ◽  
Lh Release ◽  
Ca2 Channels

It has been proposed that gonadotropin-releasing hormone (GnRH) stimulates Ca2+ entry by activation of voltage-independent, receptor-mediated Ca2+ channels in the rat gonadotroph. Little work has been done on the role of calcium in GnRH-induced luteinizing hormone (LH) release in species other than the rat. Therefore, this study was done to compare the effects of agents that alter Ca2+ or Na+ entry on LH release from calf anterior pituitary primary cells in culture. GnRH (100 ng/ml), Ca2+ ionophore A23187 (2.5 microM), and the depolarizing agent ouabain (0.1-10 microM) all produced significant increases (P less than 0.05) in LH release; these effects were significantly reduced when the cells were preincubated with the organic Ca2+ channel blockers nifedipine (1-10 microM) and verapamil (1-10 microM) and with Co2+ (0.01-1 mM). The effect of ouabain was inhibited by tetrodotoxin (TTX; 1-10 nM) as well as by nifedipine at 0.1-10 microM. In contrast to its effect on rat pituitary LH release, TTX significantly inhibited GnRH-stimulated LH release at 1-100 nM. These results suggest that GnRH-induced LH release may employ Ca2+ as a second messenger in bovine gonadotrophs and support recent speculation that GnRH-induced Ca2+ mobilization may in part be voltage dependent.

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