Abstract 16515: Differential Functions of HCN1 and HCN4 Pacemaker Channels Within the Sinoatrial Node for the Stable and Precise Beating of the Heart

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Stefanie Fenske ◽  
Vanessa Marks ◽  
Stefanie Koenigsbauer ◽  
Sami I Hassan ◽  
Tilman Ziegler ◽  
...  
Keyword(s):  
Heart Rate ◽  
Mouse Models ◽  
Sinoatrial Node ◽  
Critical Role ◽  
Functional Characterization ◽  
Heart Beat ◽  
Fine Tuning ◽  
Hcn Channels ◽  
Pacemaker Cells

The heart beat is initiated by the generation of spontaneous action potentials in pacemaker cells of the sinoatrial node (SAN) region. The maintenance of a stable heart beat requires mechanisms which protect the SAN pacemaker cells from potential perturbing influences which arise from inside and outside the sinoatrial network. Our previous work suggests that the hyperpolarization-activated cyclic nucleotide gated channel subtype 1 (HCN1) protects against such perturbations and thereby increases the stability, the precision and the safety of the sinoatrial network. Here, we investigate the role of HCN4 channels within this context. Using genetic mouse models deficient for HCN channels as well as mouse models expressing engineered HCN channels, we performed a detailed functional characterization of pacemaker mechanisms in single isolated sinoatrial node cells, explanted beating sinoatrial node preparations, with telemetric in vivo electrocardiography, echocardiography, and in vivo electrophysiology. We provide evidence that HCN4 has a critical role in counteracting and balancing potentially destabilizing effects of the autonomic nervous system on the regulation of the heart rate. Specifically, HCN4 channels smooth the transition of the heart rate to a new equilibrium. Furthermore, we provide evidence that the cAMP- dependent fine tuning of HCN4 channel activity could provide the exact dosage of current to balance and counteract overshooting responses of the heart rate to autonomic regulation. In the absence of such a protecting effect, mice display a brady- tachy syndrome.

scholarly journals Direct Negative Chronotropic Action of Desflurane on Sinoatrial Node Pacemaker Activity in the Guinea Pig Heart

2014 ◽  
Vol 120 (6) ◽  
pp. 1400-1413 ◽  
Author(s):  
Akiko Kojima ◽  
Yuki Ito ◽  
Hirotoshi Kitagawa ◽  
Hiroshi Matsuura ◽  
Shuichi Nosaka
Keyword(s):  
Heart Rate ◽  
Action Potentials ◽  
Inhibitory Action ◽  
Sinoatrial Node ◽  
Ionic Currents ◽  
Pacemaker Cells ◽  
Chronotropic Action ◽  
Perfused Hearts ◽  
Sinoatrial Node Automaticity

Abstract Background: Desflurane inhalation is associated with sympathetic activation and concomitant increase in heart rate in humans and experimental animals. There is, however, little information concerning the direct effects of desflurane on electrical activity of sinoatrial node pacemaker cells that determines the intrinsic heart rate. Methods: Whole-cell patch-clamp experiments were conducted on guinea pig sinoatrial node pacemaker cells to record spontaneous action potentials and ionic currents contributing to sinoatrial node automaticity, namely, hyperpolarization-activated cation current (If), T-type and L-type Ca2+ currents (ICa,T and ICa,L, respectively), Na+/Ca2+ exchange current (INCX), and rapidly and slowly activating delayed rectifier K+ currents (IKr and IKs, respectively). Electrocardiograms were recorded from ex vivo Langendorff-perfused hearts and in vivo hearts. Results: Desflurane at 6 and 12% decreased spontaneous firing rate of sinoatrial node action potentials by 15.9% (n = 11) and 27.6% (n = 10), respectively, which was associated with 20.4% and 42.5% reductions in diastolic depolarization rate, respectively. Desflurane inhibited If, ICa,T, ICa,L, INCX, and IKs but had little effect on IKr. The negative chronotropic action of desflurane was reasonably well reproduced in sinoatrial node computer model. Desflurane reduced the heart rate in Langendorff-perfused hearts. High concentration (12%) of desflurane inhalation was associated with transient tachycardia, which was totally abolished by pretreatment with the β-adrenergic blocker propranolol. Conclusions: Desflurane has a direct negative chronotropic action on sinoatrial node pacemaking activity, which is mediated by its inhibitory action on multiple ionic currents. This direct inhibitory action of desflurane on sinoatrial node automaticity seems to be counteracted by sympathetic activation associated with desflurane inhalation in vivo.

scholarly journals Neuron-class specific responses govern adaptive remodeling of myelination in the neocortex

2020 ◽  
Author(s):  
Sung Min Yang ◽  
Katrin Michel ◽  
Vahbiz Jokhi ◽  
Elly Nedivi ◽  
Paola Arlotta
Keyword(s):  
Critical Role ◽  
Sensory Experience ◽  
Monocular Deprivation ◽  
Fine Tuning ◽  
Initial Increase ◽  
Projection Neurons ◽  
Myelin Sheaths ◽  
Adaptive Circuit ◽  
Callosal Projection

AbstractMyelination plasticity plays a critical role in neurological function, including learning and memory. However, it is unknown whether this plasticity is enacted through uniform changes across all neuronal subtypes, or whether myelin dynamics vary between neuronal classes to enable fine-tuning of adaptive circuit responses. We performed in vivo two-photon imaging to investigate the dynamics of myelin sheaths along single axons of both excitatory callosal projection neurons and inhibitory parvalbumin+ interneurons in layer 2/3 of adult mouse visual cortex. We find that both neuron types show dynamic, homeostatic myelin remodeling under normal vision. However, monocular deprivation results in experience-dependent adaptive myelin remodeling only in parvalbumin+ interneurons, but not in callosal projection neurons. Monocular deprivation induces an initial increase in elongation events in myelin segments of parvalbumin+ interneurons, followed by a contraction phase affecting a separate cohort of segments. Sensory experience does not alter the generation rate of new myelinating oligodendrocytes, but can recruit pre-existing oligodendrocytes to generate new myelin sheaths. Parvalbumin+ interneurons also show a concomitant increase in axonal branch tip dynamics independent from myelination events. These findings suggest that adaptive myelination is part of a coordinated suite of circuit reconfiguration processes, and demonstrate that distinct classes of neocortical neurons individualize adaptive remodeling of their myelination profiles to diversify circuit tuning in response to sensory experience.

Dynamic regulation of the voltage-gated Kv2.1 potassium channel by multisite phosphorylation

2007 ◽  
Vol 35 (5) ◽  
pp. 1064-1068 ◽  
Author(s):  
D.P. Mohapatra ◽  
K.-S. Park ◽  
J.S. Trimmer
Keyword(s):  
Neuronal Excitability ◽  
Critical Role ◽  
Functional Characterization ◽  
K Channel ◽  
Delayed Rectifier ◽  
Dynamic Regulation ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
Specific Regulation

Voltage-gated K+ channels are key regulators of neuronal excitability. The Kv2.1 voltage-gated K+ channel is the major delayed rectifier K+ channel expressed in most central neurons, where it exists as a highly phosphorylated protein. Kv2.1 plays a critical role in homoeostatic regulation of intrinsic neuronal excitability through its activity- and calcineurin-dependent dephosphorylation. Here, we review studies leading to the identification and functional characterization of in vivo Kv2.1 phosphorylation sites, a subset of which contribute to graded modulation of voltage-dependent gating. These findings show that distinct developmental-, cell- and state-specific regulation of phosphorylation at specific sites confers a diversity of functions on Kv2.1 that is critical to its role as a regulator of intrinsic neuronal excitability.

scholarly journals Functional Characterization of Brain Tumor-Initiating Cells: Implications for Preclinical Models and Drug Development

Neurosurgery ◽  
2019 ◽  
Vol 66 (Supplement_1) ◽  
Author(s):  
Cesar A Garcia ◽  
Adip Guruprasad Bhargav ◽  
Sujan K Mondal ◽  
Karim ReFaey ◽  
Natanael Zarco ◽  
...  
Keyword(s):  
Brain Tumor ◽  
Critical Role ◽  
Functional Characterization ◽  
Tumor Initiating Cells ◽  
Retroviral Transduction ◽  
Significant Difference ◽  
Brain Tumor Initiating Cells ◽  
Functional Features

Abstract INTRODUCTION Glioblastoma (GBM) is the deadliest and most common primary brain cancer in adults. Brain tumor-initiating cells (BTICs) are a heterogeneous subset of stem-like, invasive cells that play a critical role in treatment failure and recurrence. METHODS Here, we propose a system to functionally characterize patient-derived BTICs to identify features that will guide assessment of therapeutics in a BTIC subpopulation-specific manner. We established and evaluated 5 BTIC populations based on (1) proliferation, (2) stemness, (3) migration, (4) tumorigenesis, (5) clinical characteristics, and (6) therapeutic sensitivity. RESULTS Overall, in Vitro growth trends reflected in Vivo growth rates. However, a significant difference was found between tumor growth in male versus female mice in 3 BTIC lines (QNS108 P = .0011; QNS120 P < .0001; QNS 140 P < .0001). Differences in survival were observed, where BTICs derived from male and female patients produced faster morbidity in mice of the opposite sex (male derived QNS108 male vs female P = .0039; female derived QNS203 male vs female P = .029). QNS203, which was isolated from a tumor in contact with the anterior subventricular zone, decreased survival at a faster rate compared to other cell lines (n = 10 per line, 5 males/5 females, P < .0001). Stem-like properties of BTICs were assessed via differentiation marker expression, sphere-forming capacity, and detection of canonical marker CD133. Higher CD133 expression correlated with faster in Vitro doubling time and greater tumor burden. Histology reflected similar patient tumor features such as migration across the corpus callosum and cystic formation. BTICs revealed varying responses to therapies (TMZ, Radiation, TRAIL, BMP4) and varied competence to retroviral transduction. CONCLUSION By studying the functional features of BTICs within our model of GBM heterogeneity, it was shown that several factors influenced tumorigenesis and survival. These included original tumor location, stemness, variation in therapeutic sensitivity, and a critical finding for the role of sex, an unexplored area for creating next-generation, sex-specific, and BTIC-specific therapeutics.

scholarly journals Modulation of root growth by nutrient-defined fine-tuning of polar auxin transport

2020 ◽  
Author(s):  
Krisztina Ötvös ◽  
Marco Marconi ◽  
Andrea Vega ◽  
Jose O’ Brien ◽  
Alexander Johnson ◽  
...  
Keyword(s):  
Root Growth ◽  
Nitrogen Source ◽  
Critical Role ◽  
Primary Root ◽  
Dynamic Environment ◽  
Fine Tuning ◽  
Specific Cell ◽  
Post Translational Modification ◽  
Available Nitrogen

AbstractNitrogen is an essential macronutrient and its availability in soil plays a critical role in plant growth, development and impacts agricultural productivity. Plants have evolved different strategies to sense and respond to heterogeneous nitrogen distribution. Modulating root system architecture, including primary root growth and branching, is among the most essential plant adaptions to ensure adequate nitrogen acquisition. However, the immediate molecular pathways coordinating the adjustment of root growth in response to varying nitrogen sources are poorly understood. Here, using a combination of physiological, live in vivo high- and super resolution imaging, we describe a novel adaptation strategy of root growth on available nitrogen source. We show that growth, i.e. tissue-specific cell division and elongation rates are fine-tuned by modulating auxin flux within and between tissues. Changes in auxin redistribution are achieved by nitrogen source dependent post-translational modification of PIN2, a major auxin efflux carrier, at an uncharacterized, evolutionary conserved phosphosite. Further, we generate a computer model based on our results which successfully recapitulate our experimental observations and creates new predictions that could broaden our understanding of root growth mechanisms in the dynamic environment.

Autonomic control of heart rate exhibits diurnal shifts in a crocodilian

2008 ◽  
Vol 29 (4) ◽  
pp. 567-571 ◽  
Author(s):  
Mariana Micheli ◽  
Hamish Campbell
Keyword(s):  
Heart Rate ◽  
Cardiac Output ◽  
Body Temperature ◽  
Diurnal Cycle ◽  
Natural Habitat ◽  
Dorsal Surface ◽  
Heart Beat ◽  
Rate Of Change ◽  
Fine Tuning ◽  
Free Ranging

AbstractOver the diurnal cycle most reptiles show large changes in internal body temperature and heart rate (fH). The raising of fH, as the surface of a heliothermic reptile warms, increases cardiac output and facilitates in optimising the preferred daily body temperature (PDBT). In mammals, the fine tuning of cardiac output by the autonomic system can be observed through distinct oscillatory patterns in fH. This study examined Caiman latirostris (n = 6) to determine if similar oscillations in fH were present, and to assess if they exhibited a diurnal component associated with daily shifts in body temperature. A surgically implanted miniature datalogger recorded every heart beat and the dorsal surface temperature (Tds) of animals free-ranging in a semi-natural habitat. All C. latirostris exhibited rapid warming of Tds between 0700 and 1200. This was correlated with a rapid increase in fH, accompanied by erratic beat-to-beat oscillations in instantaneous fH. As Tds cooled, fH decreased and the short-term oscillations were abolished, resulting in a much slower rate of change in instantaneous fH. The two distinct fH rhythms may serve to optimise the PDBT over the diurnal cycle.

Gene-targeting and transgenic approaches to IGF and IGF binding protein function

1995 ◽  
Vol 269 (4) ◽  
pp. E613-E622 ◽  
Author(s):  
T. L. Wood
Keyword(s):  
Mouse Models ◽  
Protein Function ◽  
Binding Proteins ◽  
Germ Line ◽  
Critical Role ◽  
Somatic Growth ◽  
Igf Binding Proteins ◽  
Igf Binding ◽  
Mouse Lines

The ability to manipulate genetic information in the germ line of mice has provided powerful approaches to study gene function in vivo. These approaches have included the establishment of mouse lines in which a specified gene or genes are overexpressed, ectopically expressed, or deleted. Transgenic and gene-targeted mouse lines have been used extensively to study the function of the insulin-like growth factors (IGF), IGF-I and IGF-II, and their receptors and binding proteins. In the IGF system, these technologies have elucidated the roles of the IGFs in fetal and somatic growth and have demonstrated a critical role for this system in transformation and tumorigenesis. Analysis of combinatorial crosses of gene-targeted mouse lines also has suggested the existence of an as yet unidentified IGF receptor that regulates fetal growth. Similar approaches using transgenic and gene-targeted mouse models have been initiated to study the in vivo functions of the IGF binding proteins. These mouse models provide important tools to test specific functional questions in vivo as well as to study the long-term physiological consequences of chronic gene alterations.

Functional characterization of LePGT1, a membrane-bound prenyltransferase involved in the geranylation of p-hydroxybenzoic acid

2009 ◽  
Vol 421 (2) ◽  
pp. 231-241 ◽  
Author(s):  
Kazuaki Ohara ◽  
Ayumu Muroya ◽  
Nobuhiro Fukushima ◽  
Kazufumi Yazaki
Keyword(s):  
Molecular Model ◽  
Substrate Binding ◽  
Expression System ◽  
Critical Role ◽  
Functional Characterization ◽  
Site Directed Mutagenesis ◽  
Hydroxybenzoic Acid ◽  
Membrane Bound

The AS-PT (aromatic substrate prenyltransferase) family plays a critical role in the biosynthesis of important quinone compounds such as ubiquinone and plastoquinone, although biochemical characterizations of AS-PTs have rarely been carried out because most members are membrane-bound enzymes with multiple transmembrane α-helices. PPTs [PHB (p-hydroxybenzoic acid) prenyltransferases] are a large subfamily of AS-PTs involved in ubiquinone and naphthoquinone biosynthesis. LePGT1 [Lithospermum erythrorhizon PHB geranyltransferase] is the regulatory enzyme for the biosynthesis of shikonin, a naphthoquinone pigment, and was utilized in the present study as a representative of membrane-type AS-PTs to clarify the function of this enzyme family at the molecular level. Site-directed mutagenesis of LePGT1 with a yeast expression system indicated three out of six conserved aspartate residues to be critical to the enzymatic activity. A detailed kinetic analysis of mutant enzymes revealed the amino acid residues responsible for substrate binding were also identified. Contrary to ubiquinone biosynthetic PPTs, such as UBIA in Escherichia coli which accepts many prenyl substrates of different chain lengths, LePGT1 can utilize only geranyl diphosphate as its prenyl substrate. Thus the substrate specificity was analysed using chimeric enzymes derived from LePGT1 and UBIA. In vitro and in vivo analyses of the chimeras suggested that the determinant region for this specificity was within 130 amino acids of the N-terminal. A 3D (three-dimensional) molecular model of the substrate-binding site consistent with these biochemical findings was generated.

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