PROPERTIES OF 185TAGE-ACTIVATED IONIC CURRENTS IN CELLS FROM THE BRAINS OF THE TRICLAD FLATWORM BDELLOURA CANDIDA

1993 ◽  
Vol 185 (1) ◽  
pp. 267-286
Author(s):  
K. L. Blair ◽  
P. A. V. Anderson
Keyword(s):  
Cultured Cells ◽  
Sodium Current ◽  
Cell Voltage ◽  
Ionic Currents ◽  
Sodium Currents ◽  
Channel Evolution ◽  
Major Stage ◽  
Fast Transient ◽  
State Component

Cells were dispersed from the brains of the triclad flatworm Bdelloura candida and maintained in primary culture for up to 2 weeks. Cultured cells assumed a variety of morphologies consistent with those of neurones in vivo. Whole-cell voltage-clamp recordings from cultured cells revealed that these cells possess a variety of ionic currents, including a fast transient sodium current, a calcium current and several potassium currents. The sodium current does not inactivate completely but instead decays to a steady-state component which has the same physiology and pharmacology as the fast transient component, suggesting that the two components are carried by the same population of channels. The physiology and pharmacology of these various currents were not remarkable save for the fact that, contrary to earlier reports, all sodium currents examined were sensitive to tetrodotoxin (TTX). These animals are, therefore, the lowest animals known to possess TTX-sensitive sodium currents and, as such, represent a major stage in sodium channel evolution.

Sodium Currents in Neurons From the Rostroventrolateral Medulla of the Rat

2003 ◽  
Vol 90 (3) ◽  
pp. 1635-1642 ◽  
Author(s):  
Ilya A. Rybak ◽  
Krzysztof Ptak ◽  
Natalia A. Shevtsova ◽  
Donald R. McCrimmon
Keyword(s):  
Sodium Channels ◽  
Sodium Current ◽  
Cell Voltage ◽  
Kinetic Properties ◽  
Persistent Sodium Current ◽  
Sodium Currents ◽  
Bötzinger Complex ◽  
Window Current ◽  
Bursting Activity

Rapidly inactivating and persistent sodium currents have been characterized in acutely dissociated neurons from the area of rostroventrolateral medulla that included the pre-Bötzinger Complex. As demonstrated in many studies in vitro, this area can generate endogenous rhythmic bursting activity. Experiments were performed on neonate and young rats (P1-15). Neurons were investigated using the whole cell voltage-clamp technique. Standard activation and inactivation protocols were used to characterize the steady-state and kinetic properties of the rapidly inactivating sodium current. Slow depolarizing ramp protocols were used to characterize the noninactivating sodium current. The “window” component of the rapidly inactivating sodium current was calculated using mathematical modeling. The persistent sodium current was revealed by subtraction of the window current from the total noninactivating sodium current. Our results provide evidence of the presence of persistent sodium currents in neurons of the rat rostroventrolateral medulla and determine voltage-gated characteristics of activation and inactivation of rapidly inactivating and persistent sodium channels in these neurons.

Differences in voltage-dependent sodium currents exhibited by superficial and deep layer neurons of guinea pig entorhinal cortex

1994 ◽  
Vol 71 (5) ◽  
pp. 1986-1991 ◽  
Author(s):  
S. Fan ◽  
M. Stewart ◽  
R. K. Wong
Keyword(s):  
Guinea Pig ◽  
Entorhinal Cortex ◽  
Deep Layer ◽  
Sodium Current ◽  
Membrane Conductance ◽  
Cell Voltage ◽  
Superficial Layer ◽  
Peak Amplitude ◽  
Sodium Currents ◽  
Test Pulse

1. Sodium currents were studied using whole-cell voltage-clamp techniques in neurons acutely isolated from superficial (II/III) and deep (V/VI) layers of guinea pig entorhinal cortex. 2. Sodium currents were larger (peak amplitude) in superficial than in deep layer cells under the same conditions: -1939 +/- 780 (SD) pA (N = 6) versus -307 +/- 257 pA (N = 6). Specific membrane conductance was calculated to be 12.3 +/- 9.6 mS/cm2 for superficial layer cells and 1.4 +/- 0.9 mS/cm2 for deep layer cells. 3. Sodium currents could be activated in superficial layer cells from potentials as depolarized as -20 mV, whereas no significant currents could be activated in deep neurons from potentials more depolarized than about -50 mV. Using a protocol consisting of a 25-ms prepulse and a 20 ms test pulse, the inactivation curves for superficial layer cells were found to be shifted toward more depolarized potentials by an average of 15 mV (V50 = -59.8 +/- 3.8 mV compared with -75.7 +/- 12.0 mV for deep cells). This produced a region of overlap with the activation curves for superficial cells. 4. Over a range of about -50 to -20 mV in superficial layer cells, the region of overlap of the activation and inactivation curves, a sodium current could be activated, which did not fully inactivate during the test pulse (average peak amplitude: -89.5 +/- 48.7 pA; crossover voltage: -39.2 +/- 2.0 mV). Voltage steps to more depolarized potentials, outside the voltage “window”, permitted complete inactivation of the sodium current.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract 12627: I Na Remodeling and Conduction Deficits in a Murine Model of Human LMNA -R545H Mutation

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Adonis Z Wu ◽  
Cheng Wang ◽  
Katie Spoonamore ◽  
Thomas Everett ◽  
Zhenhui Chen ◽  
...  
Keyword(s):  
Recovery Time ◽  
De Novo ◽  
Sodium Current ◽  
Sinus Node ◽  
Cell Voltage ◽  
Mrna Levels ◽  
Hek 293 ◽  
293 Cells ◽  
Electrocardiogram Ecg

Introduction: We have identified a de novo mutation of LMNA ( LMNA -R545H) in a 34-year-old man with high-grade atrioventricular block. Studies in HEK-293 cells showed that LMNA -R545H reduced the amplitude and resulted in a shift in gating kinetics of the voltage-gated sodium current ( I Na ). These results have not been confirmed in cardiomyocytes. Hypothesis: (1) LMNA -R545H mutation replicates the electrocardiogram (ECG) phenotypes in vivo and (2) there is downregulation of I Na in cardiomyocytes. Methods: We used CRISPR/Cas9 to generate a knock-in mouse model with LMNA -R545H mutation. Isolated cardiomyocytes were used for whole-cell voltage-clamp studies of I Na . Results: Panel (A) shows P, PR, QTc intervals were significantly prolonged and the standard deviation (SD) of the RR intervals was increased during anesthesia in Lmna (R545H+/+) but not in Lmna (R545H+) mice compared with the wild-type control littermates (WT, N=5-8). In Langendorff perfused hearts, the sinus node recovery time (SNRT) and effective refractory period (ERP) were significantly prolonged in the Lmna (R545H+/+) compared with both WT and Lmna (R545H+) . Lmna (R545H+/+) cardiomyocytes showed decreased I Na current density (-20.1±2.3 pA/pF vs. -30.3±3.9 pA/pF, -40 mV, n=7-8, p<.05, Panel B) and prolonged the recovery time constant from I Na inactivation (τ, 36.3±2.2 ms vs. 22.9±1.6 ms, each n=5, p<.05, Panel C). There were no difference in Nav1.5 protein and mRNA levels between the Lmna (R545H+/+) and WT hearts. Conclusions: Homozygous LMNA -R545H mutation leads to reduced I Na , prolonged PR and QTc intervals, and increased sinus arrhythmias.

In Vivo NGF Deprivation Reduces SNS Expression and TTX-R Sodium Currents in IB4-Negative DRG Neurons

1999 ◽  
Vol 81 (2) ◽  
pp. 803-810 ◽  
Author(s):  
Jenny Fjell ◽  
Theodore R. Cummins ◽  
Kaj Fried ◽  
Joel A. Black ◽  
Stephen G. Waxman
Keyword(s):  
Sodium Channel ◽  
Current Density ◽  
Sodium Current ◽  
High Antibody ◽  
Sodium Currents ◽  
Drg Neurons ◽  
Adult Rats ◽  
Antibody Titers

In vivo NGF deprivation reduces SNS expression and TTX-R sodium currents in IB4-negative DRG neurons. Recent evidence suggests that changes in sodium channel expression and localization may be involved in some pathological pain syndromes. SNS, a tetrodotoxin-resistant (TTX-R) sodium channel, is preferentially expressed in small dorsal root ganglion (DRG) neurons, many of which are nociceptive. TTX-R sodium currents and SNS mRNA expression have been shown to be modulated by nerve growth factor (NGF) in vitro and in vivo. To determine whether SNS expression and TTX-R currents in DRG neurons are affected by reduced levels of systemic NGF, we immunized adult rats with NGF, which causes thermal hypoalgesia in rats with high antibody titers to NGF. DRG neurons cultured from rats with high antibody titers to NGF, which do not bind the isolectin IB4 (IB4−) but do express TrkA, were studied with whole cell patch-clamp and in situ hybridization. Mean TTX-R sodium current density was decreased from 504 ± 77 pA/pF to 307 ± 61 pA/pF in control versus NGF-deprived neurons, respectively. In comparison, the mean TTX-sensitive sodium current density was not significantly different between control and NGF-deprived neurons. Quantification of SNS mRNA hybridization signal showed a significant decrease in the signal in NGF-deprived neurons compared with the control neurons. The data suggest that NGF has a major role in the maintenance of steady-state levels of TTX-R sodium currents and SNS mRNA in IB4− DRG neurons in adult rats in vivo.

Palmitoyl carnitine modifies sodium currents and induces transient inward current in ventricular myocytes

1994 ◽  
Vol 266 (3) ◽  
pp. H1034-H1046 ◽  
Author(s):  
J. Wu ◽  
P. B. Corr
Keyword(s):  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Ionic Currents ◽  
Inward Current ◽  
Palmitoyl Carnitine ◽  
Transient Inward Current ◽  
Ventricular Cells ◽  
Current Voltage

Long-chain acylcarnitines increase within 2 min in ischemic myocardium in vivo and induce delayed afterdepolarizations (DADs) and complex oscillations of membrane potential in vitro. This study was performed to assess the ionic currents underlying these electrophysiological alterations in isolated rabbit ventricular cells using whole cell voltage-clamp procedures. Palmitoyl carnitine (10 microM, for 6-10 min) elicited a transient inward current (Iti) in the presence of blockade of Ca2+ and K+ channels. The effect of palmitoyl carnitine was reversible after washout (n = 6). The amplitude of Iti was dependent on the amplitude of the preceding depolarization step. Palmitoyl carnitine (10 microM, for > 2 min) also induced another inward current, which was activated spontaneously at potentials between -120 and -20 mV with a linear current-voltage relationship (1.0 +/- 0.1 nA at -80 mV). This current was abolished by replacing extracellular Na+ with tetraethylammonium chloride, indicating that Na+ was the charge carrier. Inactivation of this current was slow (gamma = 885.9 +/- 89.1 ms, n = 12) or incomplete, indicating the appearance of a slow-inactivating Na+ inward current [INa(s)]. Palmitoyl carnitine always induced INa(s) before the appearance of Iti. Intracellular ethylene glycol-bis(beta-amino-ethyl ether)-N,N,N',N'-tetraacetic acid (10 mM) abolished Iti but did not suppress INa(s) (n = 4), indicating that INa(s) was not activated by intracellular Ca2+ (Cai2+). Tetrodotoxin (10 microM) also decreased the amplitude of INa(s). Thus palmitoyl carnitine induces INa(s), which likely leads to an increase in Na+ influx, thereby eliciting an increase in Cai2+ via the Na(+)-Ca2+ exchanger and leading to the development of Iti, DADs, and triggered activity.

Isoproterenol, DBcAMP, and forskolin inhibit cardiac sodium current

1989 ◽  
Vol 256 (6) ◽  
pp. C1131-C1137 ◽  
Author(s):  
K. Ono ◽  
T. Kiyosue ◽  
M. Arita
Keyword(s):  
Ventricular Myocytes ◽  
Sodium Current ◽  
Cell Voltage ◽  
Ionic Currents ◽  
Na Channel ◽  
Intracellular Camp ◽  
Channel Blockers ◽  
H Infinity ◽  
Inactivation Curve ◽  
Gating Mechanism

We studied the effects of isoproterenol (ISP), dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP), and forskolin on the sodium current (INa) of guinea pig ventricular myocytes using the tight-seal, whole cell voltage-clamp method. The extracellular [Na+] [( Na+]o) was decreased to 60 mM by replacing NaCl with sucrose (temperature, 32-33 degrees C). Ionic currents other than Na+ were suppressed using appropriate channel blockers. Depolarizing clamp pulse (duration, 30 ms) was applied at a rate of 0.2 Hz from a holding potential of -80 mV. ISP (1 microM) decreased the peak INa by 34% from 6.1 +/- 1.9 (SD) nA (control) to 4.0 +/- 1.5 nA (n = 7). The inhibition was more prominent at less negative potentials and disappeared in the presence of a beta-blocker (10 microM atenolol). The effects of DBcAMP (1-5 mM) and forskolin (3 microM) mimicked those of ISP and depressed the peak INa reversibly. DBcAMP (5 mM) shifted the inactivation curve of INa [h infinity-membrane potential (Em) relationship] to a hyperpolarizing direction, by 3.4 +/- 0.8 mV (n = 5). These findings suggest that ISP inhibits the cardiac INa+, probably by altering the gating mechanism of the Na+ channel, and that the effect is secondary to the increased levels of intracellular cAMP, with possible acceleration of cAMP-dependent phosphorylation of the channel.

A cardiac-like sodium current in motor neurons of a jellyfish

1996 ◽  
Vol 76 (4) ◽  
pp. 2240-2249 ◽  
Author(s):  
N. G. Grigoriev ◽  
J. D. Spafford ◽  
J. Przysiezniak ◽  
A. N. Spencer
Keyword(s):  
Sodium Channels ◽  
Motor Neurons ◽  
Sodium Current ◽  
Cell Voltage ◽  
Inactivation Kinetics ◽  
Sodium Currents ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Channel Properties ◽  
Selection Of

1. Whole cell voltage-clamp recordings from isolated swimming motor neurons (SMNs) reveal a rapidly activating and inactivating sodium current. 2. Permeability ratios of PLi/PNa = 0.941 and P(guanidinium)/PNa = 0.124 were measured for the mediating channel, which was impermeable to rubidium. 3. The conductance/voltage and steady state inactivation curves are shifted in a depolarizing direction by approximately 45 mV relative to most neuronal sodium currents in higher animals. 4. Activation could be fitted with two exponents and maximal current peaked at 0.74 +/- 0.06 ms (mean +/- SD). 5. Inactivation could be fitted with fast (Tau 1 = 1.91 +/- 0.07 ms at +10 mV) and slow (Tau 2 = 11.65 +/- 0.55 ms at +10 mV) exponents. 6. Half-recovery from inactivation occurred slowly (52.6 +/- 2.9 ms). 7. A second class of identifiable neurons, "B" neurons, possesses a distinctly different population of sodium channels. they showed different inactivation kinetics and far more rapid recovery from inactivation (half-recovery < 5 ms). 8. We conclude that there was physiological diversification of sodium channels early in metazoan evolution and that there has been considerable cell-specific selection of channel properties.

scholarly journals Corticotropin-releasing factor increases Purkinje neuron excitability by modulating sodium, potassium, and Ih currents

2015 ◽  
Vol 114 (6) ◽  
pp. 3339-3350 ◽  
Author(s):  
Avraham M. Libster ◽  
Ben Title ◽  
Yosef Yarom
Keyword(s):  
Firing Rate ◽  
Stress Responses ◽  
Sodium Current ◽  
Ionic Currents ◽  
Corticotropin Releasing Factor ◽  
Voltage Dependent ◽  
Biophysical Mechanism ◽  
The Central Nervous System ◽  
Firing Properties

Corticotropin-releasing factor (CRF) is a neuromodulator closely associated with stress responses. It is synthesized and released in the central nervous system by various neurons, including neurons of the inferior olive. The targets of inferior olivary neurons, the cerebellar Purkinje neurons (PNs), are endowed with CRF receptors. CRF increases the excitability of PNs in vivo, but the biophysical mechanism is not clear. Here we examine the effect of CRF on the firing properties of PNs using acute rat cerebellar slices. CRF increased the PN firing rate, regardless of whether they were firing tonically or switching between firing and quiescent periods. Current- and voltage-clamp experiments showed that the increase in firing rate was associated with a voltage shift of the activation curve of the persistent sodium current and hyperpolarizing-activated current, as well as activation of voltage-dependent potassium current. The multiple effects on various ionic currents, which are in agreement with the possibility that activation of CRF receptors triggers several intracellular pathways, are manifested as an increase excitability of PN.

Ultrastructural Correlations between Clonal Human Tumor Colonies and in Vivo Neoplasms

1982 ◽  
Vol 40 ◽  
pp. 210-211
Author(s):  
M.J. Murphy ◽  
R.R. Price ◽  
J.C. Sloman
Keyword(s):  
Cultured Cells ◽  
Human Tumor ◽  
Cell Type ◽  
Tumor Mass ◽  
Initial Cell ◽  
Cloning Assay ◽  
Human Tumor Cloning ◽  
The Relationship

The in vitro human tumor cloning assay originally described by Salmon and Hamburger has been applied recently to the investigation of differential anti-tumor drug sensitivities over a broad range of human neoplasms. A major problem in the acceptance of this technique has been the question of the relationship between the cultured cells and the original patient tumor, i.e., whether the colonies that develop derive from the neoplasm or from some other cell type within the initial cell population. A study of the ultrastructural morphology of the cultured cells vs. patient tumor has therefore been undertaken to resolve this question. Direct correlation was assured by division of a common tumor mass at surgical resection, one biopsy being fixed for TEM studies, the second being rapidly transported to the laboratory for culture.

The Infection of Cells by Bullet-Shaped Viruses

1969 ◽  
Vol 27 ◽  
pp. 372-373
Author(s):  
Frederick A. Murphy ◽  
Alyne K. Harrison ◽  
Sylvia G. Whitfield
Keyword(s):  
Electron Microscopy ◽  
Physical Properties ◽  
Host Cell ◽  
Thin Section ◽  
Cultured Cells ◽  
Cell Infection ◽  
Thin Section Electron Microscopy ◽  
Section Electron ◽  
Section Electron Microscopy

The bullet-shaped viruses are currently classified together on the basis of similarities in virion morphology and physical properties. Biologically and ecologically the member viruses are extremely diverse. In searching for further bases for making comparisons of these agents, the nature of host cell infection, both in vivo and in cultured cells, has been explored by thin-section electron microscopy.

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