scholarly journals Genetic expression of 4E-BP1 in juvenile mice alleviates mTOR-induced neuronal dysfunction and epilepsy

2021 ◽  
Author(s):  
Lena H Nguyen ◽  
Youfen Xu ◽  
Travorn Mahadeo ◽  
Longbo Zhang ◽  
Tiffany V Lin ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Firing Pattern ◽  
Intractable Epilepsy ◽  
Structure And Function ◽  
Resting Membrane Potential ◽  
Neuronal Dysfunction ◽  
Translational Repressor ◽  
Malformation Of Cortical Development ◽  
Channel Expression ◽  
And Function

Hyperactivation of mTOR signaling during fetal neurodevelopment alters neuron structure and function, leading to focal malformation of cortical development (FMCD) and intractable epilepsy. Recent evidence suggests increased cap-dependent translation downstream of mTOR contributes to FMCD formation and seizures. However, whether reducing overactive translation once the developmental pathologies are established reverses neuronal abnormalities and seizures is unknown. Here, we found that the translational repressor 4E-BP1, which is inactivated by mTOR-mediated phosphorylation, is hyperphosphorylated in patient FMCD tissue and in a mouse model of FMCD. Expressing constitutive active 4E-BP1 to repress aberrant translation in juvenile mice with FMCD reduced neuronal cytomegaly and corrected several electrophysiological alterations, including depolarized resting membrane potential, irregular firing pattern, and aberrant HCN4 channel expression. This was accompanied by improved cortical spectral activity and decreased seizures. Although mTOR controls multiple pathways, our study shows that targeting 4E-BP1-mediated translation alone is sufficient to alleviate neuronal dysfunction and ongoing epilepsy.

scholarly journals Decreased neuronal excitability in hippocampal neurons of mice exposed to cyclic hypoxia

2001 ◽  
Vol 91 (3) ◽  
pp. 1245-1250 ◽  
Author(s):  
Xiang Q. Gu ◽  
Gabriel G. Haddad
Keyword(s):  
Membrane Potential ◽  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Resting Membrane Potential ◽  
Ca1 Neurons ◽  
Recovery From Inactivation ◽  
Channel Expression ◽  
Steady State Inactivation ◽  
And Function

To study the physiological effects of chronic intermittent hypoxia on neuronal excitability and function in mice, we exposed animals to cyclic hypoxia for 8 h daily (12 cycles/h) for ∼4 wk, starting at 2–3 days of age, and examined the properties of freshly dissociated hippocampal neurons in vitro. Compared with control (Con) hippocampal CA1 neurons, exposed (Cyc) neurons showed action potentials (AP) with a smaller amplitude and a longer duration and a more depolarized resting membrane potential. They also have a lower rate of spontaneous firing of AP and a higher rheobase. Furthermore, there was downregulation of the Na+ current density in Cyc compared with Con neurons (356.09 ± 54.03 pA/pF in Cyc neurons vs. 508.48 ± 67.30 pA/pF in Con, P < 0.04). Na+ channel characteristics, including activation, steady-state inactivation, and recovery from inactivation, were similar in both groups. The deactivation rate, however, was much larger in Cyc than in Con (at −100 mV, time constant for deactivation = 0.37 ± 0.04 ms in Cyc neurons and 0.18 ± 0.01 ms in Con neurons). We conclude that the decreased neuronal excitability in mice neurons treated with cyclic hypoxia is due, at least in part, to differences in passive properties (e.g., resting membrane potential) and in Na+ channel expression and/or regulation. We hypothesize that this decreased excitability is an adaptive response that attempts to decrease the energy expenditure that is used for adjusting disturbances in ionic homeostasis in low-O2conditions.

Physiological role of Ca(2+)-activated and voltage-dependent K+ currents in rabbit coronary myocytes

1994 ◽  
Vol 266 (6) ◽  
pp. C1523-C1537 ◽  
Author(s):  
N. Leblanc ◽  
X. Wan ◽  
P. M. Leung
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Physiological Role ◽  
Cell Voltage ◽  
Resting Membrane Potential ◽  
Physiological Level ◽  
Steady State Current ◽  
Voltage Dependent ◽  
A Minor ◽  
And Function

The properties and function of Ca(2+)-activated K+ (KCa) and voltage-dependent K+ (IK) currents of rabbit coronary myocytes were studied under whole cell voltage-clamp conditions (22 degrees C). Inhibition of KCa by tetraethylammonium chloride (1-10 mM) or charybdotoxin (50-100 nM) suppressed noisy outward rectifying current elicited by 5-s voltage steps or ramp at potentials > 0 mV, reduced the hump of the biphasic ramp current-voltage relation, and shifted by less than +5 mV the potential at which no net steady-state current is recorded (Enet; index of resting membrane potential). Inhibition of steady-state inward Ca2+ currents [ICa(L)] by nifedipine (1 microM) displaced Enet by -11 mV. Analysis of steady-state voltage dependence of IK supported the existence of a "window" current between -50 and 0 mV. 4-Aminopyridine (2 mM) blocked a noninactivating component of IK evoked between -30 and -40 mV, abolished the hump current during ramps, and shifted Enet by more than +15 mV; hump current persisted during 2-min ramp depolarizations and peaked near the maximum overlap of the steady-state activation and inactivation curves of IK (about -22 mV). A threefold rise in extracellular Ca2+ concentration (1.8-5.4 mM) enhanced time-dependent outward K+ current (6.7-fold at +40 mV) and shifted Enet by -30 mV. It is concluded that, under steady-state conditions, IK and ICa(L) play a major role in regulating resting membrane potential at a physiological level of intracellular Ca2+ concentration, with a minor contribution from KCa. However, elevation of intracellular Ca2+ concentration enhances KCa and hyperpolarizes the myocyte to limit Ca2+ entry through ICa(L).

Chronic High-Inspired CO2 Decreases Excitability of Mouse Hippocampal Neurons

2007 ◽  
Vol 97 (2) ◽  
pp. 1833-1838 ◽  
Author(s):  
Xiang Q. Gu ◽  
Amjad Kanaan ◽  
Hang Yao ◽  
Gabriel G. Haddad
Keyword(s):  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Input Resistance ◽  
Resting Membrane Potential ◽  
Channel Current ◽  
Conductance Curve ◽  
Recovery From Inactivation ◽  
Channel Expression ◽  
Steady State Inactivation ◽  
And Function

To examine the effect of chronically elevated CO2 on excitability and function of neurons, we exposed mice to 8 and 12% CO2 for 4 wk (starting at 2 days of age), and examined the properties of freshly dissociated hippocampal neurons obtained from slices. Chronic CO2-treated neurons (CC) had a similar input resistance ( Rm) and resting membrane potential ( Vm) as control (CON). Although treatment with 8% CO2 did not change the rheobase (64 ± 11 pA, n = 9 vs. 47 ± 12 pA, n = 8 for CC 8% vs. CON; means ± SE), 12% CO2 treatment increased it significantly (73 ± 8 pA, n = 9, P = 0.05). Furthermore, the 12% CO2 but not the 8% CO2 treatment decreased the Na+ channel current density (244 ± 36 pA/pF, n = 17, vs. 436 ± 56 pA/pF, n = 18, for CC vs. CON, P = 0.005). Recovery from inactivation was also lowered by 12% but not 8% CO2. Other gating properties of Na+ current, such as voltage-conductance curve, steady-state inactivation, and time constant for deactivation, were not modified by either treatment. Western blot analysis showed that the expression of Na+ channel types I–III was not changed by 8% CO2 treatment, but their expression was significantly decreased by 20–30% ( P = 0.03) by the 12% treatment. We conclude from these data and others that neuronal excitability and Na+ channel expression depend on the duration and level of CO2 exposure and maturational changes occur in early life regarding neuronal responsiveness to CO2.

scholarly journals Renovascular disease induces mitochondrial damage in swine scattered tubular cells

2019 ◽  
Vol 317 (5) ◽  
pp. F1142-F1153 ◽  
Author(s):  
Arash Aghajani Nargesi ◽  
Xiang-Yang Zhu ◽  
Sabena M. Conley ◽  
John R. Woollard ◽  
Ishran M. Saadiq ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Structure And Function ◽  
Protective Effects ◽  
Renovascular Disease ◽  
Atp Production ◽  
Tubular Cells ◽  
Renal Tubular Cells ◽  
Mitochondrial Structure ◽  
And Function

Scattered tubular-like cells (STCs) contribute to repair neighboring injured renal tubular cells. Mitochondria mediate STC biology and function but might be injured by the ambient milieu. We hypothesized that the microenviroment induced by the ischemic and metabolic components of renovascular disease impairs STC mitochondrial structure and function in swine, which can be attenuated with mitoprotection. CD24+/CD133+ STCs were quantified in pig kidneys after 16 wk of metabolic syndrome (MetS) or lean diet (Lean) with or without concurrent renal artery stenosis (RAS) ( n = 6 each). Pig STCs were isolated and characterized, and mitochondrial structure, membrane potential, and oxidative stress were assessed in cells untreated or incubated with the mitoprotective drug elamipretide (1 nM for 6 h). STC-protective effects were assessed in vitro by their capacity to proliferate and improve viability of injured pig tubular epithelial cells. The percentage of STCs was higher in MetS, Lean + RAS, and MetS + RAS kidneys compared with Lean kidneys. STCs isolated from Lean + RAS and MetS + RAS pigs showed mitochondrial swelling and decreased matrix density, which were both restored by mitoprotection. In addition, mitochondrial membrane potential and ATP production were reduced and production of reactive oxygen species elevated in MetS, Lean + RAS, and MetS + RAS STCs. Importantly, mitoprotection improved mitochondrial structure and function as well as the capacity of MetS + RAS STCs to repair injured tubular cells in vitro. Renovascular disease in swine is associated with a higher prevalence of STCs but induces structural and functional alterations in STC mitochondria, which impair their reparative potency. These observations suggest a key role for mitochondria in the renal reparative capacity of STCs.

Influence of cloned voltage-gated K+ channel expression on alanine transport, Rb+ uptake, and cell volume

1993 ◽  
Vol 265 (5) ◽  
pp. C1230-C1238 ◽  
Author(s):  
A. Felipe ◽  
D. J. Snyders ◽  
K. K. Deal ◽  
M. M. Tamkun
Keyword(s):  
Membrane Potential ◽  
Atpase Activity ◽  
Cell Volume ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Wild Type ◽  
Transfected Cells ◽  
Voltage Gated ◽  
Alanine Transport ◽  
Channel Expression

Voltage-gated K+ channels are involved in regulation of action potential duration and in setting the resting membrane potential in nerve and muscle. To determine the effects of voltage-gated K+ channel expression on processes not associated with electrically excitable cells, we studied cell volume, membrane potential, Na(+)-K(+)-ATPase activity, and alanine transport after the stable expression of the Kv1.4 and Kv1.5 human K+ channels in Ltk- mouse fibroblasts (L-cells). The fast-activating noninactivating Kv1.5 channel, but not the rapidly inactivating Kv1.4 channel, prevented dexamethasone-induced increases in intracellular volume and inhibited Na(+)-K(+)-ATPase activity by 25%, as measured by 86Rb+ uptake. Alanine transport, measured separately by systems A and ASC, was lower in Kv1.5-expressing cells, indicating that the expression of this channel modified the Na(+)-dependent amino acid transport of both systems. Expression of the Kv1.4 channel did not alter alanine transport relative to wild-type or sham-transfected cells. The changes specific to Kv1.5 expression may be related to the resting membrane potential induced by this channel (-30 mV) in contrast to that measured in wild-type sham-transfected, or Kv1.4-transfected cells (-2 to 0 mV). Blocking of the Kv1.5 channel by 60 microM quinidine negated the effects of Kv1.5 expression on intracellular volume, Na(+)-K(+)-ATPase, and Na(+)-dependent alanine transport. These results indicate that delayed rectifier channels such as Kv1.5 can play a key role in the control of cell membrane potential, cell volume, Na(+)-K(+)-ATPase activity, and electrogenic alanine transport across the plasma membrane of electrically unexcitable cells.

Structure and function of neural networks in the retina

1988 ◽  
Vol 46 ◽  
pp. 26-27
Author(s):  
Peter Sterling
Keyword(s):  
Ganglion Cells ◽  
Three Dimensional ◽  
Structure And Function ◽  
Synaptic Connections ◽  
Visual Axis ◽  
One Dimensional ◽  
Cat Retina ◽  
Ultrathin Sections ◽  
And Function ◽  
Insight Into

The synaptic connections in cat retina that link photoreceptors to ganglion cells have been analyzed quantitatively. Our approach has been to prepare serial, ultrathin sections and photograph en montage at low magnification (˜2000X) in the electron microscope. Six series, 100-300 sections long, have been prepared over the last decade. They derive from different cats but always from the same region of retina, about one degree from the center of the visual axis. The material has been analyzed by reconstructing adjacent neurons in each array and then identifying systematically the synaptic connections between arrays. Most reconstructions were done manually by tracing the outlines of processes in successive sections onto acetate sheets aligned on a cartoonist's jig. The tracings were then digitized, stacked by computer, and printed with the hidden lines removed. The results have provided rather than the usual one-dimensional account of pathways, a three-dimensional account of circuits. From this has emerged insight into the functional architecture.

Osseointegration interface of calcified bone and endosseous implants

1992 ◽  
Vol 50 (2) ◽  
pp. 1096-1097
Author(s):  
K.E. Krizan ◽  
J.E. Laffoon ◽  
M.J. Buckley
Keyword(s):  
Structure And Function ◽  
Titanium Implants ◽  
En Bloc ◽  
Endosseous Implants ◽  
Ultrastructural Studies ◽  
The Past ◽  
Cacodylate Buffer ◽  
One Year ◽  
And Function

With increase use of tissue-integrated prostheses in recent years it is a goal to understand what is happening at the interface between haversion bone and bulk metal. This study uses electron microscopy (EM) techniques to establish parameters for osseointegration (structure and function between bone and nonload-carrying implants) in an animal model. In the past the interface has been evaluated extensively with light microscopy methods. Today researchers are using the EM for ultrastructural studies of the bone tissue and implant responses to an in vivo environment. Under general anesthesia nine adult mongrel dogs received three Brånemark (Nobelpharma) 3.75 × 7 mm titanium implants surgical placed in their left zygomatic arch. After a one year healing period the animals were injected with a routine bone marker (oxytetracycline), euthanized and perfused via aortic cannulation with 3% glutaraldehyde in 0.1M cacodylate buffer pH 7.2. Implants were retrieved en bloc, harvest radiographs made (Fig. 1), and routinely embedded in plastic. Tissue and implants were cut into 300 micron thick wafers, longitudinally to the implant with an Isomet saw and diamond wafering blade [Beuhler] until the center of the implant was reached.

Use of human autoantibodies and immunoelectron microscopy to study structure and function of the nucleolus and nuclear bodies

1992 ◽  
Vol 50 (1) ◽  
pp. 506-507
Author(s):  
Robert L. Ochs
Keyword(s):  
Electron Microscopy ◽  
Structure And Function ◽  
Nuclear Bodies ◽  
Nuclear Interior ◽  
Coiled Bodies ◽  
Interchromatin Granules ◽  
And Function ◽  
Conventional Electron Microscopy ◽  
Perichromatin Granules ◽  
Perichromatin Fibrils

By conventional electron microscopy, the formed elements of the nuclear interior include the nucleolus, chromatin, interchromatin granules, perichromatin granules, perichromatin fibrils, and various types of nuclear bodies (Figs. 1a-c). Of these structures, all have been reasonably well characterized structurally and functionally except for nuclear bodies. The most common types of nuclear bodies are simple nuclear bodies and coiled bodies (Figs. 1a,c). Since nuclear bodies are small in size (0.2-1.0 μm in diameter) and infrequent in number, they are often overlooked or simply not observed in any random thin section. The rat liver hepatocyte in Fig. 1b is a case in point. Historically, nuclear bodies are more prominent in hyperactive cells, they often occur in proximity to nucleoli (Fig. 1c), and sometimes they are observed to “bud off” from the nucleolar surface.

Depletion and Reconstitution of Active E. Coli Ribosomes

1975 ◽  
Vol 33 ◽  
pp. 640-641
Author(s):  
M. Boublik ◽  
W. Hellmann ◽  
F. Jenkins
Keyword(s):  
Protein Biosynthesis ◽  
Large Subunit ◽  
High Resolution Electron Microscopy ◽  
Small Subunit ◽  
Structure And Function ◽  
Biologically Active ◽  
Biological Macromolecules ◽  
E Coli ◽  
Resolution Electron ◽  
And Function

Correlations between structure and function of biological macromolecules have been studied intensively for many years, mostly by indirect methods. High resolution electron microscopy is a unique tool which can provide such information directly by comparing the conformation of biopolymers in their biologically active and inactive state. We have correlated the structure and function of ribosomes, ribonucleoprotein particles which are the site of protein biosynthesis. 70S E. coli ribosomes, used in this experiment, are composed of two subunits - large (50S) and small (30S). The large subunit consists of 34 proteins and two different ribonucleic acid molecules. The small subunit contains 21 proteins and one RNA molecule. All proteins (with the exception of L7 and L12) are present in one copy per ribosome.This study deals with the changes in the fine structure of E. coli ribosomes depleted of proteins L7 and L12. These proteins are unique in many aspects.

The Laryngeal Epithelium in Reflux

2011 ◽  
Vol 21 (3) ◽  
pp. 112-117 ◽  
Author(s):  
Elizabeth Erickson-Levendoski ◽  
Mahalakshmi Sivasankar
Keyword(s):  
Laryngopharyngeal Reflux ◽  
Critical Role ◽  
Structure And Function ◽  
Laryngeal Disease ◽  
Health And Disease ◽  
And Function ◽  
The Impact

The epithelium plays a critical role in the maintenance of laryngeal health. This is evident in that laryngeal disease may result when the integrity of the epithelium is compromised by insults such as laryngopharyngeal reflux. In this article, we will review the structure and function of the laryngeal epithelium and summarize the impact of laryngopharyngeal reflux on the epithelium. Research investigating the ramifications of reflux on the epithelium has improved our understanding of laryngeal disease associated with laryngopharyngeal reflux. It further highlights the need for continued research on the laryngeal epithelium in health and disease.

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