Absence Of Electrical Stimulation Research Articles

Regulation of cardiomyocyte t-tubule structure by preload and afterload: Roles in cardiac compensation and decompensation.

Mechanical load is a potent regulator of cardiac structure and function. Although high workload during heart failure is associated with disruption of cardiomyocyte t-tubules and Ca2+ homeostasis, it remains unclear whether changes in preload and afterload may promote adaptive t-tubule remodelling. We examined this issue by first investigating isolated effects of stepwise increases in load in cultured rat papillary muscles. Both preload and afterload increases produced a biphasic response, with the highest t-tubule densities observed at moderate loads, whereas excessively low and high loads resulted in low t-tubule levels. To determine the baseline position of the heart on this bell-shaped curve, mice were subjected to mildly elevated preload or afterload (1week of aortic shunt or banding). Both interventions resulted in compensated cardiac function linked to increased t-tubule density, consistent with ascension up the rising limb of the curve. Similar t-tubule proliferation was observed in human patients with moderately increased preload or afterload (mitral valve regurgitation, aortic stenosis). T-tubule growth was associated with larger Ca2+ transients, linked to upregulation of L-type Ca2+ channels, Na+-Ca2+ exchanger, mechanosensors and regulators of t-tubule structure. By contrast, marked elevation of cardiac load in rodents and patients advanced the heart down the declining limb of the t-tubule-load relationship. This bell-shaped relationship was lost in the absence of electrical stimulation, indicating a key role of systolic stress in controlling t-tubule plasticity. In conclusion, modest augmentation of workload promotes compensatory increases in t-tubule density and Ca2+ cycling, whereas this adaptation is reversed in overloaded hearts during heart failure progression. KEY POINTS: Excised papillary muscle experiments demonstrated a bell-shaped relationship between cardiomyocyte t-tubule density and workload (preload or afterload), which was only present when muscles were electrically stimulated. The in vivo heart at baseline is positioned on the rising phase of this curve because moderate increases in preload (mice with brief aortic shunt surgery, patients with mitral valve regurgitation) resulted in t-tubule growth. Moderate increases in afterload (mice and patients with mild aortic banding/stenosis) similarly increased t-tubule density. T-tubule proliferation was associated with larger Ca2+ transients, with upregulation of the L-type Ca2+ channel, Na+-Ca2+ exchanger, mechanosensors and regulators of t-tubule structure. By contrast, marked elevation of cardiac load in rodents and patients placed the heart on the declining phase of the t-tubule-load relationship, promoting heart failure progression. The dependence of t-tubule structure on preload and afterload thus enables both compensatory and maladaptive remodelling, in rodents and humans.

Omecamtiv mecarbil augments cardiomyocyte contractile activity both at resting and systolic Ca2+ levels.

Heart failure with reduced ejection fraction (HFrEF) is a disease with high mortality and morbidity. Recent positive inotropic drug developments focused on cardiac myofilaments, that is, direct activators of the myosin molecule and Ca2+ sensitizers for patients with advanced HFrEF. Omecamtiv mecarbil (OM) is the first direct myosin activator with promising results in clinical studies. Here, we aimed to elucidate the cellular mechanisms of the positive inotropic effect of OM in a comparative in vitro investigation where Ca2+ -sensitizing positive inotropic agents with distinct mechanisms of action [EMD 53998 (EMD), which also docks on the myosin molecule, and levosimendan (Levo), which binds to troponin C] were included. Enzymatically isolated canine cardiomyocytes with intact cell membranes were loaded with Fura-2AM, a Ca2+ -sensitive, ratiometric, fluorescent dye. Changes in sarcomere length (SL) and intracellular Ca2+ concentration were recorded in parallel at room temperature, whereas cardiomyocyte contractions were evoked by field stimulation at 0.1Hz in the presence of different OM, EMD, or Levo concentrations. SL was reduced by about 23% or 9% in the presence of 1μM OM or 1μM EMD in the absence of electrical stimulation, whereas 1μM Levo had no effect on resting SL. Fractional sarcomere shortening was increased by 1μM EMD or 1μM Levo to about 152%, but only to about 128% in the presence of 0.03μM OM. At higher OM concentrations, no significant increase in fractional sarcomere shortening could be recorded. Contraction durations largely increased, whereas the kinetics of contractions and relaxations decreased with increasing OM concentrations. One-micromole EMD or 1μM Levo had no effects on contraction durations. One-micromole Levo, but not 1μM EMD, accelerated the kinetics of cardiomyocyte contractions and relaxations. Ca2+ transient amplitudes were unaffected by all treatments. Our data revealed major distinctions between the cellular effects of myofilament targeted agents (OM, EMD, or Levo) depending on their target proteins and binding sites, although they were compatible with the involvement of Ca2+ -sensitizing mechanisms for all three drugs. Significant part of the cardiotonic effect of OM relates to the prolongation of systolic contraction in combination with its Ca2+ -sensitizing effect.

Impact Of Tdcs On Esports Performance

PURPOSE: The purpose of this study was to examine the impact of transcranial direct current stimulation (tDCS) on esport performance. A secondary aim was to determine the physiological responses to chronic tDCS before esport training sessions. The authors hypothesized that the esports group would show greater improvements in performance during the 10 esports training sessions when compared to the sham group. METHODS: A total of 23 male college students (22 ± 2.4 years; 26.8 ± 4.5 kg/m2; 5.6 ± 3.8 hours of exercise per week; 10.8 ± 5.9 hours of esports per week) were recruited to participate in this double-blind randomized-controlled trial. Eligibility was limited to healthy individuals between the ages of 18 to 35 who currently play at least 6 hours of esports per week. Recently a commercially available tDCS headset (Halo Sport; Halo Neuroscience, San Francisco, CA) has been developed to apply tDCS in a practical setting. In a double-blind fashion, participants were placed into the experimental (HALO) and control (SHAM) groups for 10 visits. On the HALO group (n = 12), a 20-minute tDCS was performed prior to the esports training on trials 2-9. No stimulation was performed on the first and last esports training sessions on both groups. The same Halo Sport tDCS devices were utilized with the SHAM group (n = 11), however, with the absence of electrical stimulation. Regardless of group placement, every participant engaged in the same 30-minute esports session utilizing Aim Hero during the 10 visits. Two-Way Repeated Measures ANOVA were utilized to examine whether there were differences between and within groups across all 10 visits. Statistical analysis was performed using SPSS (v.27) and alpha was set at 0.05. RESULTS: When considering the accuracy of the players during the esports session, there were no statistically significantly differences for the main effect of group (p = 0.69). The main effect of time was statistically significant (p < 0.01), suggesting an increase in esports performance during the 10 visits. CONCLUSIONS: Participants utilizing Halo Sport’s tDCS did not improve esports performance following eight stimulation training sessions when compared to SHAM group. Further research is warranted to examine if tDCS can aid gamers to avoid fatigue during long esports sessions.

Genome association of carcass and palatability traits from Bos indicus-Bos taurus crossbred steers within electrical stimulation status and correspondence with steer temperament 2. Palatability

Genome wide association analyses were conducted for palatability traits in the presence or absence of electrical stimulation. Palatability traits were measured on steaks from Nellore-Angus steers (n = 350). No palatability traits were correlated (|r| < 0.18) with steer temperament. Nine SNP on BTA 29 from 35.7 Mb to 48.2 Mb were associated with muscle fiber or overall tenderness, and/or connective tissue amount measured on steaks from carcass sides not electrically stimulated. Only three of these SNP were associated with these traits on the electrically stimulated carcass side. Associated SNP with connective tissue amount were only detected in steaks from carcass sides not subjected to electrical stimulation. Sixteen other BTA 29 SNP were associated with at least one tenderness trait from the electrically stimulated carcass side. One SNP on BTA 4 and 24 were associated with juiciness and overall tenderness, respectively. Candidate genes on BTA 29 included EGF containing fibulin extracellular matrix protein 2 (EFEMP), slingshot protein phosphatase 3 (SSH3), achaete-scute family bHLH transcription factor 2 (ASCL2). Although not detected as a candidate gene, the associated SNP with the various tenderness traits on BTA 29 may indicate the importance of calpain 1 (CAPN1), which has been considered influential on beef tenderness.

A Novel Conductive and Micropatterned PEG-Based Hydrogel Enabling the Topographical and Electrical Stimulation of Myoblasts.

In this study, we designed a cell-adhesive poly(ethylene glycol) (PEG)-based hydrogel that simultaneously provides topographical and electrical stimuli to C2C12 myoblasts. Specifically, PEG hydrogels with microgroove structures of 3 μm ridges and 3 μm grooves were prepared by micromolding; in situ polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) was then performed within the micropatterned PEG hydrogels to create a microgrooved conductive hydrogel (CH/P). The CH/P had clear replica patterns of the silicone mold and a conductivity of 2.49 × 10-3 S/cm, with greater than 85% water content. In addition, the CH exhibited Young's modulus (45.84 ± 7.12kPa) similar to that of a muscle tissue. The surface of the CH/P was further modified via covalent bonding with cell-adhesive peptides to facilitate cell adhesion without affecting conductivity. An in vitro cell assay revealed that the CH/P was cytocompatible and enhanced the cell alignment and elongation of C2C12 myoblasts. The microgrooves and conductivity of the CH/P had the greatest positive effect on the myogenesis of C2C12 myoblasts compared to the other PEG hydrogel samples without conductivity or/and microgrooves, even in the absence of electrical stimulation. Electrical stimulation studies indicated that the combination of topographical and electrical cues maximized the differentiation of C2C12 myoblasts into myotubes, confirming the synergetic effect of incorporating microgroove surface features and a conductive PEDOT component into hydrogels.

Fabrication of electroactive polypyrrole-tungsten disulfide nanocomposite for enhanced in vivo drug release in mice skin

The present study focused on the development of electric stimuli drug release carrier based on transition metal dicgalcogenides. First, tungsten disulfide (WS2) was exfoliated and functionalized using thiol chemistry with various thiol-terminated ligands such as thioglycolic acid (TGA), mercaptosuccinic acid (MSA), and 2-ethanethiol (2ET). The exfoliated WS2 underwent non-covalent coating with an electrically conductive polypyrrole (PPy) for functionalization, of which MSA-WS2-PPy achieved the highest 5-FU (anticancer drug) loading. An electrically-stimulated drug release experiment showed that TGA-WS2-PPy achieved a higher drug release (90%) than MSA-WS2-PPy (70%) and 2ET-WS2-Ppy (35%). The TGA-WS2-PPy exhibited swelling/recombination between PPY and MSA-WS2 substrate under electrical stimulation, resulting in the highest 5-FU release. From the MTT assay result, there was no significant toxicity observed for TGA-WS2-PPy-FU on HaCaT cells, indicating the biocompatibility of TGA-WS2-PPy-FU in the absence of electrical stimulation. However, HaCaT cells died when incubated with TGA-WS2-PPy-FU under electrical stimulation. Finally, Raman mapping studies for TGA-WS2-PPy drug release in the skin of nude mice demonstrated that the carrier penetrated deeper into the skin of the mice while other systems failed to exhibit significant effects under electrical stimulation. The present study offers a novel approach in developing a non-invasive electrically-stimulated drug release system based on WS2 and an externally-controlled delivery model.

Graphene Sheet-Induced Global Maturation of Cardiomyocytes Derived from Human Induced Pluripotent Stem Cells.

Human induced pluripotent stem cells (hiPSCs) can proliferate infinitely. Their ability to differentiate into cardiomyocytes provides abundant sources for disease modeling, drug screening and regenerative medicine. However, hiPSC-derived cardiomyocytes (hiPSC-CMs) display a low degree of maturation and fetal-like properties. Current in vitro differentiation methods do not mimic the structural, mechanical, or physiological properties of the cardiogenesis niche. Recently, we present an efficient cardiac maturation platform that combines hiPSCs monolayer cardiac differentiation with graphene substrate, which is a biocompatible and superconductive material. The hiPSCs lines were successfully maintained on the graphene sheets and were able to differentiate into functional cardiomyocytes. This strategy markedly increased the myofibril ultrastructural organization, elevated the conduction velocity, and enhanced both the Ca2+ handling and electrophysiological properties in the absence of electrical stimulation. On the graphene substrate, the expression of connexin 43 increased along with the conduction velocity. Interestingly, the bone morphogenetic proteins signaling was also significantly activated during early cardiogenesis, confirmed by RNA sequencing analysis. Here, we reasoned that graphene substrate as a conductive biomimetic surface could facilitate the intrinsic electrical propagation, mimicking the microenvironment of the native heart, to further promote the global maturation of hiPSC-CMs. Our findings highlight the capability of electrically active substrates to influence cardiomyocyte development. We believe that application of graphene sheets will be useful for simple, fast, and scalable maturation of regenerated cardiomyocytes.

Synergistic effect of topography, surface chemistry and conductivity of the electrospun nanofibrous scaffold on cellular response of PC12 cells

Electrospun nanofibrous nerve implants is a promising therapy for peripheral nerve injury, and its performance can be tailored by chemical cues, topographical features as well as electrical properties. In this paper, a surface modified, electrically conductive, aligned nanofibrous scaffold composed of poly (lactic acid) (PLA) and polypyrrole (Ppy), referred to as o-PLAPpy_A, was fabricated for nerve regeneration. The morphology, surface chemistry and hydrophilicity of nanofibers were characterized by Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and water contact angle, respectively. The effects of these nanofibers on neuronal differentiation using PC12 cells were evaluated. A hydrophilic surface was created by Poly-ornithine coating, which was able to provide a better environment for cell attachment, and furthermore aligned fibers were proved to be able to guide PC12 cells grow along the fiber direction and be beneficial for neurite outgrowth. The cellular response of PC12 cells to pulsed electrical stimulation was evaluated by NF 200 and alpha tubulin expression, indicating that electrical stimulation with a voltage of 40mV could enhance the neurite outgrowth. The PC12 cells stimulated with electrical shock showed greater level of neurite outgrowth and smaller cell body size. Moreover, the PC12 cells under electrical stimulation showed better viability. In summary, the o-PLAPpy_A nanofibrous scaffold supported the attachment, proliferation and differentiation of PC12 cells in the absence of electrical stimulation, which could be potential candidate for nerve regeneration applications.

Telemetry changes over time in cochlear implant patients

Objectives: This is a cross-sectional study conducted on cochlear implant recipients, to monitor changes in recorded impedance telemetry and evoked compound action potentials (ECAP) measured during surgery versus the same measures at post implant follow-up visits. An additional aim was to correlate the recorded ECAP measures with the patient's post-operative performance and to evaluate the incidence of abnormal intra-operative cochlear implant telemetry measurements and their changes at device activation. Study design: The present study comprised 44 subjects – 12 adults and 32 children of both genders – implanted at the Cochlear Implant Unit, Cairo University. ECAP thresholds and electrode impedance measures were collected intra-operatively, at initial stimulation, and at 9–12 months post initial stimulation. Measurements were compared at the three intervals and ECAP measures were correlated to the patient's post-operative performance in the form of aided sound field thresholds, speech detection and discrimination for adults and language assessment for children. Results: In the absence of electrical stimulation, there was an increase of impedance on all electrodes at the initial stimulation visit, which decreased at the 9–12 months follow-up. Open circuit findings were more prevalent than short circuits. Children had higher impedance values at post implant activation compared to adult patients. No correlation existed between ECAP thresholds and post-operative patient performance at the one-year evaluation. Conclusion: At the time of surgery, telemetry provides valuable information regarding the electrical output of the implant and the response of the auditory system to electrical stimulation; however, it is not a valuable predictor of post-operative performance.

Exocytosis of serotonin from the neuronal soma is sustained by a serotonin and calcium-dependent feedback loop.

The soma of many neurons releases large amounts of transmitter molecules through an exocytosis process that continues for hundreds of seconds after the end of the triggering stimulus. Transmitters released in this way modulate the activity of neurons, glia and blood vessels over vast volumes of the nervous system. Here we studied how somatic exocytosis is maintained for such long periods in the absence of electrical stimulation and transmembrane Ca2+ entry. Somatic exocytosis of serotonin from dense core vesicles could be triggered by a train of 10 action potentials at 20 Hz in Retzius neurons of the leech. However, the same number of action potentials produced at 1 Hz failed to evoke any exocytosis. The 20-Hz train evoked exocytosis through a sequence of intracellular Ca2+ transients, with each transient having a different origin, timing and intracellular distribution. Upon electrical stimulation, transmembrane Ca2+ entry through L-type channels activated Ca2+-induced Ca2+ release. A resulting fast Ca2+ transient evoked an early exocytosis of serotonin from sparse vesicles resting close to the plasma membrane. This Ca2+ transient also triggered the transport of distant clusters of vesicles toward the plasma membrane. Upon exocytosis, the released serotonin activated autoreceptors coupled to phospholipase C, which in turn produced an intracellular Ca2+ increase in the submembrane shell. This localized Ca2+ increase evoked new exocytosis as the vesicles in the clusters arrived gradually at the plasma membrane. In this way, the extracellular serotonin elevated the intracellular Ca2+ and this Ca2+ evoked more exocytosis. The resulting positive feedback loop maintained exocytosis for the following hundreds of seconds until the last vesicles in the clusters fused. Since somatic exocytosis displays similar kinetics in neurons releasing different types of transmitters, the data presented here contributes to understand the cellular basis of paracrine neurotransmission.

Neurite outgrowth on electrospun PLLA fibers is enhanced by exogenous electrical stimulation

Objective. Both electrical stimuli (endogenous and exogenous) and topographical cues are instructive to axonal extension. This report, for the first time, investigated the relative dominance of directional topographical guidance cues and directional electrical cues to enhance and/or direct primary neurite extension. We hypothesized the combination of electrical stimulation with electrospun fiber topography would induce longer neurite extension from dorsal root ganglia neurons than the presence of electrical stimulation or aligned topography alone. Approach. To test the hypothesis, neurite outgrowth was examined on laminin-coated poly-L-lactide films or electrospun fibers (2 µm in diameter) in the presence or absence of electrical stimulation. Immunostained neurons were semi-automatically traced using Neurolucida software and morphology was evaluated. Main Results. Neurite extension increased 74% on the aligned fibers compared to film controls. Stimulation alone increased outgrowth by 32% on films or fibers relative to unstimulated film controls. The co-presentation of topographical (fibers) with biophysical (electrical stimulation) cues resulted in a synergistic 126% increase in outgrowth relative to unstimulated film controls. Field polarity had no influence on the directionality of neurites, indicating topographical cues are responsible for guiding neurite extension. Significance. Both cues (electrical stimulation and fiber geometry) are modular in nature and can be synergistically applied in conjunction with other common methods in regenerative medicine such as controlled release of growth factors to further influence axonal growth in vivo. The combined application of electrical and aligned fiber topographical guidance cues described herein, if translated in vivo, could provide a more supportive environment for directed and robust axonal regeneration following peripheral nerve injury.

Doxorubicin Stimulates the Na+/Ca2+ Exchanger in Ventricular Cardiomyocytes

Doxorubicin (DOX) is a widely used antineoplastic agent that exerts cardiotoxic effects. This study analyzed the effects of a clinically relevant DOX concentration (30 μM) on Ca2+ transport in rat ventricular myocytes. DOX decreased the sarcoplasmic reticulum (SR) Ca2+ content ([Ca2+]SR) (15%, p<0.001), however without significant change in Ca2+ transient amplitude and kinetics, or in the fraction of [Ca2+]SR released at a twitch. DOX abbreviated [Ca2+]i decline of caffeine-evoked transients (p<0.001). Estimates of the integrated Ca2+ fluxes attributable to individual transporters during twitch [Ca2+]i decline indicated a small depression of SR Ca2+ uptake (12%, p<0.05), but great enhancement of Ca2+ efflux via the Na+/Ca2+ exchanger (NCX) (90%, p<0.05), so that the contribution of the latter to cytosolic Ca2+ removal more than doubled. To promote NCX-mediated Ca2+ influx in the absence of electrical stimulation, extracellular [Na+] was lowered from 140 to 105 mM. In these conditions, DOX exposure increased both the rate constant of [Ca2+]i rise (12.8±1.4 vs. 4.8±0.8 nM.s-1) and the rate of spontaneous Ca2+ transients (0.18±0.04 vs. 0.05±0.01 Hz, p<0.05). After SR function inhibition with thapsigargin, spontaneous Ca2+ transients were absent, but NCX-mediated increase in [Ca2+]i remained greater in the presence of DOX (190±35 vs. 74±18 nM.min-1, p<0.01), which was abolished by inhibition of reverse NCX with 10 μM KB-R7943 (−29±6 nM.min-1, p<0.01). The results indicate that DOX altered mainly diastolic Ca2+ handling, causing mild inhibition of SR Ca2+ uptake, but marked increase of Ca2+ transport via NCX. The latter effect does not seem to be due to thermodynamic factors, but probably to NCX stimulation, as both Ca2+ influx and efflux were enhanced.

Beyond the silence: Bilateral somatosensory stimulation enhances skilled movement quality and neural density in intact behaving rats

It is thought that a close dialogue between the primary motor (M1) and somatosensory (S1) cortices is necessary for skilled motor learning. The extent of the relative S1 contribution in producing skilled reaching movements, however, is still unclear. Here we used anodal transcranial direct current stimulation (tDCS), which is able to alter polarity-specific excitability in the S1, to facilitate skilled movement in intact behaving rats. We hypothesized that the critical role of S1 in reaching performance can be enhanced by bilateral tDCS. Pretrained rats were assigned to control or stimulation conditions: (1) UnAno: the unilateral application of an anodal current to the side contralateral to the paw preferred for reaching; (2) BiAno1: bilateral anodal current; (3) BiAno2: a bilateral anodal current with additional 30ms of 65μA pulses every 5s. Rats received tDCS (65μA; 10min/rat) to the S1 during skilled reach training for 20 days (online-effect phase). After-effect assessment occurred for the next ten days in the absence of electrical stimulation. Quantitative and qualitative analyses of online-effects of tDCS showed that UnAno and BiAno1 somatosensory stimulation significantly improve skilled reaching performance. Bilateral BiAno1 stimulation was associated with greater qualitative functional improvement than unilateral UnAno stimulation. tDCS-induced improvements were not observed in the after-effects phase. Quantitative cytoarchitectonic analysis revealed that somatosensory tDCS bilaterally increases cortical neural density. The findings emphasize the central role of bilateral somatosensory feedback in skill acquisition through modulation of cortico-motor excitability.

Atp-Induced Membrane Depolarization Relates to Skeletal Muscle Fibers Plasticity

In adult muscle fibers, 20 Hz electrical stimulation activates a signaling cascade that starts with Cav1.1 activation, ATP release trough pannexin channels, purinergic receptors activation and IP3-dependent calcium signals, to finally lead to gene transcription related to fast to slow muscle fiber type transition. ATP release plays a key role in this process, being able to activate, in the absence of electrical stimulation, most of the transcriptional changes observed after 20 Hz stimulation.We found that addition of 100-500 μM external ATP induced muscle fiber depolarization (reaching membrane potential values of −40 mV to −30 mV) and that transcriptional changes observed after stimulation of fibers with 30 μM external ATP, were abolished by 25 μM nifedipine, a Cav1.1 inhibitor. In fibers depolarized to similar membrane potential values with external K+, we documented calcium signals and transcriptional changes similar to those observed after 20 Hz stimulation. These two events were completely inhibited by the IP3R blocker Xestospongin B, suggesting that IP3-dependent events are triggered at these membrane depolarization values.These results suggest that ATP released by muscle fibers after 20 Hz stimulation may activate the signaling pathway leading to transcriptional changes by inducing small depolarization of muscle cell membrane. This may constitute either a primary or a reinforcement signal during the muscle plasticity process we described to occur after 20 Hz electrical stimulation.ACT1111, FONDECYT 1110467, FONDAP 15010006

FEF-microstimulation causes task-dependent modulation of occipital fMRI activity

Electrical microstimulation of FEF (FEF-EM) modulates neuronal activity in area V4 (Moore and Armstrong, 2003) and elicits functional magnetic resonance imaging (fMRI) activations in visual cortex in a bottom-up dependent manner (Ekstrom et al., 2008). Here we test the hypothesis that FEF-EM-induced modulations of fMRI activity are also function of task demands, which would suggest top-down dependent gating of FEF signals in early visual cortex. We scanned two monkeys performing a visually guided saccade task; a passive fixation task with a very similar visual display; and a passive fixation task without peripheral dots. We found increased effects of FEF-EM on fMRI-activity in visual cortex during saccades compared to fixation, indicating that the FEF-EM induced modulation is task-dependent. Finally, the effect of FEF-EM is mainly present in voxels which were less activated by visual stimuli in the absence of electrical stimulation. Our results show that the FEF-EM-induced pattern of activation in early visual cortex is topographically specific and more pronounced during increased task demands. These results fit with models suggesting that FEF is an important source modulating activity in early sensory cortex and that these influences can be enhanced by coincident bottom-up or top-down signals.

Effects of moderate electrical stimulation on reactive species production by primary rat skeletal muscle cells: Cross talk between superoxide and nitric oxide production

The effects of a moderate electrical stimulation on superoxide and nitric oxide production by primary cultured skeletal muscle cells were evaluated. The involvement of the main sites of these reactive species production and the relationship between superoxide and nitric oxide production were also examined. Production of superoxide was evaluated by cytochrome c reduction and dihydroethidium oxidation assays. Electrical stimulation increased superoxide production after 1 h incubation. A xanthine oxidase inhibitor caused a partial decrease of superoxide generation and a significant amount of mitochondria-derived superoxide was also observed. Nitric oxide production was assessed by nitrite measurement and by using 4,5-diaminofluorescein diacetate (DAF-2-DA) assay. Using both methods an increased production of nitric oxide was obtained after electrical stimulation, which was also able to induce an increase of iNOS content and NF-κB activation. The participation of superoxide in nitric oxide production was investigated by incubating cells with DAF-2-DA in the presence or absence of electrical stimulation, a superoxide generator system (xanthine-xanthine oxidase), a mixture of NOS inhibitors and SOD-PEG. Our data show that the induction of muscle contraction by a moderate electrical stimulation protocol led to an increased nitric oxide production that can be controlled by superoxide generation. The cross talk between these reactive species likely plays a role in exercise-induced maintenance and adaptation by regulating muscular glucose metabolism, force of contraction, fatigue, and antioxidant systems activities.

Well-Ordered Porous Conductive Polypyrrole as a New Platform for Neural Interfaces

We present the preparation of electrically conductive, porous polypyrrole surfaces and demonstrate their use as an interactive substrate for neuronal growth. Nerve growth factor (NGF)-loaded porous conducting polymers were initially prepared by electrochemical deposition of a mixture of pyrrole monomers and NGF into two- or three-dimensional particle arrays followed by subsequent removal of a sacrificial template. Morphological observation by scanning electron microscopy (SEM) revealed these to possess high regularity and porosity with well-defined topographical features. A four-point probe study demonstrated remarkable electrical activities despite the presence of voids. In addition, we investigated the effects of these surfaces on cellular behaviors using PC 12 cells in the presence and absence of electrical stimulation. Our results suggest that the surface topography as well as an applied electrical field can play a crucial role in determining further cell responses. Indeed, surface-induced preferential regulation leads to enhanced cellular viability and neurite extension. Establishing the underlying cellular mechanisms in response to various external stimuli is essential in that one can elicit positive neuronal guidance and modulate their activities by engineering a series of electrical, chemical, and topographical cues.

CAMKII Mediates Cardiac Glycoside Toxicity

The positive inotropic effect produced by inhibition of Na+/K+ ATPase (NKA) with digitalis has been used for the treatment of heart failure (HF) for over 200 years. However, digitalis toxicity-related death in HF patients undermines the beneficial effect of digitalis treatment. Digitalis-induced Na+ accumulation results in an increase in Ca2+i via the reverse mode of the Na+/Ca2+ exchanger (NCX) leading to enhanced SR Ca2+ load. The resulting increase in SR Ca2+ load would then be responsible for the positive inotropic effect and the toxic arrhythmogenic effects of glycosides. Digitalis-induced increase in Ca2+i could also activate CaMKII which has been shown to have proarrhythmic effects. Here we investigate whether CaMKII underlies glycoside arrhythmic effects and if so, which are the subcellular mechanisms involved. In electrically paced rat ventricular myocytes (0.5 Hz), 50 µM ouabain increased contraction amplitude by 160 ± 5%. Continued exposure to ouabain resulted in spontaneous contractile activity and Ca2+ waves which persisted even in the absence of electrical stimulation. Ouabain treatment was associated with activation of CaMKII (P-CaMKII) and phosphorilation of CaMKII downstream targets, site Tr17 of phospholamban and site Tr 2815 of the ryanodine receptor (RyR). Ouabain-induced spontaneous activity was prevented by inhibition of CaMKII with 1 µM KN93 but not by 1 µM of the inactive analogue KN92. Similar results were obtained using the structurally different CaMKII inhibitor, AIP (1-2.5µM). Ouabain treatment was associated with an increase in SR Ca2+ content and Ca2+ spark frequency, indicative of enhanced SR Ca2+ leak. KN93 suppressed the ouabain-induced increase in Ca2+ spark frequency without affecting SR content. These results suggest that CaMKII mediates ouabain-induced arrhythmic/toxic effects probably by phophorylating its SR targets. We speculate that CaMKII mediated phosphorylation of the RyR resulting Ca2+ leak from the SR could be the underlying mechanism involved.

Skeletal myotube formation enhanced by electrospun polyurethane carbon nanotube scaffolds.

BackgroundThis study examined the effects of electrically conductive materials made from electrospun single- or multiwalled carbon nanotubes with polyurethane to promote myoblast differentiation into myotubes in the presence and absence of electrical stimulation.Methods and resultsAfter electrical stimulation, the number of multinucleated myotubes on the electrospun polyurethane carbon nanotube scaffolds was significantly larger than that on nonconductive electrospun polyurethane scaffolds (5% and 10% w/v polyurethane). In the absence of electrical stimulation, myoblasts also differentiated on the electrospun polyurethane carbon nanotube scaffolds, as evidenced by expression of Myf-5 and myosin heavy chains. The myotube number and length were significantly greater on the electrospun carbon nanotubes with 10% w/v polyurethane than on those with 5% w/v polyurethane. The results suggest that, in the absence of electrical stimulation, skeletal myotube formation is dependent on the morphology of the electrospun scaffolds, while with electrical stimulation it is dependent on the electrical conductivity of the scaffolds.ConclusionThis study indicates that electrospun polyurethane carbon nanotubes can be used to modulate skeletal myotube formation with or without application of electrical stimulation.

Long-Lasting Intrinsic Optical Changes Observed in the Neurointermediate Lobe of the Mouse Pituitary Reflect Volume Changes in Cells of the Pars Intermedia

Background/Aims: Complex intrinsic optical changes (light scattering) are readily observed in the neurointermediate lobe of the mouse pituitary gland following electrical stimulation of the infundibular stalk. Our laboratory has previously identified three distinct phases within the light scattering signal: two rapid responses to action potential stimulation and a long duration recovery. The rapid light scattering signals, restricted to the neurohypophysial portion (posterior pituitary) of the neurointermediate lobe, consist of an E-wave and an S-wave that reflect excitation and secretion, respectively. The E-wave has the approximate shape of the action potential and includes voltage- and current-related components and is independent of Ca²⁺ entry. The S-wave is related to Ca²⁺ entry and exocytosis. The slow recovery phase of the light scattering signal, which we designated the R-wave, is less well characterized. Methods: Using high temporal resolution light scattering measurements, we monitored intrinsic optical changes in the neurointermediate lobe of the mouse pituitary gland. Pharmacological interventions during the measurements were employed. Results: The data presented here provide optical and pharmacological evidence suggesting that the R-wave, which comprises signals from the posterior pituitary as well as from the pars intermedia, mirrors volume changes in pars intermedia cells following a train of stimuli applied to the infundibular stalk. These volume changes were blocked by the GABA-receptor antagonists bicuculline and picrotoxin, and were mimicked by direct application of GABA in the absence of electrical stimulation. Conclusions: These results emphasize the importance of central GABAergic projections into the neurointermediate lobe, and the potential role of GABA in effecting hormone release from the pars intermedia.