Explore the vast range of titles available.

In traditional studies of changes in cell membrane potential or trans-membrane currents a large part of the recorded data presents \"a pure noise.\" This noise results mainly from the random openings of membrane ionic channels. Different types of stationary or non-stationary noise analysis have been used in electrophysiological experiments for identification of channels kinetic states. But these methods have a limited power and often cannot answer to the main question of the experimental study: do external factors induce a significant change of channels kinetics? A new method suggested in the current study is based on the scaling properties of the beta-distribution function that allows reducing the series containing 200,000 and more data points to analysis of only 10-20 stable parameters. The following clusterization using the generalized Pearson correlation function allows taking into account the influence of an external factor and combine/separate different parameters of interest into a statistical cluster considering the influential parameter. This method which we call BRC (Beta distribution-Reduction-Clusterization) opens new possibilities in creation of a largely reduced database while extracting specific fingerprints of the long-term series. The BRC method was validated using patch clamp current recordings containing 250,000 data points obtained from the living cells and from open tip electrode. The numerical distinction between these two series in terms of the reduced parameters was obtained.

Time-current characteristics for membrane systems with bacterial cellulose membranes located in horizontal plane and with NaCl solutions, indicate a stable formation of concentration boundary layers near the membrane for the configuration with a solution of lower concentration and lower density above the membrane (A). In turn, for the configuration with a higher concentration above the membrane (B) and a sufficiently large initial concentration quotient on the membrane (( C h / C l ) o ) current pulsations are observed over time, resulting from hydrodynamic instabilities occurring in the vicinity of the membrane. The increase of ( C h / C l ) o in configuration B causes an increase in the frequency of current pulsations and a change in their amplitudes. Furthermore, significant differences were observed between the types of the temporal changes in membrane currents in both configurations. The currents measured in steady states after 24 hours show differences between A and B configurations for ( C h / C l ) o > 500. Fast Fourier Transform (FFT) used to analyze the hydrodynamic instabilities in the range of observed pulsations of the measured currents shows that the average signal power of currents in the frequency range from 0.05 to 1 min -1 , depends non-linearly on the initial concentration quotient on the membrane, showing a maximum for the ( C h / C l ) o equal to 2500. In turn, the Short Time Fourier Transform (STFT) applied to the current signal as well as to the current difference signal (time lag equal to 1 min.) showed better resolution of the hydrodynamic instability analysis for the current difference signal. The increase of ( C h / C l ) o in the membrane system causes a gradual increase in STFT amplitudes towards longer times and higher frequencies. In turn, significant activity of hydrodynamic instabilities was observed in the first 50 min of current measurements for ( C h / C l ) o > 2500, followed by suppression of these instabilities.

This study presents a one-dimensional bidomain cable model for analyzing the relationship between rod membrane currents and rod electroretinogram (ERG) waveform components. The model incorporates the detailed structural and electrophysiological properties of rod photoreceptors by assuming the distribution of various ion currents. Simulation results indicate that the outer segment current ( I photo ) primarily influences the photoreceptor component of ERG in low-intensity light, while the transient potential notch shape called “nose,” observed under high-intensity light stimulation, is mainly attributed to the I h current in the inner segment. In addition, capacitive currents in the outer segment play a crucial role in maintaining extracellular current loops when I photo is inactive. These findings highlight that currents other than I photo , such as I h and capacitive currents, contribute significantly to the ERG waveform, particularly under high-intensity light, as theoretically suggested by Robson et al. The model successfully reproduced the experimentally measured rod ERG waveforms and their local components, providing a foundational platform for further investigation of ERG mechanisms. This enhanced understanding could lead to improved clinical applications of ERG in the diagnosis and assessment of retinal conditions. Future work will focus on refining the ion channel distribution, incorporating additional transport mechanisms, and validating the model using a broader range of experimental data to better replicate the complex electrophysiological phenomena of rod photoreceptor cells.

Ketamine is widely used as an anesthetic agent, yet its cellular effects on the auditory system, particularly on cochlear outer hair cells (OHCs), remain incompletely understood. In this study, we investigated the electrophysiological effects of ketamine on isolated OHCs from young Sprague Dawley rats using whole-cell patch-clamp techniques. OHCs were acutely dissociated and exposed to ketamine at varying concentrations to evaluate its impact on membrane currents. Ketamine produced a dose- and voltage-dependent reduction in outward membrane currents, particularly at membrane potentials more positive than –36 mV. Pharmacological blockade with iberiotoxin and ion substitution experiments using intracellular Cs + support that the ketamine-sensitive current is predominantly mediated by BK-like Ca 2+ -activated K + channels. Ketamine had minimal effects on resting membrane potential and on voltage-activated K + currents at hyperpolarized potentials, indicating selective modulation of depolarization-activated conductances. Acetylcholine (ACh)-evoked outward currents recorded at a depolarized holding potential (+ 3 mV) were not significantly altered by ketamine. Under these conditions, the measured current primarily reflects secondary Ca 2+ -activated K + channel activity rather than direct α9α10 nicotinic receptor-mediated currents. Therefore, the present experimental design does not allow determination of whether ketamine directly affects α9α10 receptor function. These findings demonstrate that ketamine modulates BK-like potassium currents in OHCs and may influence cochlear electrophysiological function. However, the precise mechanism—whether through direct channel interaction or indirect modulation via calcium signaling—remains to be determined.

Gap junction channels (GJCs) and hemichannels (HCs) are composed of protein subunits termed connexins (Cxs) and are permeable to ions and small molecules. In most organs, GJCs communicate the cytoplasm of adjacent cells, while HCs communicate the intra and extracellular compartments. In this way, both channel types coordinate physiological responses of cell communities. Cx mutations explain several genetic diseases, including about 50% of autosomal recessive nonsyndromic hearing loss. However, the possible involvement of Cxs in the etiology of acquired hearing loss remains virtually unknown. Factors that induce post-lingual hearing loss are diverse, exposure to gentamicin an aminoglycoside antibiotic, being the most common. Gentamicin has been proposed to block GJCs, but its effect on HCs remains unknown. In this work, the effect of gentamicin on the functional state of HCs was studied and its effect on GJCs was reevaluated in HeLa cells stably transfected with Cxs. We focused on Cx26 because it is the main Cx expressed in the cochlea of mammals where it participates in purinergic signaling pathways. We found that gentamicin applied extracellularly reduces the activity of HCs, while dye transfer across GJCs was not affected. HCs were also blocked by streptomycin, another aminoglycoside antibiotic. Gentamicin also reduced the ATP release and the HC-dependent oscillations of cytosolic free-Ca2+ signal. Moreover, gentamicin drastically reduced the Cx26 HC-mediated membrane currents in Xenopus laevis oocytes. Therefore, the extracellular gentamicin-induced inhibition of Cx HCs may adversely affect autocrine and paracrine signaling, including the purinergic one, which might partially explain its ototoxic effects.

Decision making frequently depends on monitoring the duration of sensory events. To determine whether, and how, the perception of elapsed time derives from the neuronal representation of the stimulus itself, we recorded and optogenetically modulated vibrissal somatosensory cortical activity as male rats judged vibration duration. Perceived duration was dilated by optogenetic excitation. A second set of rats judged vibration intensity; here, optogenetic excitation amplified the intensity percept, demonstrating sensory cortex to be the common gateway both to time and to stimulus feature processing. A model beginning with the membrane currents evoked by vibrissal and optogenetic drive and culminating in the representation of perceived time successfully replicated rats’ choices. Time perception is thus as deeply intermeshed within the sensory processing pathway as is the sense of touch itself, suggesting that the experience of time may be further investigated with the toolbox of sensory coding. The neural substrates of time perception are still unclear. Here, the authors show that as rats judged tactile stimuli, optogenetic manipulation of somatosensory cortex systematically altered perception of stimulus intensity and of duration, unveiling a multiplexed code.

Guanosine (GUO), widely considered a key signaling mediator, is implicated in the regulation of several cellular processes. While its interaction with neural membranes has been described, GUO still is an orphan neuromodulator. It has been postulated that GUO may eventually interact with potassium channels and adenosine (ADO) receptors (ARs), both particularly important for the control of cellular excitability. Accordingly, here, we investigated the effects of GUO on the bioelectric activity of human neuroblastoma SH-SY5Y cells by whole-cell patch-clamp recordings. We first explored the contribution of voltage-dependent K+ channels and, besides this, the role of ARs in the regulation of GUO-dependent cellular electrophysiology. Our data support that GUO is able to specifically modulate K+-dependent outward currents over cell membranes. Importantly, administering ADO along with GUO potentiates its effects. Overall, these results suggested that K+ outward membrane channels may be targeted by GUO with an implication of ADO receptors in SH-SY5Y cells, but also support the hypothesis of a functional interaction of the two ligands. The present research runs through the leitmotif of the deorphanization of GUO, adding insight on the interplay with adenosinergic signaling and suggesting GUO as a powerful modulator of SH-SY5Y excitability.

Spondylometaphyseal Dysplasia, Kozlowski Type (SMDK) is an autosomal dominant skeletal disorder characterized by marked scoliosis, platyspondyly, overfaced pedicles, and mild metaphyseal changes. Pathogenic variants in TRPV4, which encodes a calcium-permeable nonselective cation channel, are known to underlie SMDK. In this study, we identified a previously unreported missense variant in NM_021625.5( TRPV4 ): c.2354G > C (p.Trp785Ser), in a patient clinically diagnosed with SMDK. This variant affects a highly conserved residue and is predicted to alter protein conformation. Functional validation through cellular experiments revealed that the p.W785S substitution markedly reduces agonist-induced calcium influx and membrane currents, indicating a loss-of-function effect on TRPV4 channel activity. This deviates from the typical gain-of-function paradigm observed in most TRPV4-related skeletal dysplasias and may explain the relatively milder phenotype in our case. Our findings establish p.W785S as a novel pathogenic variant and highlight loss of TRPV4 activity as an alternative mechanism contributing to disease pathogenesis in SMDK.

Dilated cardiomyopathy (DCM) is a major risk factor for heart failure and is associated with the development of life-threatening cardiac arrhythmias. Using a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) model harbouring a mutation in cardiac troponin T (R173W), we aim to examine the cellular basis of arrhythmogenesis in DCM patients with this mutation. iPSC from control (Ctrl) and DCM-TnT-R173W donors from the same family were differentiated into iPSC-CM and analysed through optical action potential (AP) recordings, simultaneous measurement of cytosolic calcium concentration ([Ca2+]i) and membrane currents and separately assayed using field stimulation to detect the threshold for AP- and [Ca2+]i-alternans development. AP duration was unaltered in TnT-R173W iPSC-CM. Nevertheless, TnT-R173W iPSC-CM showed a strikingly low stimulation threshold for AP- and [Ca2+]i-alternans. Myofilaments are known to play a role as intracellular Ca2+ buffers and here we show increased Ca2+ affinity of intracellular buffers in TnT-R173W cells, indicating increased myofilament sensitivity to Ca2+. Similarly, EMD57033, a myofilament Ca2+ sensitiser, replicated the abnormal [Ca2+]i dynamics observed in TnT-R173W samples and lowered the threshold for alternans development. In contrast, application of a Ca2+ desensitiser (blebbistatin) to TnT-R173W iPSC-CM was able to phenotypically rescue Ca2+ dynamics, normalising Ca2+ transient profile and minimising the occurrence of Ca2+ alternans at physiological frequencies. This finding suggests that increased Ca2+ buffering likely plays a major arrhythmogenic role in patients with DCM, specifically in those with mutations in cardiac troponin T. In addition, we propose that modulation of myofilament Ca2+ sensitivity could be an effective anti-arrhythmic target for pharmacological management of this disease.

Microglia, the brain’s innate immune cells, have highly motile processes which constantly survey the brain to detect infection, remove dying cells, and prune synapses during brain development. ATP released by tissue damage is known to attract microglial processes, but it is controversial whether an ambient level of ATP is needed to promote constant microglial surveillance in the normal brain. Applying the ATPase apyrase, an enzyme which hydrolyzes ATP and ADP, reduces microglial process ramification and surveillance, suggesting that ambient ATP/ADP maintains microglial surveillance. However, attempting to raise the level of ATP/ADP by blocking the endogenous ecto-ATPase (termed NTPDase1/CD39), which also hydrolyzes ATP/ADP, does not affect the cells’ ramification or surveillance, nor their membrane currents, which respond to even small rises of extracellular [ATP] or [ADP] with the activation of K⁺ channels. This indicates a lack of detectable ambient ATP/ADP and ecto-ATPase activity, contradicting the results with apyrase. We resolve this contradiction by demonstrating that contamination of commercially available apyrase by a high K⁺ concentration reduces ramification and surveillance by depolarizing microglia. Exposure to the same K⁺ concentration (without apyrase added) reduced ramification and surveillance as with apyrase. Dialysis of apyrase to remove K⁺ retained its ATP-hydrolyzing activity but abolished the microglial depolarization and decrease of ramification produced by the undialyzed enzyme. Thus, applying apyrase affects microglia by an action independent of ATP, and no ambient purinergic signaling is required to maintain microglial ramification and surveillance. These results also have implications for hundreds of prior studies that employed apyrase to hydrolyze ATP/ADP.