Intracellular Dialysis Research Articles

Lipid mediator resolvin D2 inhibits ATP currents in rat primary sensory neurons.

Resolvin D2 (RvD2), an endogenous lipid mediator derived from docosahexaenoic acid, has been demonstrated to have analgesic effects. However, little is known about the mechanism underlying RvD2 in pain relief. Herein, we demonstrate that RvD2 targeted the P2X3 receptor as an analgesic. The electrophysiological activity of P2X3 receptors was suppressed by RvD2 in rat dorsal root ganglia (DRG) neurons. RvD2 pre-application dose-dependently decreased α,β-methylene-ATP (α,β-meATP)-induced inward currents. RvD2 remarkably decreased the maximum response to α,β-meATP, without influencing the affinity of P2X3 receptors. RvD2 also voltage-independently suppressed ATP currents. An antagonist of the G protein receptor 18 (GPR18), O-1918, prevented the RvD2-induced suppression of ATP currents. Additionally, intracellular dialysis of the Gαi/o-protein antagonist pertussis toxin (PTX), the PKA antagonist H89, or the cAMP analog 8-Br-cAMP also blocked the RvD2-induced suppression. Furthermore, α,β-meATP-triggered depolarization of membrane potential along with the action potential bursts in DRG neurons were inhibited by RvD2. Lastly, RvD2 attenuated spontaneous nociceptive behaviors as well as mechanical allodynia produced by α,β-meATP in rats via the activation of the peripheral GPR18. These findings indicated that RvD2 inhibited P2X3 receptors in rat primary sensory neurons through GPR18, PTX-sensitive Gαi/o-proteins, and intracellular cAMP/PKA signaling, revealing a novel mechanism that underlies its analgesic effects by targeting P2X3 receptors.

A1 Adenosine Receptor Activation Inhibits P2X3 Receptor-Mediated ATP Currents in Rat Dorsal Root Ganglion Neurons.

Purinergic signaling is involved in multiple pain processes. P2X3 receptor is a key target in pain therapeutics, while A1 adenosine receptor signaling plays a role in analgesia. However, it remains unclear whether there is a link between them in pain. The present results showed that the A1 adenosine receptor agonist N6-cyclopentyladenosine (CPA) concentration dependently suppressed P2X3 receptor-mediated and α,β-methylene-ATP (α,β-meATP)-evoked inward currents in rat dorsal root ganglion (DRG) neurons. CPA significantly decreased the maximal current response to α,β-meATP, as shown a downward shift of the concentration-response curve for α,β-meATP. CPA suppressed ATP currents in a voltage-independent manner. Inhibition of ATP currents by CPA was completely prevented by the A1 adenosine receptor antagonist KW-3902, and disappeared after the intracellular dialysis of either the Gi/o protein inhibitor pertussis toxin, the adenylate cyclase activator forskolin, or the cAMP analog 8-Br-cAMP. Moreover, CPA suppressed the membrane potential depolarization and action potential bursts, which were induced by α,β-meATP in DRG neurons. Finally, CPA relieved α,β-meATP-induced nociceptive behaviors in rats by activating peripheral A1 adenosine receptors. These results indicated that CPA inhibited the activity of P2X3 receptors in rat primary sensory neurons by activating A1 adenosine receptors and its downstream cAMP signaling pathway, revealing a novel peripheral mechanism underlying its analgesic effect.

On the accuracy of cell-attached current-clamp recordings from cortical neurons.

Cell-attached current-clamp (CA/CC) recordings have been proposed to measure resting membrane potential and synaptic/agonist responses in neurons without disrupting the cell membrane, thus avoiding the intracellular dialysis that occurs in conventional whole-cell recordings (WC). However, the accuracy of CA/CC recordings in neurons has not been directly assessed. Here, we used concomitant CA and WC current clamp recordings from cortical neurons in brain slices. Resting membrane potential values and slow voltage shifts showed variability and were typically attenuated during CA/CC recordings by ~10–20% relative to WC values. Fast signals were slowed down and their amplitude was greatly reduced: synaptic potentials by nearly 2-fold, and action potentials by nearly 10-fold in CA/CC mode compared to WC. The polarity of GABAergic postsynaptic responses in CA/CC mode matched the responses in WC, and depolarising GABAergic potentials were predominantly observed during CA/CC recordings of intact neonatal CA3 hippocampal pyramidal neurons. Similarly, CA/CC recordings reliably detected neuronal depolarization and excitation during network-induced giant depolarizing potentials in the neonatal CA3 hippocampus, and revealed variable changes, from depolarization to hyperpolarization, in CA1 pyramidal cells during sharp wave ripples in the adult hippocampus. Thus, CA/CC recordings are suitable for assessing membrane potential but signal distortion, probably caused by leakage via the seal contact and RC filtering should be considered.

Enhancement of P2X3 Receptor-Mediated Currents by Lysophosphatidic Acid in Rat Primary Sensory Neurons.

Lysophosphatidic acid (LPA), a lipid metabolite, plays a role in both neuropathic and inflammatory pain through LPA1 receptors. P2X3 receptor has also been shown to participate in these pathological processes. However, it is still unclear whether there is a link between LPA signaling and P2X3 receptors in pain. Herein, we show that a functional interaction between them in rat dorsal root ganglia (DRG) neurons. Pretreatment of LPA concentration-dependently enhanced α,β-methylene-ATP (α,β-meATP)-induced inward currents mediated by P2X3 receptors. LPA significantly increased the maximal current response of α,β-meATP, showing an upward shift of the concentration-response curve for α,β-meATP. The LPA enhancement was independent on the clamping-voltage. Enhancement of P2X3 receptor-mediated currents by LPA was prevented by the LPA1 receptor antagonist Ki16198, but not by the LPA2 receptor antagonist H2L5185303. The LPA-induced potentiation was also attenuated by intracellular dialysis of either G-protein inhibitor or protein kinase C (PKC) inhibitor, but not by Rho inhibitor. Moreover, LPA significantly changed the membrane potential depolarization and action potential burst induced by α,β-meATP in DRG neurons. Finally, LPA exacerbated α,β-meATP- induced nociceptive behaviors in rats. These results suggested that LPA potentiated the functional activity of P2X3 receptors in rat primary sensory neurons through activation of the LPA1 receptor and its downstream PKC rather than Rho signaling pathway, indicating a novel peripheral mechanism underlying the sensitization of pain.

The inhibitory effect of α-methyl-5-HT on ATP-activated currents in rat dorsal root ganglion neurons

Abstract The purpose of this study was to explore the inhibitory effect of α-methyl-5- hydroxytryptamine (α-methyl-5-HT) on ATP-activated current (IATP) in rat dorsal root ganglion (DRG) neurons. Whole-cell patch clamp experiment was performed on cultured rat DRG neurons. One minute after treatment with α-methyl-5-HT, ATP (10-4 mol/L) activation current in rat DRG neurons was inhibited. However, this inhibitory effect was independent of the current caused by α-methyl-5-HT. The dose-response curve for IATP showed that α-methyl-5-HT significantly shifted it. The Kd values of ATP-activated currents before and after the pre-addition of α-methyl-5-HT were similar (4.23×10-5 mol/L vs. 6.81×10-5 mol/L). Furthermore, cyproheptadine (10-6 mol/L), an antagonist of 5-HT2 receptor, can reverse the inhibition of α-methyl-5-HT. After intracellular dialysis of KN93 (CaMKII inhibitor) and H7 (PKC inhibitor), this inhibition was also completely eliminated. In conclusion, our results showed that α-methyl-5-HT inhibited ATP-activated current through activating the 5-HT2 receptor and resulting in phosphorylation of the ATP receptor. It was caused by the activation of G protein coupled receptor and corresponding intracellular signaling transduction cascade.

Glycine Release Is Potentiated by cAMP via EPAC2 and Ca2+ Stores in a Retinal Interneuron.

Neuromodulation via the intracellular second messenger cAMP is ubiquitous at presynaptic nerve terminals. This modulation of synaptic transmission allows exocytosis to adapt to stimulus levels and reliably encode information. The AII amacrine cell (AII-AC) is a central hub for signal processing in the mammalian retina. The main apical dendrite of the AII-AC is connected to several lobular appendages that release glycine onto OFF cone bipolar cells and ganglion cells. However, the influence of cAMP on glycine release is not well understood. Using membrane capacitance measurements from mouse AII-ACs to directly measure exocytosis, we observe that intracellular dialysis of 1 mm cAMP enhances exocytosis without affecting the L-type Ca2+ current. Responses to depolarizing pulses of various durations show that the size of the readily releasable pool of vesicles nearly doubles with cAMP, while paired-pulse depression experiments suggest that release probability does not change. Specific agonists and antagonists for exchange protein activated by cAMP 2 (EPAC2) revealed that the cAMP-induced enhancement of exocytosis requires EPAC2 activation. Furthermore, intact Ca2+ stores were also necessary for the cAMP potentiation of exocytosis. Postsynaptic recordings from OFF cone bipolar cells showed that increasing cAMP with forskolin potentiated the frequency of glycinergic spontaneous IPSCs. We propose that cAMP elevations in the AII-AC lead to a robust enhancement of glycine release through an EPAC2 and Ca2+ store signaling pathway. Our results thus contribute to a better understanding of how AII-AC crossover inhibitory circuits adapt to changes in ambient luminance.SIGNIFICANCE STATEMENT The mammalian retina operates over a wide dynamic range of light intensities and contrast levels. To optimize the signal-to-noise ratio of processed visual information, both excitatory and inhibitory synapses within the retina must modulate their gain in synaptic transmission to adapt to different levels of ambient light. Here we show that increases of cAMP concentration within AII amacrine cells produce enhanced exocytosis from these glycinergic interneurons. Therefore, we propose that light-sensitive neuromodulators may change the output of glycine release from AII amacrine cells. This novel mechanism may fine-tune the amount of tonic and phasic synaptic inhibition received by bipolar cell terminals and, consequently, the spiking patterns that ganglion cells send to the upstream visual areas of the brain.

High fat diet induces change in mitochondria respiration, activation of K-ATP channel and action potential shortening in mice

Obesity is associated with an increased risk of atrial fibrillation (AF). This epidemiologic observation may not be only due to shared co-morbidities but also from direct impacts of metabolic disorders on myocardium. To examine the impact of high fat diet (HFD) induced obesity on electrical properties in mice atria. Eight weeks old C57Bl/6 J mice were subjected to 4 months of HFD (60% fat) or normal diet (ND, 4% fat). Rapid burst atrial pacing were delivered using a trans-esophageal probe to induced AF in anesthetized animals. Action potential (AP) were recorded in left atrium using glass microelectrode technique. Potassium currents were recorded in isolated atrial myocytes using whole cell or perforated patch-clamp configurations. Mitochondrial respiration was studied in saponin-permeabilized atrial muscle fibers using a Clarke electrode. HFD mice showed higher atrial vulnerability to AF as indicated by longer AF episodes. APs were shorter in HFD versus ND mice (AP duration measured at 90% of repolarization: 49.3 ± 1.6 msec in HFD vs. 56.7 ± 2.3 msec in ND, P < 0.01). Glibenclamide, a KATP channel blocker, reversed AP shortening whereas cromakalim, a KATP channel activator, had no effect. Only in perforated patch-clamp configuration, without intracellular dialysis, KATP component of potassium current was enhanced in HFD mice (at +70 mV: 0.41 ± 0.12 pA/pF in HFD vs. 0.13 ± 0.08 pA/pF in ND, P < 0.05). There was no change in mitochondria respiration capacity between ND and HFD, however the ability of palmitoyl-CoA to support mitochondrial respiration was higher in HFD (25.99 ± 4.11% vs. 46.9 ± 3.96% in ND, P = 0.001). In addition, HADHA activity was enhanced in HFD mice. Obesity in mice is associated with atrial AP shortening which appears to result from increased activity of KATP-regulated currents and be associated with a metabolic shift. Shortening of AP duration could contribute to higher vulnerability to AF during obesity.

Mitochondria Influence NMDA Receptor‐mediated Currents in Hypothalamic Magnocellular Neurons: Altered Mechanisms during Heart Failure

Hypothalamic magnocellular neurosecretory neurons (MNNs) located in the supraoptic (SON) and paraventricular nuclei (PVN) play a critical role in the pathophysiology of heart failure (HF). Mitochondria (MITO) plays an important role in the regulation of intracellular Ca2+ dynamics, and several studies observed that morphological and functional MITO changes contribute to the development and maintenance of various brain diseases. We recently demonstrated that NMDA receptors activation triggers a Ca2+−dependent stimulation of SK channel in MNNs from Sham rats, and that this coupling acts as a negative feedback mechanism restraining the magnitude of the NMDA receptor‐mediated current (INMDAR) and its excitatory effects. Importantly, we found that the NMDA‐SK channel coupling is blunted in MNNs from HF rats. Still, whether MITO regulation of intracellular Ca2+ dynamics influence INMDAR and whether this effect is altered during HF is unknown. To address this question, we obtained whole‐cell patch clamp recordings from MNNs (holding potential: −50 mV) in slices from Sham and HF rats. We found that focal application of NMDA (50 μM, 300 ms) evoked an INMDAR whose magnitude was similar in Sham and HF rats (p&gt;0.05), as previously reported. Application of CCCP (10 μM, 5 s), a mitochondrial uncoupler, significantly increased the evoked INMDAR in MNNs from Sham rats (p&lt;0.05), but had no effect in MNNs from HF rats (p&gt;0.05). Intracellular dialysis of MNNs with the Ca2+ chelator BAPTA (10 mM) significantly augmented INMDAR in MNNs from Sham rats compared to the control condition (p&lt;0.05), and occluded the CCCP‐induced INMDAR increase. Taken together, our data supports that mitochondria regulate, in a Ca2+‐dependent manner, the magnitude of INMDAR in MNNs from Sham rats, a phenomenon that is blunted during HF.Support or Funding InformationR01HL090948

Somatostatin receptor 5-mediated modulation of outward K+ currents in rat retinal ganglion cells.

Somatostatin participants in multiple physiological functions by activating the five distinct G-protein-coupled receptors (sst1-sst5). In this study, we investigated the effect of sst5 activation on outward K currents in acutely isolated rat retinal ganglion cells using whole-cell patch-clamp techniques. Extracellular application of L-817,818, a specific sst5 agonist, significantly reduced outward K currents which was mainly the 4-aminopyridine and glybenclamide sensitive current components, but not the tetraethylammonium-sensitive one. The L-817,818 effect was mediated by sst5 since the suppression was eliminated when intracellular dialysis of the G-protein inhibitor GDP-β-S or extracellular application of the sst5 antagonist BIM-23056. Intracellular phospholipase C/protein kinase C signaling pathway was involved in the L-817,818 effect because the L-817,818 effect on K currents was inhibited when rat retinal ganglion cells were pretreated with U73122 or chelerythrine chloride. However, L-817,818 persisted to reduce the K currents when cAMP/protein kinase A, calcium/calmodulin-dependent protein kinase II and mitogen-activated protein kinase/extracellular signal-regulated kinase signaling pathways were blocked respectively. These results suggest that sst5 activation suppresses 4-aminopyridine and glybenclamide-sensitive K currents in rat retinal ganglion cells by stimulating intracellular phospholipase C/protein kinase C signaling pathway, thereby regulating the rat retinal ganglion cell excitability.

Membranotropic activity of taurine derivatives

The aim of the work. To evaluate the effect of n-phenylalkyl derivatives of taurine on changes in transmembrane ion currents of potential-controlled ion channels of isolated neurons.&#x0D; Materials and methods. The method of intracellular dialysis and fixation of membrane potential on isolated neurons of the great pond truncatula (Lymnaea stagnalis) and hornbill (Planorbarius corneus) was used. The n-phenylalkyl derivatives of taurine (1-phenyl-2-isopropylaminoethanesulfonic acid; benzylaminoethane sulfonic acid isopropylamide; phenethylaminoethane sulfonic acid isopropylamide) or the comparison drug taurine was dissolved in external solutions and studied at concentrations of 1, 10, 100 and 1000 M.&#x0D; Results. The results demonstrate that n-phenilalkyl derivatives of taurine in low concentrations (1; 10 M) have a modulating effect on electrically excitable cells, and in high concentrations (100; 1000 M) reduce the sodium-calcium influx and potassium efflux ionic currents, have a channel blocking effect.&#x0D; Conclusion. N-phenylalkyl derivatives of taurine reduces the excitability of cells contribute to the suppression of synaptic potentials, ion gradients of the cells.

Squaring the Circle: A New Study of Inward and Outward-Rectifying Potassium Currents in U251 GBM Cells.

In the present study, the functional role of the inwardly rectifying K+ channel, Kir4.1, and large-conductance Ca2+-activated K+ (BK) channel during cell migration in U251 cell line was investigated. We focused on polarised cells which are positive for the active-Cdc42 migration marker. The perforated patch technique was used to avoid intracellular dialysis and to maintain physiological changes in intracellular calcium. Wound healing was employed to assay migration after 24h. Polarised cells recorded displayed different hallmarks of undifferentiated glial cells: depolarised resting membrane potential and high membrane resistance. Cells recorded outside wounded area did not display either constitutive inward or outward rectification. After migration, U251 cells were characterised by a constitutively smaller Kir4.1 and larger BK currents with a linearly related amplitude. Menthol modulation increased both currents in a linearly dependent manner, indicating a common mechanism triggered by activationof transient receptor potential melastatin 8 (TRPM8), a Ca2+-permeable non-selective cation channel. We hypothesised that both migration and menthol modulation would share an increase of intracellular calcium triggering the increase in Kir4.1 and BK channels. Immunocytochemistry demonstrated the cytoplasmic expression of both Kir4.1 and BK channels and a mislocation in the nucleus under basal conditions. Before and after migration, polarised cells increased the expression of Kir4.1 and BK channels both in the cytoplasm and nucleus. TEM ultrastructural analysis displayed a different nuclear distribution of Kir4.1 and BK channels. In the present study, the physiological role of Kir4.1 and BK currents at membrane potential, their involvement in migration, and the functional role of nuclear channels were discussed.

A novel phospho-modulatory mechanism contributes to the calcium-dependent regulation of T-type Ca2+ channels

Cav3 / T-type Ca2+ channels are dynamically regulated by intracellular Ca2+ ions, which inhibit Cav3 availability. Here, we demonstrate that this inhibition becomes irreversible in the presence of non-hydrolysable ATP analogs, resulting in a strong hyperpolarizing shift in the steady-state inactivation of the residual Cav3 current. Importantly, the effect of these ATP analogs was prevented in the presence of intracellular BAPTA. Additional findings obtained using intracellular dialysis of inorganic phosphate and alkaline phosphatase or NaN3 treatment further support the involvement of a phosphorylation mechanism. Contrasting with Cav1 and Cav2 Ca2+ channels, the Ca2+-dependent modulation of Cav3 channels appears to be independent of calmodulin, calcineurin and endocytic pathways. Similar findings were obtained for the native T-type Ca2+ current recorded in rat thalamic neurons of the central medial nucleus. Overall, our data reveal a new Ca2+ sensitive phosphorylation-dependent mechanism regulating Cav3 channels, with potentially important physiological implications for the multiple cell functions controlled by T-type Ca2+ channels.

Metabolic regulation of Kv channels and cardiac repolarization by Kvβ2 subunits

Voltage-gated potassium (Kv) channels control myocardial repolarization. Pore-forming Kvα proteins associate with intracellular Kvβ subunits, which bind pyridine nucleotides with high affinity and differentially regulate channel trafficking, plasmalemmal localization and gating properties. Nevertheless, it is unclear how Kvβ subunits regulate myocardial K+ currents and repolarization. Here, we tested the hypothesis that Kvβ2 subunits regulate the expression of myocardial Kv channels and confer redox sensitivity to Kv current and cardiac repolarization. Co-immunoprecipitation and in situ proximity ligation showed that in cardiac myocytes, Kvβ2 interacts with Kv1.4, Kv1.5, Kv4.2, and Kv4.3. Cardiac myocytes from mice lacking Kcnab2 (Kvβ2−/−) had smaller cross sectional areas, reduced sarcolemmal abundance of Kvα binding partners, reduced Ito, IK,slow1, and IK,slow2 densities, and prolonged action potential duration compared with myocytes from wild type mice. These differences in Kvβ2−/− mice were associated with greater P wave duration and QT interval in electrocardiograms, and lower ejection fraction, fractional shortening, and left ventricular mass in echocardiographic and morphological assessments. Direct intracellular dialysis with a high NAD(P)H:NAD(P)+ accelerated Kv inactivation in wild type, but not Kvβ2−/− myocytes. Furthermore, elevated extracellular levels of lactate increased [NADH]i and prolonged action potential duration in wild type cardiac myocytes and perfused wild type, but not Kvβ2−/−, hearts. Taken together, these results suggest that Kvβ2 regulates myocardial electrical activity by supporting the functional expression of proteins that generate Ito and IK,slow, and imparting redox and metabolic sensitivity to Kv channels, thereby coupling cardiac repolarization to myocyte metabolism.

Crosstalk between mitochondria, calcium channels and actin cytoskeleton modulates noradrenergic activity of locus coeruleus neurons.

Locus coeruleus (LC) is the name of a group of large sized neurons located at the brain stem, which provides the main source of noradrenaline to the central nervous system, virtually, innervating the whole brain. All noradrenergic signalling provided by this nucleus is dependent on an intrinsic pacemaker process. Our study aims to understand how noradrenergic neurons finely tune their pacemaker processes and regulate their activities. Here we present that mitochondrial perturbation in the LC from mice, inhibits spontaneous firing by a hyperpolarizing response that involves Ca2+ entry via L-type Ca2+ channels and the actin cytoskeleton. We found that pharmacological perturbation of mitochondria from LC neurons using the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP), induced a dominant hyperpolarizing response when electrophysiological approaches were performed. Surprisingly, the CCCP-induced hyperpolarizing response was dependent on L-type Ca2+ channel-mediated Ca2+ entry, as it was inhibited by: the removal of extracellular Ca2+ ; the addition of Cd2+ ; nifedipine or nicardipine; but not by the intracellular dialysis with the Ca2+ chelator 1,2-Bis(2-Aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, the latter indicating that the response was not because of a global change in [Ca2+ ]c but does not exclude action at intracellular microdomains. Further to this, the incubation of slices with cytochalasin D, an agent that depolymerises the actin cytoskeleton, inhibited the hyperpolarizing response indicating an involvement of the actin cytoskeleton. The data are consistent with the hypothesis that there is a crosstalk between mitochondria and L-type Ca2+ channels leading to modulation of noradrenergic neuronal activity mediated by the actin cytoskeleton. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Inhibition of ICa,L by DHEA in Aortic Smooth Muscle Cells: Voltage‐dependency, Modulation by GPCR Signaling and Inhibition of Glucose‐6‐phosphate Dehydrogenase

Dehydroepiandrosterone (DHEA) is a hormone abundantly released from adrenal cortex as DHEA‐sulfate (DHEA‐S). DHEA‐S is released also in brain. DHEA and epiandrosterone (EPI), a metabolite of DHEA, produces relaxation of high‐K+ induced contraction of aortic smooth muscle (ASM). EPI increases voltage‐dependent inactivation (voltage‐dependent inhibition, VDI) of ICa,L in ventricular myocytes. Whole‐cell ICa,L was recorded as IBa from ASM cells (ASMCs) of A7r5 cell line and enzymatically isolated bovine coronary ASMCs to study mechanism and modulation of DHEA‐induced inhibition of ICa,L. DHEA produced VDI; acceleration of time course of inactivation, increase of inhibition by depolarization of holding potential (HP) and leftward shift of steady state inactivation curve; f∞, 2s‐V, obtained by 2 s conditioning pulse and f∞, HP‐V as a function HP. In addition, DHEA produced voltage‐independent inhibition (VIDI) represented by inhibition of peak amplitude (ICa,L,peak) of ICa,L elicited by pulses from hyperpolarized HPs. Window ICa,L (IWD) supplies Ca2+ in the E‐C coupling of ASM. IWD obtained from I–V of ICa,L,peak and f∞, HP‐V fitted well with recorded IWD and they were strongly inhibited by DHEA. Efficacy of DHEA‐induced VDI was reduced by rightward shift of f∞, 2s‐V curve produced by depletion of cholesterol by MβCD. Blocking of GPCR signaling by intracellular dialysis of GDP‐β‐S also shifted f∞, 2s‐V to the right and it produced decrease of DHEA‐induced inhibition of ICa,L at depolarized HP (VDI). DHEA and EPI are inhibitors of glucose‐phosphate‐dehydrogenase (G6PD), a redox‐related pentose‐phosphate pathway enzyme. 6‐Aminonicotinamide (6‐AN), another inhibitor of G6PD produced VIDI without inducing VDI. DHEA‐S that does not inhibit G6PD induced small but significant VDI at an order higher concentration of DHEA without generating VIDI. GPCR signaling and membrane cholesterol are indirectly involved in the modulation of DHEA‐induced VDI by affecting basal voltage‐dependent inactivation. The occurrence of VIDI by 6‐AN indicates that G6PD inhibition underlies DHEA‐induced VIDI. DHEA‐induced inhibition of IWD by VDI and VIDI contributes for DHEA‐induced relaxation of ASM.Support or Funding InformationNational Heart, Lung, and Blood Institute Grant RO1 HL‐085352 to S. A. Gupte.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Kir2.1-Nav1.5 Channel Complexes Are Differently Regulated than Kir2.1 and Nav1.5 Channels Alone.

Cardiac Kir2.1 and Nav1.5 channels generate the inward rectifier K+ (IK1) and the Na+ (INa) currents, respectively. There is a mutual interplay between the ventricular INa and IK1 densities, because Nav1.5 and Kir2.1 channels exhibit positive reciprocal modulation. Here we compared some of the biological properties of Nav1.5 and Kir2.1 channels when they are expressed together or separately to get further insights regarding their putative interaction. First we demonstrated by proximity ligation assays (PLAs) that in the membrane of ventricular myocytes Nav1.5 and Kir2.1 proteins are in close proximity to each other (<40 nm apart). Furthermore, intracellular dialysis with anti-Nav1.5 and anti-Kir2.1 antibodies suggested that these channels form complexes. Patch-clamp experiments in heterologous transfection systems demonstrated that the inhibition of the Ca2+/calmodulin-dependent protein kinase II (CaMKII) decreased the INa and the IK1 generated by Nav1.5 and Kir2.1 channels when they were coexpressed, but not the IK1 generated by Kir2.1 channels alone, suggesting that complexes, but not Kir2.1 channels, are a substrate of CaMKII. Furthermore, inhibition of CaMKII precluded the interaction between Nav1.5 and Kir2.1 channels. Inhibition of 14-3-3 proteins did not modify the INa and IK1 densities generated by each channel separately, whereas it decreased the INa and IK1 generated when they were coexpressed. However, inhibition of 14-3-3 proteins did not abolish the Nav1.5-Kir2.1 interaction. Inhibition of dynamin-dependent endocytosis reduced the internalization of Kir2.1 but not of Nav1.5 or Kir2.1-Nav1.5 complexes. Inhibition of cytoskeleton-dependent vesicular trafficking via the dynein/dynactin motor increased the IK1, but reduced the INa, thus suggesting that the dynein/dynactin motor is preferentially involved in the backward and forward traffic of Kir2.1 and Nav1.5, respectively. Conversely, the dynein/dynactin motor participated in the forward movement of Kir2.1-Nav1.5 complexes. Ubiquitination by Nedd4-2 ubiquitin-protein ligase promoted the Nav1.5 degradation by the proteasome, but not that of Kir2.1 channels. Importantly, the Kir2.1-Nav1.5 complexes were degraded following this route as demonstrated by the overexpression of Nedd4-2 and the inhibition of the proteasome with MG132. These results suggested that Kir2.1 and Nav1.5 channels closely interact with each other leading to the formation of a pool of complexed channels whose biology is similar to that of the Nav1.5 channels.

Противосудорожная и мембранотропная активность соединения РУ-1205

В тесте максимального электрошока на мышах через корнеальные электроды исследовали противосудорожную активность соединения РУ-1205 (дигидрохлорида 9-(2-морфолиноэтил)-2-(4-фторфенил)имидазо[1,2-a]бензимидазола) и препарата сравнения карбамазепина. ЭД50 соединения РУ-1205 и карбамазепина у мышей составили 11,4 и 14,1 мг/кг внутрибрюшинно соответственно. Антиэпилептиформную активность соединения РУ-1205 оценивали в условиях электрической стимуляции поверхности мозга крыс (с напряжением 120 В, частотой 10 Гц и длительностью 10 с). Вещество РУ-1205 в концентрации 23,7 мкМ эффективно предупреждало возникновение электроиндуцированной эпилептической активности и восстанавливало нормальный ритмогенез нейронных колонок соматосенсорной коры. На изолированных нейронах прудовика (Lymnaea stagnalis) с использованием метода внутриклеточного диализа и фиксации мембранного потенциала изучено влияние соединения РУ-1205 в концентрациях 1, 10, 100 и 1000 мкМ на натриевые (INa) и кальциевые (ICa) ионные токи. Исследуемое вещество обратимо подавляло натриевые (INa) и кальциевые (ICa) ионные токи максимально в концентрации 1000 мкМ на 77,0 и 58,7 % соответственно, p &lt; 0,05.

Metabolic inhibition reduces cardiac L-type Ca2+ channel current due to acidification caused by ATP hydrolysis.

Metabolic stress evoked by myocardial ischemia leads to impairment of cardiac excitation and contractility. We studied the mechanisms by which metabolic inhibition affects the activity of L-type Ca2+ channels (LTCCs) in frog ventricular myocytes. Metabolic inhibition induced by the protonophore FCCP (as well as by 2,4- dinitrophenol, sodium azide or antimycin A) resulted in a dose-dependent reduction of LTCC current (ICa,L) which was more pronounced during β-adrenergic stimulation with isoprenaline. ICa,L was still reduced by metabolic inhibition even in the presence of 3 mM intracellular ATP, or when the cell was dialysed with cAMP or ATP-γ-S to induce irreversible thiophosphorylation of LTCCs, indicating that reduction in ICa,L is not due to ATP depletion and/or reduced phosphorylation of the channels. However, the effect of metabolic inhibition on ICa,L was strongly attenuated when the mitochondrial F1F0-ATP-synthase was blocked by oligomycin or when the cells were dialysed with the non-hydrolysable ATP analogue AMP-PCP. Moreover, increasing the intracellular pH buffering capacity or intracellular dialysis of the myocytes with an alkaline solution strongly attenuated the inhibitory effect of FCCP on ICa,L. Thus, our data demonstrate that metabolic inhibition leads to excessive ATP hydrolysis by the mitochondrial F1F0-ATP-synthase operating in the reverse mode and this results in intracellular acidosis causing the suppression of ICa,L. Limiting ATP break-down by F1F0-ATP-synthase and the consecutive development of intracellular acidosis might thus represent a potential therapeutic approach for maintaining a normal cardiac function during ischemia.

External Ca2+ regulates polycystin-2 (TRPP2) cation currents in LLC-PK1 renal epithelial cells

Polycystin-2 (PC2, TRPP2) is a nonselective cation channel whose dysfunction is associated with the onset of autosomal dominant polycystic kidney disease (ADPKD). PC2 contributes to Ca2+ transport and cell signaling in renal epithelia and other tissues. Little is known however, as to the external Ca2+ regulation of PC2 channel function. In this study, we explored the effect of external Ca2+ on endogenous PC2 in wild type LLC-PK1 renal epithelial cells. We obtained whole cell currents at different external Ca2+ concentrations, and observed that the basal whole cell conductance in normal Ca2+(1.2mM), decreased by 30.2% in zero (nominal) Ca2+ and conversely, increased by 38% in high external Ca2+(6.2mM). The high Ca2+-increased whole cell currents were completely inhibited by either PC2 gene silencing, or intracellular dialysis with active, but not denatured by boiling, PC2 antibody. Exposure of cells to high Ca2+ was also associated with relocation of PC2 to the plasma membrane. To explore whether a Ca2+ sensing receptor (CaSR) was implicated in the external Ca2+ modulation of PC2 currents, we tested the effect of the CaSR agonists, spermine and the calcimimetic R-568, which largely mimicked the effect of high Ca2+ under Ca2+-free conditions. The CaSR agonist gentamicin also increased the PC2 currents in the presence of normal Ca2+. The presence of CaSR was confirmed by immunocytochemistry, which partially colocalized with the intracellular PC2 protein, in an external Ca2+-dependent manner. The data support a novel Ca2+ sensing mechanism for PC2 expression and functional regulation in renal epithelial cells.

AMP-activated protein kinase inhibits Kv 1.5 channel currents of pulmonary arterial myocytes in response to hypoxia and inhibition of mitochondrial oxidative phosphorylation.

Key points Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltage‐gated potassium channels (Kv) in pulmonary arterial smooth muscle by hypoxia, although the precise molecular mechanisms have been unclear.AMP‐activated protein kinase (AMPK) has been proposed to couple inhibition of mitochondrial metabolism by hypoxia to acute hypoxic pulmonary vasoconstriction and progression of pulmonary hypertension.Inhibition of complex I of the mitochondrial electron transport chain activated AMPK and inhibited Kv1.5 channels in pulmonary arterial myocytes.AMPK activation by 5‐aminoimidazole‐4‐carboxamide riboside, A769662 or C13 attenuated Kv1.5 currents in pulmonary arterial myocytes, and this effect was non‐additive with respect to Kv1.5 inhibition by hypoxia and mitochondrial poisons.Recombinant AMPK phosphorylated recombinant human Kv1.5 channels in cell‐free assays, and inhibited K+ currents when introduced into HEK 293 cells stably expressing Kv1.5.These results suggest that AMPK is the primary mediator of reductions in Kv1.5 channels following inhibition of mitochondrial oxidative phosphorylation during hypoxia and by mitochondrial poisons. Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltage‐gated potassium channels (Kv) in pulmonary arterial smooth muscle cells that is mediated by the inhibition of mitochondrial oxidative phosphorylation. We sought to determine the role in this process of the AMP‐activated protein kinase (AMPK), which is intimately coupled to mitochondrial function due to its activation by LKB1‐dependent phosphorylation in response to increases in the cellular AMP:ATP and/or ADP:ATP ratios. Inhibition of complex I of the mitochondrial electron transport chain using phenformin activated AMPK and inhibited Kv currents in pulmonary arterial myocytes, consistent with previously reported effects of mitochondrial inhibitors. Myocyte Kv currents were also markedly inhibited upon AMPK activation by A769662, 5‐aminoimidazole‐4‐carboxamide riboside and C13 and by intracellular dialysis from a patch‐pipette of activated (thiophosphorylated) recombinant AMPK heterotrimers (α2β2γ1 or α1β1γ1). Hypoxia and inhibitors of mitochondrial oxidative phosphorylation reduced AMPK‐sensitive K+ currents, which were also blocked by the selective Kv1.5 channel inhibitor diphenyl phosphine oxide‐1 but unaffected by the presence of the BKCa channel blocker paxilline. Moreover, recombinant human Kv1.5 channels were phosphorylated by AMPK in cell‐free assays, and K+ currents carried by Kv1.5 stably expressed in HEK 293 cells were inhibited by intracellular dialysis of AMPK heterotrimers and by A769662, the effects of which were blocked by compound C. We conclude that AMPK mediates Kv channel inhibition by hypoxia in pulmonary arterial myocytes, at least in part, through phosphorylation of Kv1.5 and/or an associated protein.