Intracellular Sodium Research Articles

SLC8 family of sodium/calcium exchangers in GtoPdb v.2021.3

The sodium/calcium exchangers (NCX) use the extracellular sodium concentration to facilitate the extrusion of calcium out of the cell. Alongside the plasma membrane Ca2+-ATPase (PMCA) and sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA), as well as the sodium/potassium/calcium exchangers (NKCX, SLC24 family), NCX allow recovery of intracellular calcium back to basal levels after cellular stimulation. When intracellular sodium ion levels rise, for example, following depolarisation, these transporters can operate in the reverse direction to allow calcium influx and sodium efflux, as an electrogenic mechanism. Structural modelling suggests the presence of 9 TM segments, with a large intracellular loop between the fifth and sixth TM segments [1].

Effect of handling on ATP utilization of cerebral Na,K-ATPase in rats with trimethyltin-induced neurodegeneration.

Previously it was shown that for reduction of anxiety and stress of experimental animals, preventive handling seems to be one of the most effective methods. The present study was oriented on Na,K-ATPase, a key enzyme for maintaining proper concentrations of intracellular sodium and potassium ions. Malfunction of this enzyme has an essential role in the development of neurodegenerative diseases. It is known that this enzyme requires approximately 50% of the energy available to the brain. Therefore in the present study utilization of the energy source ATP by Na,K-ATPase in the frontal cerebral cortex, using the method of enzyme kinetics was investigated. As a model of neurodegeneration treatment with trimethyltin (TMT) was applied. Daily handling (10min/day) of healthy rats and rats suffering neurodegeneration induced by administration of TMT in a dose of (7.5mg/kg), at postnatal days 60-102 altered the expression of catalytic subunits of Na,K-ATPase as well as kinetic properties of this enzyme in the frontal cerebral cortex of adult male Wistar rats. In addition to the previously published beneficial effect on spatial memory, daily treatment of rats was accompanied by improved maintenance of sodium homeostasis in the frontal cortex. The key system responsible for this process, Na,K-ATPase, was able to utilize better the energy substrate ATP. In rats, manipulation of TMT-induced neurodegeneration promoted the expression of the α2 isoform of the enzyme, which is typical for glial cells. In healthy rats, manipulation was followed by increased expression of the α3 subunit, which is typical of neurons.

Neuronal cells from bipolar individuals are more susceptible to glutamate induced apoptosis than cells from non-bipolar subjects

BackgroundBipolar disorder (BD) is associated with marked parenchymal brain loss in a significant fraction of patients. The lack of necrosis in postmortem examination suggests an apoptotic process. Emerging evidence suggests that mood stabilizers, like lithium, have antiapoptotic actions. Glutamatergic abnormalities have been associated with BD. MethodsOlfactory neuroepithelial progenitors (ONPs) harvested by biopsy from type I bipolar patients (BD-ONPs, n = 3) and non-bipolar controls (non-BD-ONPs, n = 6), were treated with glutamate at concentrations sufficient to mimic the observed doubling of intracellular sodium known to occur in both mania and bipolar depression, to investigate potential differential lithium effect on both BD-ONPs and non-BD-ONPs. ResultsApoptosis was detected in BP-ONPs exposed to 0.1 M glutamate for 6 h but in non-BD-ONPs at 24 h. Moreover, after treatment with 0.1 M glutamate treated for 6 h the levels of the pro-apoptotic cleaved-caspase-3 and cleaved-PARP proteins were significantly higher in BD-ONPs compare to non-BD-ONPs. Pretreatment with a therapeutic concentration of 1 mM lithium for 3 days attenuated the glutamate induced apoptosis. Lithium pretreatment 3 days also prevented the DNA fragmentation induced by glutamate, and significantly increased the antiapoptotic phospho-B-Raf and Bcl-2 proteins in BD-ONPs compared to non-BD-ONPs. LimitationsONPs are obtained from subjects with and without bipolar illness, but outcome of their study may still not reflect the biology of the illness. ConclusionsONPs derived from BD are more susceptible to glutamate-induced apoptosis. Lithium is associated with a greater increase of anti-apoptotic B-Raf and Bcl-2 expression in BD-ONPs.

Sodium Intensity Changes Differ Between Relaxation- and Density-Weighted MRI in Multiple Sclerosis.

Introduction: The source of Tissue Sodium Concentration (TSC) increase in Multiple Sclerosis (MS) remains unclear, and could be attributed to altered intracellular sodium concentration or tissue microstructure. This paper investigates sodium in MS using three new MRI sequences.Methods: Three sodium scans were acquired at 4.7 T from 30 patients (11 relapsing-remitting, 10 secondary-progressive, 9 primary-progressive) and 9 healthy controls including: Density-Weighted (NaDW), with very short 30° excitation for more accurate TSC measurement; Projection Acquisition with Coherent MAgNetization (NaPACMAN), designed for enhanced relaxation-based contrast; and Soft Inversion Recovery FLuid Attenuation (NaSIRFLA), developed to reduce fluid space contribution. Signal was measured in both lesions (n = 397) and normal appearing white matter (NAWM) relative to controls in the splenium of corpus callosum and the anterior and posterior limbs of internal capsule. Correlations with clinical and cognitive evaluations were tested over all MS patients.Results: Sodium intensity in MS lesions was elevated over control WM by a greater amount for NaPACMAN (75%) than NaDW (35%), the latter representing TSC. In contrast, NaSIRFLA exhibited lower intensity, but only for region specific analysis in the SCC (−7%). Sodium intensity in average MS NAWM was not significantly different than control WM for either of the three scans. NaSIRFLA in the average NAWM and specifically the posterior limb of internal capsules positively correlated with the Paced Auditory Serial Addition Test (PASAT).Discussion: Lower NaSIRFLA signal in lesions and ~2× greater NaPACMAN signal elevation over control WM than NaDW can be explained with a demyelination model that also includes edema. A NAWM demyelination model that includes tissue atrophy suggests no signal change for NaSIRFLA, and only slightly greater NAWM signal than control WM for both NaDW and NaPACMAN, reflecting experimental results. Models were derived from previous total and myelin water fraction study in MS with T2-relaxometry, and for the first time include sodium within the myelin water space. Reduced auditory processing association with lower signal on NaSIRFLA cannot be explained by greater demyelination and its modeled impact on the three sodium MRI sequences. Alternative explanations include intra- or extracellular sodium concentration change. Relaxation-weighted sodium MRI in combination with sodium-density MRI may help elucidate microstructural and metabolic changes in MS.

Crystalline silica induces macrophage necrosis and causes subsequent acute pulmonary neutrophilic inflammation.

Crystalline silica (CS), an airborne particulate, is a major global occupational health hazard. While it is known as an important pathogenic factor in many severe lung diseases, the underlying mechanisms of its toxicity are still unclear. In the present study, we found that intra-tracheal instillation of CS caused rapid emergence of necrotic alveolar macrophages. Cell necrosis was a consequence of the release of cathepsin B in CS-treated macrophages, which caused dysfunction of the mitochondrial membrane. Damage to mitochondria disrupted Na+/K+ ATPase activity in macrophages, leading to intracellular sodium overload and the subsequent cell necrosis. Further studies indicate that CS-induced macrophage necrosis and the subsequent release of mitochondrial DNA could trigger the recruitment of neutrophils in the lung, which was regulated by the TLR9 signaling pathway. In conclusion, our results suggest a novel mechanism whereby CS leads to rapid macrophage necrosis through cathepsin B release, following the leakage of mitochondrial DNA as a key event in the induction of pulmonary neutrophilic inflammation. This study has important implications for the early prevention and treatment of diseases induced by CS.

Na,K-ATPase α4, and Not Na,K-ATPase α1, is the Main Contributor to Sperm Motility, But its High Ouabain Binding Affinity Site is Not Required for Male Fertility in Mice.

Mammalian sperm express two Na,K-ATPase (NKA) isoforms, Na,K-ATPase α4 (NKAα4) and Na,K-ATPase α1 (NKAα1). While NKAα4 is critical to sperm motility, the role of NKAα1 in sperm movement remains unknown. We determined this here using a genetic and pharmacological approach, modifying the affinity of NKAα1 and NKAα4 for the inhibitor ouabain to selectively block the function of each isoform. Sperm from wild-type (WT) mice (naturally containing ouabain-resistant NKAα1 and ouabain-sensitive NKAα4) and three newly generated mouse lines, expressing both NKAα1 and NKAα4 ouabain resistant (OR), ouabain sensitive (OS), and with their ouabain affinity switched (SW) were used. All mouse lines produced normal sperm numbers and were fertile. All sperm types showed NKAα isoform expression levels and activity comparable to WT, and kinetics for ouabain inhibition confirming the expected changes in ouabain affinity for each NKA isoform. Ouabain at 1μM, which only block ouabain-sensitive NKA, significantly inhibited total, progressive, and hyperactivated sperm motility in WT and OS, but had no significant effect on OR or SW sperm. Higher ouabain (1mM), which inhibits both ouabain-sensitive and ouabain-resistant NKA, had little additional effect on sperm motility in all mouse lines, including the OR and SW. A similar pattern was found for the effect of ouabain on sperm intracellular sodium ([Na+]i). These results indicate that NKAα4, but not NKAα1 is the main contributor to sperm motility and that the ouabain affinity site in NKA is not an essential requirement for male fertility.

Biodegradable ion-selective nanosensors with p-diethylaminophenol functionalized rhodamine as chromoionophore for metal ions measurements

A new rhodamine derivative functionalized with a p-diethylaminophenol moiety together with two interacting pH-sensitive sites (PHX2) has been utilized as an electrically charged chromoionophore in ion-selective nano-optodes for the first time. The PHX2-based ion-selective nanosensors were prepared by a simple precipitation method with biodegradable polycaprolactone (PCL) and tributyl O-acetylcitrate (ATBC) as the polymer matrix. The obtained nanoparticles exhibited a hydrodynamic diameter of about 180 nm with water in oil conformation. The PHX2-based biodegradable nano-optodes can respond to pH from 5 to 12 in the presence of cation exchanger. Such nano-optodes were further applied to prepare fluorescent cation selective nano-optodes with incorporated ionophores based on ion-exchange sensing mechanism. For model ions Na+ and K+, the prepared nanosensors showed decreased absorbance intensity in the presence of the increasing ion concentrations. The cytotoxicity of Na+- and K+-selective nanosensors at the highest concentration for 24 h displayed above 85 % cell viability, indicating low toxicity and high biocompatibility. Chemically induced intracellular sodium concentration change in HepG2 cells was also successfully monitored in real time. The results proved that the new fluorescent chromoionophore was fully functional in ionophore-based biodegradable nano-optodes. Such biodegradable nanosensors appear to be promising in biomedical monitoring and disease therapy.

Impact of SGLT2 Inhibitors on Heart Failure: From Pathophysiology to Clinical Effects.

Heart failure (HF) affects up to over 20% of patients with type 2 diabetes (T2DM), even more in the elderly. Although, in T2DM, both hyperglycemia and the proinflammatory status induced by insulin resistance are crucial in cardiac function impairment, SGLT2i cardioprotective mechanisms against HF are several. In particular, these beneficial effects seem attributable to the significant reduction of intracellular sodium levels, well-known to exert a cardioprotective role in the prevention of oxidative stress and consequent cardiomyocyte death. From a molecular perspective, patients’ exposure to gliflozins’ treatment mimics nutrient and oxygen deprivation, with consequent autophagy stimulation. This allows to maintain the cellular homeostasis through different degradative pathways. Thus, since their introduction in the clinical practice, the hypotheses on SGLT2i mechanisms of action have changed: from simple glycosuric drugs, with consequent glucose lowering, erythropoiesis enhancing and ketogenesis stimulating, to intracellular sodium-lowering molecules. This provides their consequent cardioprotective effect, which justifies its significant reduction in CV events, especially in populations at higher risk. Finally, the updated clinical evidence of SGLT2i benefits on HF was summarized. Thus, this review aimed to analyze the cardioprotective mechanisms of sodium glucose transporter 2 inhibitors (SGLT2i) in patients with HF, as well as their clinical impact on cardiovascular events.

Activity-mediated accumulation of potassium induces a switch in firing pattern and neuronal excitability type.

During normal neuronal activity, ionic concentration gradients across a neuron's membrane are often assumed to be stable. Prolonged spiking activity, however, can reduce transmembrane gradients and affect voltage dynamics. Based on mathematical modeling, we investigated the impact of neuronal activity on ionic concentrations and, consequently, the dynamics of action potential generation. We find that intense spiking activity on the order of a second suffices to induce changes in ionic reversal potentials and to consistently induce a switch from a regular to an intermittent firing mode. This transition is caused by a qualitative alteration in the system's voltage dynamics, mathematically corresponding to a co-dimension-two bifurcation from a saddle-node on invariant cycle (SNIC) to a homoclinic orbit bifurcation (HOM). Our electrophysiological recordings in mouse cortical pyramidal neurons confirm the changes in action potential dynamics predicted by the models: (i) activity-dependent increases in intracellular sodium concentration directly reduce action potential amplitudes, an effect typically attributed solely to sodium channel inactivation; (ii) extracellular potassium accumulation switches action potential generation from tonic firing to intermittently interrupted output. Thus, individual neurons may respond very differently to the same input stimuli, depending on their recent patterns of activity and/or the current brain-state.

EXPERIMENTAL SETUP FOR EVALUATING THE TRANSPORT FUNCTIONS OF LIVING CORNEAL ENDOTHELIAL CELLS

The paper summarizes the requirements and describes an experimental setup that allows us to study the dynamics of the concentration of intracellular sodium in the endothelium of the cornea.

The role of salt-inducible kinases on the modulation of renal and intestinal Na+,K+-ATPase activity during short- and long-term high-salt intake

Type 1 salt-inducible kinases (SIK1) has been shown to act as a mediator during the cellular adaptation to variations in intracellular sodium in a variety of cell types. Type 2 SIK (SIK2) modulates various biological functions and acts as a signal transmitter in various pathways. To evaluate the role of both SIK isoforms in renal and intestinal Na+,K+-ATPase (NKA) activity, we made use of constitutive sik1−/− (SIK1–KO), sik2−/− (SIK2–KO), double sik1−/−sik2−/− (double SIK1*2-KO) knockout and wild-type (WT) mice challenged to a standard (0.3% NaCl) or chronic high-salt (HS, 8% NaCl) diet intake for 48 h or 12 weeks.Long-term HS intake in WT was accompanied by 2-fold increase in jejunal NKA activity and slight (~30% reduction) decreases in NKA in the ileum and cecum; none of these changes was accompanied by changes in the expression of α1-NKA. The ablation of SIK1 and SIK2 prevented the marked increase in jejunal NKA activity following the long-term HS intake. The ablation of SIK1 and SIK2 in mice on a long-term HS intake impacted differently in the ileum and cecum. The most interesting finding is that in SIK2–KO mice marked reductions in NKA activity were observed in the ileum and cecum when compared to WT mice, both on normal and long-term HS intake.In summary, SIK1 or SIK2 ablation on chronic high-salt intake is accompanied by modulation of NKA along the intestinal tract, which differ from those after an acute high-salt intake, and this may represent an absorptive compensatory mechanism to keep electrolyte homeostasis.

The Cardenolide Glycoside Acovenoside A Interferes with Epidermal Growth Factor Receptor Trafficking in Non-Small Cell Lung Cancer Cells.

Cardenolide glycosides are natural compounds known to inhibit the ion pumping function of the Na+/K+-ATPase in cellular systems. Interestingly, various cancer cell types are highly susceptible to cardenolide glycosides. Herein, we explore the cardenolide glycoside Acovenoside A (AcoA) with respect to its influences on human A549 non-small cell lung cancer (NSCLC) cells. We found that exposure to AcoA, digoxin and ouabain increases intracellular sodium and ATP levels indicating that the ion pumping function of the transmembrane Na+/K+-ATPase is effectively inhibited. Like digoxin and ouabain, AcoA inhibits transcription factor NF-κB activation and induces apoptotic cell death in NSCLC cells. This was confirmed by a preclinical in vivo model in which AcoA treatment of NSCLC xenografts grown on chick chorioallantoic membranes inhibited the expression of proliferation antigen Ki-67 and induced apoptotic DNA strand breaks. We aimed to elucidate the underlying mechanisms. The Na+/K+-ATPase transmembrane complex contains Src kinase and epidermal growth factor receptor (EGFR). Indeed, we found that AcoA activates Src kinase in A549 cells, but not in a cell-free assay using recombinant Src kinase. Src kinase is a downstream target of EGFR, and correlation analysis using the NCI60 database pointed to a role of EGFR in cardenolide glycoside-induced cancer cell death. Accordingly, NSCLC cells expressing hyperphosphorylated EGFRmut exhibited resistance to AcoA. To investigate the interaction between cardenolide glycosides and EGFR in detail, we performed immunoblotting studies: Whereas ligand binding and EGFR phosphorylation were not significantly affected, ubiquitinated EGFR accumulated after prolonged incubation with AcoA. To visualize EGFR trafficking we used A549 cells transfected with a fluorescent biosensor which binds to activated EGFR. Pretreatment with AcoA and digoxin induced accumulation of EGFR in endosomal compartments thus inhibiting EGF-induced EGFR degradation comparable to the Na+ ionophore monensin, a known inducer of EGFR endosomal arrest. Intracellular Na+ concentrations regulate EGFR trafficking and signaling. Na+ homeostasis is maintained by the Na+/K+-ATPase, which might account for its close interaction with the EGFR. Cardenolide glycosides inhibit the ATP-dependent Na+/K+ exchange through the Na+/K+-ATPase resulting in higher intracellular Na+ levels. Our data provide first evidence that this impedes efficient EGFR trafficking at the endosomal compartment.

Fast–Slow Variable Dissection with Two Slow Variables: A Case Study on Bifurcations Underlying Bursting for Seizure and Spreading Depression

The identification of nonlinear dynamics of bursting patterns related to multiple time scales and pathology of brain tissues is still an open problem. In the present paper, representative cases of bursting related to seizure (SZ) and spreading depression (SD) simulated in a theoretical model are analyzed. When the fast–slow variable dissection method with only one slow variable (extracellular potassium concentration, [Formula: see text]) taken as the bifurcation parameter of the fast subsystem is used, the mismatch between bifurcation points of the fast subsystem and the beginning and ending phases of burst appears. To overcome this problem, both slow variables [Formula: see text] and [Formula: see text] (intracellular sodium concentration) are regarded as bifurcation parameters of the fast subsystem, which exhibits three codimension-2 bifurcation points and multiple codimension-1 bifurcation curves containing the saddle-node bifurcation on an invariant cycle (SNIC), the supercritical Hopf bifurcation (the border between spiking and the depolarization block), and the saddle homoclinic (HC) bifurcation. The bursting patterns for SD are related to the Hopf bifurcation and the depolarization block while for SZ to SNIC. Furthermore, at the intersection points between the bursting trajectory and the bifurcation curves in plane ([Formula: see text], [Formula: see text]), the initial or termination phases of burst match the SNIC or HC point well or the Hopf point to a certain extent due to the slow passage effect, showing that the fast–slow variable dissection method with suitable process is still effective to analyze bursting activities. The results present the complex bifurcations underlying the bursting patterns and a proper performing process for the fast–slow variable dissection with two slow variables, which are helpful for modulation to bursting patterns related to brain disfunction.

Anti-VEGF therapy prevents M\xfcller intracellular edema by decreasing VEGF-A in diabetic retinopathy

BackgroundAlthough vascular endothelial growth factor A (VEGF-A) is known to play a key role in causing retinal edema, whether and how VEGF-A induces intracellular edema in the retina still remains unclear.MethodsSprague-Dawley rats were rendered diabetic with intraperitoneal injection of streptozotocin. Intravitreal injection of ranibizumab was performed 8 weeks after diabetes onset. rMC-1 cells (rat Müller cell line) were treated with glyoxal for 24 h with or without ranibizumab. The expression levels of inwardly rectifying K+ channel 4.1 (Kir4.1), aquaporin 4 (AQP4), Dystrophin 71 (Dp71), VEGF-A, glutamine synthetase (GS) and sodium-potassium-ATPase (Na+-K+-ATPase) were examined using Western blot. VEGF-A in the supernatant of the cell culture was detected with ELISA. The intracellular potassium and sodium levels were detected with specific indicators.ResultsCompared with normal control, protein expressions of Kir4.1 and AQP4 were down-regulated significantly in diabetic rat retinas, which were prevented by ranibizumab. The above changes were recapitulated in vitro. Similarly, the intracellular potassium level in glyoxal-treated rMC-1 cells was increased, while the intracellular sodium level and Na+-K+-ATPase protein level remained unchanged, compared with control. However, ranibizumab treatment decreased intracellular sodium, but not potassium.ConclusionRanibizumab protected Müller cells from diabetic intracellular edema through the up-regulation of Kir4.1 and AQP4 by directly binding VEGF-A. It also caused a reduction in intracellular osmotic pressure.

Hydrogen peroxide (H2O2) mediated activation of mTORC2 increases intracellular Na+ concentration in the renal medullary thick ascending limb of Henle

Hydrogen peroxide (H2O2) production in the renal outer medulla is an important determinant of renal medullary blood flow and blood pressure (BP) salt-sensitivity in Dahl salt-sensitive (SS) rats. The mechanisms and pathways responsible for these actions are poorly understood. Recently, we have discovered that the mTOR complex 2 (mTORC2) plays a critical role in BP salt-sensitivity of SS rats by regulating Na+ homeostasis. PP242, an inhibitor of mTORC1/2 pathways exhibits potent natriuretic actions and completely prevented salt-induced hypertension in SS rats. In the present study, we have found that chronic infusion of H2O2 into the single remaining kidney of Sprague Dawley (SD) rats (3 days) stimulated the functional marker (pAKTSer473/AKT) of mTORC2 activity measured by Western Blot analysis. No changes in mTORC1 activity in OM were observed as determined by pS6Ser235/236/S6. Using fluorescent microscopy and the Na+ sensitive dye Sodium Green, we have shown that H2O2 (100 µM added in the bath) increased intracellular sodium concentration ([Na+]i) in renal medullary thick ascending limbs (mTALs) isolated from SD rats. These responses were almost completely abolished by pretreatment of mTAL with 10 µM PP242, indicating that mTORC1/2 pathways were involved in the H2O2 induced increase of [Na+]i. mTAL cell volume remained unchanged (± 1%) by H2O2 as determined by 3D reconstruction confocal laser scanning microscopy techniques. Consistent with the microscopy data, Western Blot analysis of proteins obtained from freshly isolated mTAL treated with 100 µM H2O2 exhibited increased activity/phosphorylation of AKT (pAKTSer473/AKT) that was inhibited by PP242. This was associated with increased protein activity of the apical membrane cotransporter Na+-K+-2Cl− (NKCC2) and the Na/H exchanger (NHE-3). Na+-K+-ATPase activity was increased as reflected an increase in the ratio of pNa+-K+-ATPaseSer16 to total Na+-K+-ATPase. Overall, the results indicate that H2O2 mediated activation of mTORC2 plays a key role in transducing the observed increases of cytosolic [Na+]i despite associated increases of basolateral pump activity.

Sodium sensitivity of KNa channels in mouse CA1 neurons.

Potassium channels play an important role regulating transmembrane electrical activity in essentially all cell types. We were especially interested in those that determine the intrinsic electrical properties of mammalian central neurons. Over 30 different potassium channels have been molecularly identified in brain neurons, but there often is not a clear distinction between molecular structure and the function of a particular channel in the cell. Using patch-clamp methods to search for single potassium channels in excised inside-out (ISO) somatic patches with symmetrical potassium, we found that nearly all patches contained non-voltage-inactivating channels with a single-channel conductance of 100-200 pS. This conductance range is consistent with the family of sodium-activated potassium channels (Slo2.1, Slo2.2, or collectively, KNa). The activity of these channels was positively correlated with a low cytoplasmic Na+ concentration (2-20 mM). Cell-attached recordings from intact neurons, however, showed little or no activity of this K+ channel. Attempts to increase channel activity by increasing intracellular sodium concentration ([Na+]i) with bursts of action potentials or direct perfusion of Na+ through a whole cell pipette had little effect on KNa channel activity. Furthermore, excised outside-out (OSO) patches across a range of intracellular [Na+] showed less channel activity than we had seen with excised ISO patches. Blocking the Na+/K+ pump with ouabain increased the activity of the KNa channels in excised OSO patches to levels comparable with ISO-excised patches. Our results suggest that despite their apparent high levels of expression, the activity of somatic KNa channels is tightly regulated by the activity of the Na+/K+ pump.NEW & NOTEWORTHY We studied KNa channels in mouse hippocampal CA1 neurons. Excised inside-out patches showed the channels to be prevalent and active in most patches in the presence of Na+. Cell-attached recordings from intact neurons, however, showed little channel activity. Increasing cytoplasmic sodium in intact cells showed a small effect on channel activity compared with that seen in inside-out excised patches. Blockade of the Na+/K+ pump with ouabain, however, restored the activity of the channels to that seen in inside-out patches.

Antagonistic modulation of SIK1 and SIK2 isoforms in high blood pressure and cardiac hypertrophy triggered by high-salt intake

ABSTRACT Salt-inducible kinases (SIKs) represent a subfamily of AMPK family kinases. SIK1 has been shown to act as a mediator during the cellular adaptation to variations in intracellular sodium in a variety of cell types. SIK2, as an isoform of the SIK family, modulates various biological functions and acts as a signal transmitter in various pathways. To evaluate the role of both SIK1 and SIK2 isoforms in blood pressure (BP), body fluid regulation and cardiac hypertrophy development, we made use of constitutive sik1-/- (SIK1-KO), sik2-/- (SIK2-KO), double sik1-/-sik2-/- (double SIK1*2-KO) knockout and wild-type (WT) mice challenged to a standard (0.3% NaCl) or chronic high-salt (HS, 8% NaCl) diet intake for 12 weeks. Mice, under a standard diet intake, had similar and normal BP. On a chronic HS intake, SIK1-KO and double SIK1*2-KO mice showed increased BP, but not WT and SIK2-KO mice. A chronic HS intake led to the development of cardiac left ventricle hypertrophy (LVH) in normotensive WT and hypertensive SIK1-KO mice, but not in SIK2-KO mice. Double SIK1*2-KO mice under standard diet intake show normal BP but an increased LV mass. Remarkably, in response to a dietary stress condition, there is an increase in BP but LVH remained unchanged in double SIK1*2-KO mice. In summary, SIK1 isoform is required for maintaining normal BP in response to HS intake. LVH triggered by HS intake requires SIK2 isoform and is independent of high BP.

Multinuclear MRI to disentangle intracellular sodium concentration and extracellular volume fraction in breast cancer

The purpose of this work was to develop a novel method to disentangle the intra- and extracellular components of the total sodium concentration (TSC) in breast cancer from a combination of proton (^{1}H) and sodium (^{23}hbox {Na}) magnetic resonance imaging (MRI) measurements. To do so, TSC is expressed as function of the intracellular sodium concentration (hbox {C}_{text {IC}}), extracellular volume fraction (ECV) and the water fraction (WF) based on a three-compartment model of the tissue. TSC is measured from ^{23}hbox {Na} MRI, ECV is calculated from baseline and post-contrast ^{1}H hbox {T}_{{1}} maps, while WF is measured with a ^{1}H chemical shift technique. hbox {C}_{text {IC}} is then extrapolated from the model. Proof-of-concept was demonstrated in three healthy subjects and two patients with triple negative breast cancer. In both patients, TSC was two to threefold higher in the tumor than in normal tissue. This alteration mainly resulted from increased hbox {C}_{text {IC}} (sim 30 mM), which was sim 130% greater than in healthy conditions (10–15 mM) while the ECV was within the expected range of physiological values (0.2–0.25). Multinuclear MRI shows promise for disentangling hbox {C}_{text {IC}} and ECV by taking advantage of complementary ^{1}H and ^{23}hbox {Na} measurements.

Mitochondrial Antioxidant SkQ1 Improves Hypothermic Preservation of the Cornea.

Diseases of the cornea are a frequent cause of blindness worldwide. Keratoplasty is an efficient method for treating severely damaged cornea. The functional competence of corneal endothelial cells is crucial for successful grafting, which requires improving the media for the hypothermic cornea preservation, as well as developing the methods for the evaluation of the corneal functional properties. The transport of water and ions by the corneal endothelium is important for the viability and optic properties of the cornea. We studied the impact of SkQ1 on the equilibrium sodium concentration in the endothelial cells after hypothermic preservation of pig cornea at 4°C for 1, 5, and 10 days in standard Eusol-C solution. The intracellular sodium concentration in the endothelial cells was assayed using the fluorescent dye Sodium Green; the images were analyzed with the custom-designed CytoDynamics computer program. The concentrations of sodium in the pig corneal endothelium significantly increased after 10 days of hypothermic preservation, while addition of 1.0 nM SkQ1 to the preservation medium decreased the equilibrium concentration of intracellular sodium (at 37°C). After 10 days of hypothermic preservation, the permeability of the plasma membrane for sodium decreased in the control cells, but not in the cells preserved in the presence of 1 nM SkQ1. Therefore, SkQ1 increased the ability of endothelial cells to restore the intracellular sodium concentration, which makes SkQ1 a promising agent for facilitating retention of the functional competence of endothelial cells during cold preservation.

Ion Binding to a Mammalian Sodium/Proton Exchanger Membrane Protein from Molecular Dynamics Simulations

The Na+/H+ exchangers (NHE) are a family of proteins that regulate intracellular pH, sodium levels and cell volume, and contribute to the control of the cell cycle, cell proliferation, cell migration and vesicle trafficking. However, despite their physiological importance, detailed molecular-level structural information for the NHE has been lacking. Although a number of prokaryotic structures of sodium/proton antiporters are known, it is not clear in how far the insights from these structures are applicable to the medically important mammalian homologs.