Increase In Intracellular Na Research Articles

Simultaneous Increases in Intracellular Sodium and Tonicity Boost Antimicrobial Activity of Macrophages.

Inflamed and infected tissues can display increased local sodium (Na+) levels, which can have various effects on immune cells. In macrophages, high salt (HS) leads to a Na+/Ca2+-exchanger 1 (NCX1)-dependent increase in intracellular Na+ levels. This results in augmented osmoprotective signaling and enhanced proinflammatory activation, such as enhanced expression of type 2 nitric oxide synthase and antimicrobial function. In this study, the role of elevated intracellular Na+ levels in macrophages was investigated. Therefore, the Na+/K+-ATPase (NKA) was pharmacologically inhibited with two cardiac glycosides (CGs), ouabain (OUA) and digoxin (DIG), to raise intracellular Na+ without increasing extracellular Na+ levels. Exposure to HS conditions and treatment with both inhibitors resulted in intracellular Na+ accumulation and subsequent phosphorylation of p38/MAPK. The CGs had different effects on intracellular Ca2+ and K+ compared to HS stimulation. Moreover, the osmoprotective transcription factor nuclear factor of activated T cells 5 (NFAT5) was not upregulated on RNA and protein levels upon OUA and DIG treatment. Accordingly, OUA and DIG did not boost nitric oxide (NO) production and showed heterogeneous effects toward eliminating intracellular bacteria. While HS environments cause hypertonic stress and ionic perturbations, cardiac glycosides only induce the latter. Cotreatment of macrophages with OUA and non-ionic osmolyte mannitol (MAN) partially mimicked the HS-boosted antimicrobial macrophage activity. These findings suggest that intracellular Na+ accumulation and hypertonic stress are required but not sufficient to mimic boosted macrophage function induced by increased extracellular sodium availability.

Activation of TRPV4 channels promotes the loss of cellular ATP in organotypic slices of the mouse neocortex exposed to chemical ischemia.

The vertebrate brain has an exceptionally high energy need. During ischemia, intracellular ATP concentrations decline rapidly, resulting in the breakdown of ion gradients and cellular damage. Here, we employed the nanosensor ATeam1.03YEMK to analyse the pathways driving the loss of ATP upon transient metabolic inhibition in neurons and astrocytes of the mouse neocortex. We demonstrate that brief chemical ischemia, induced by combined inhibition of glycolysis and oxidative phosphorylation, results in a transient decrease in intracellular ATP. Neurons experienced a larger relative decline and showed less ability to recover from prolonged (>5min) metabolic inhibition than astrocytes. Blocking voltage-gated Na+ channels or NMDA receptors ameliorated the ATP decline in neurons and astrocytes, while blocking glutamate uptake aggravated the overall reduction in neuronal ATP, confirming the central role of excitatory neuronal activity in the cellular energy loss. Unexpectedly, pharmacological inhibition of transient receptor potential vanilloid 4 (TRPV4) channels significantly reduced the ischemia-induced decline in ATP in both cell types. Imaging with Na+ -sensitive indicator dye ING-2 furthermore showed that TRPV4 inhibition also reduced ischemia-induced increases in intracellular Na+ . Altogether, our results demonstrate that neurons exhibit a higher vulnerability to brief metabolic inhibition than astrocytes. Moreover, they reveal an unexpected strong contribution of TRPV4 channels to the loss of cellular ATP and suggest that the demonstrated TRPV4-related ATP consumption is most likely a direct consequence of Na+ influx. Activation of TRPV4 channels thus provides a hitherto unacknowledged contribution to the cellular energy loss during energy failure, generating a significant metabolic cost in ischemic conditions. KEY POINTS: In the ischemic brain, cellular ATP concentrations decline rapidly, which results in the collapse of ion gradients and promotes cellular damage and death. We analysed the pathways driving the loss of ATP upon transient metabolic inhibition in neurons and astrocytes of the mouse neocortex. Our results confirm the central role of excitatory neuronal activity in the cellular energy loss and demonstrate that neurons experience a larger decline in ATP and are more vulnerable to brief metabolic stress than astrocytes. Our study also reveals a new, previously unknown involvement of osmotically activated transient receptor potential vanilloid 4 (TRPV4) channels to the reduction in cellular ATP in both cell types and indicates that this is a consequence of TRPV4-mediated Na+ influx. We conclude that activation of TRPV4 channels provides a considerable contribution to the cellular energy loss, thereby generating a significant metabolic cost in ischemic conditions.

Abstract 2312: Efficacy of targeted osmotic lysis is increased by cell cycle inhibition in M Phase

Abstract Voltage-gated sodium channels (VGSCs) are upregulated in aggressive carcinomas, making these channels a target for novel clinical therapies. Targeted Osmotic Lysis (TOL) is a novel cancer therapy that combines pharmacologically blocking Na+,K+, ATPase (sodium pumps) while stimulating VGSCs with a pulsed electric field. The consequent increase in intracellular Na+ causes an osmotic lysis of the cells that overexpress VGSCs. Noncancerous cells, with fewer VGSCs do not lyse. We hypothesized that variability in efficacy of TOL is due to VGSC expression that varies across the cell cycle. We assessed cell surface expression of VGSCs and Na+,K+-ATPase during phases of the cell cycle in which there are single copies of DNA compared with phases in which DNA has doubled. For this, DNA was labeled with either propidium iodide or DAPI and VGSCs were labeled with a pan-specific VGSC antibody while Na+,K+-ATPases were labelled with a pan-specific Na+,K+-ATPase antibody in eight immortalized cancer and non-cancer cell lines. With flow cytometry we showed that VGSC expression doubled during phases of cell division (S-M phases) while Na+,K+-ATPase expression increased by 1.5-fold. To further elucidate the role of VGSCs and Na+,K+-ATPases throughout the cell cycle, S-Trityl-L-cysteine (STLC) was used to suspend the cell cycle in M phase. We hypothesized that treating cancer cells with TOL in the S-M phases would lead to increased cell death, compared to cells that were not suspended in M phase by STLC (G0-G1 phases). Cells were either treated with STLC or media without drug for 24 hours, then exposed to TOL treatment. The efficacy of the treatment was measured using a MTT assay revealing that cell death was greater in STLC-treated cells than control cells. By using cell cycle inhibitors, we may increase the efficacy of TOL for treating advanced carcinomas that overexpress VGSCs. Citation Format: Samantha Edenfield, Harry J. Gould, Dennis Paul. Efficacy of targeted osmotic lysis is increased by cell cycle inhibition in M Phase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2312.

Dividing Cells are Most Susceptible to Targeted Osmotic Lysis Cancer Therapy

Voltage‐gated sodium channels (VGSCs) are upregulated in aggressive carcinomas, making these channels a target for novel clinical therapies. Targeted Osmotic Lysis (TOL) is a novel cancer therapy that combines pharmacologically blocking Na+,K+, ATPase (sodium pumps) while stimulating VGSCs with a pulsed electric field. The consequent increase in intracellular Na+ causes an osmotic lysis of the cells that overexpress VGSCs. Noncancerous cells, with fewer VGSCs do not lyse. We hypothesized that variability in efficacy of TOL is due to VGSC expression that varies across the cell cycle. We assessed cell surface expression of VGSCs and Na+,K+‐ATPase during phases of the cell cycle in which there are single copies of DNA compared with phases in which DNA has doubled. For this, DNA was labeled with either propidium iodide (PI) or DAPI and VGSCs were labeled with a pan‐specific VGSC antibody while Na+,K+‐ATPases were labelled with a pan‐specific Na+,K+‐ATPase antibody in eight immortalized cancer and non‐cancer cell lines. With flow cytometry we showed that VGSC expression doubled during phases of cell division (S‐M phases) compared to G0‐G1 phases, whereas Na+,K+‐ATPase expression increased by 1.5‐fold. To investigate whether cells in S‐M phases are more susceptible to TOL due to the increase in VGSCs, cells were treated and immediately fixed and stained with PI for cell cycle analysis. There was a 30% decrease in the percentage of total cells that were treated with TOL compared to cells that did not receive TOL treatment. This finding is evidence that dividing cells are more susceptible to TOL than cells in G0‐G1 phases. It is thus likely that combined therapies will likely lead to better patient outcomes.

Effect of adenosine triphosphate, benidipine and their combinations on bevacizumab-induced kidney damage in rats.

Bevacizumab-induced vascular endothelial growth factor (VEGF) inhibition may lead to a decrease in adenosine triphosphate (ATP) levels, an increase in intracellular Na+ and Ca2+ concentrations and an increase in reactive oxygen species (ROS) generation, as well as to cell damage. To investigate the biochemical and histopathological effects of ATP, benidipine and ATP in combination with benidipine on bevacizumab-induced kidney damage in rats. Rats were divided into 5 treatment groups: bevacizumab (BVZ) alone, ATP + bevacizumab (ABVZ), benidipine + bevacizumab (BBVZ), ATP + benidipine + bevacizumab (ABBVZ), and healthy controls (HC). Adenosine triphosphate (25 mg/kg), benidipine (4 mg/kg orally), ATP (25 mg/kg) + benidipine (4 mg/kg), or saline were administered to albino Wistar rats. One hour after treatment, bevacizumab was injected at a dose of 10 mg/kg to induce kidney damage. Two doses of bevacizumab were delivered 15 days apart. Adenosine triphosphate + benidipine were administered once a day for 1 month. Malondialdehyde (MDA), total oxidant status (TOS), creatinine, and blood urea nitrogen (BUN) levels of the BVZ, BBVZ, ABVZ, ABBVZ, and HC groups were ranked from highest to lowest. Conversely, total glutathione (tGSH) and total antioxidant status (TAS) kidney tissue values were ranked from lowest to highest, respectively. Hemorrhage, tubular necrosis and grade 3 focal tubular atrophy were observed in the BVZ group. Atrophy and grade 2 necrosis were observed in the BBVZ group and atrophy and grade 1 necrosis were observed in the ABVZ group. Only grade 1 atrophy was observed in the ABBVZ group. Adenosine triphosphate reduced bevacizumab-induced renal toxicity significantly more effectively than benidipine. However, the combination of ATP + benidipine further reduced bevacizumab-induced renal toxicity relative to benidipine or ATP alone. These data indicate that ATP + benidipine might be a potential therapeutic strategy for the prevention of bevacizumab-induced renal toxicity.

Electrophysiological Effects of Ionophore-induced Increases in Intracellular Na+ in Cardiomyocytes

Na ionophores increase intracellular Na+ ([Na+]i). Membrane potentials and currents were measured using microelectrode and whole-cell patch-clamp techniques. Monensin (10-6-3×10-5 M) reduced the slope of the pacemaker potentials and shortened the action potential duration (APD) in sino-atrial nodal and Purkinje cells. Monensin (10-5 M) shortened the APD and reduced the amplitude of the plateau phase in ventricular myocytes. Monensin decreased the hyperpolarization-activated inward current (If), and it increased the transient outward potassium current (Ito) in Purkinje cells. In addition, monensin decreased the sodium current (INa), shifting the inactivation curve to the hyperpolarized direction. Moreover, monensin decreased the L-type calcium current (ICa) in ventricular myocytes. The Na+-Ca2+ exchange current (INa-Ca) was augmented particularly in the reverse mode, and the Na+-K+ pump current (INa-K) was also activated by monensin in cardiomyocytes. The ATP-activated potassium current (IK,ATP) could be induced by monensin. Notably, the inward rectifying K+ current (IK1), and the slow delayed outward K+ current (IKs) were not affected evidently by monensin. Collectively, alteration of [Na+]i can influence the activities of various ion channels and transporters. Thus, the significance of altered [Na+]i should be taken into consideration in the action of drugs affecting [Na+]i such as digitalis, Na+ channel blockers, and Na+ channel activating agents.

Abstract P70: SPAK/OSR1 Signaling as a Novel Target for Post-Stroke Oxidative Stress Brain Injury

Stroke is the second leading cause of death worldwide, and ischemic stroke accounts for the vast majority of stroke cases. Currently, recombinant tissue plasminogen activator and endovascular thrombectomy are the two primary therapy strategies for acute ischemic stroke patients. Reactive oxygen species (ROS)-mediated oxidative stress can cause brain injury during reperfusion. We have shown that the Ste20/SPS1-related proline-alanine-rich protein kinase/oxidative stress-responsive kinase-1 (SPAK/OSR1) are activated in ischemic stroke brains, resulting in worsened outcomes in murine stroke models. SPAK activation induces the production of pro-inflammatory cytokines. Post-stroke administration of a novel SPAK inhibitor ZT-1a attenuates cerebral edema and protects against brain damage in in vivo model of ischemic stroke. However, whether ROS mediated oxidative stress directly activate SPAK/OSR1 pathway and induces SPAK pro-inflammatory cytokine production in ischemic brains remains unknown. In our extended study, we examined activation of SPAK/OSR1 and its substrate Na-K-Cl cotransporter (NKCC1) in cultured mouse primary neurons in response to hydrogen peroxide (H 2 O 2 )-mediated oxidative stress. We found that exposure of neurons to H 2 O 2 for 24 hrs triggered upregulation of protein expression and phosphorylation activation of SPAK/OSR1 and NKCC1 ( p < 0.05), which are accompanied with an increase in intracellular Na + concentration and neuronal death ( p < 0.01). These changes were blocked by an ROS scavenger ebselen. Interestingly, both novel SPAK inhibitor ZT-1a and NKCC1 inhibitor bumetanide are able to block H 2 O 2 -induced neuronal damage. We are in the process to assess effects of SPAK inhibitor ZT-1a in reducing ROS-mediated inflammation and brain injury in in vivo model of ischemic stroke. Together, our study suggests that ROS can activate SPAK/OSR1 complex during reperfusion injury and the therapeutic potentials of SPAK inhibitor ZT-1a for ischemic stroke.

Monensin-Induced Increase in Intracellular Na+ Induces Changes in Na+ and Ca2+ Currents and Regulates Na+-K+ and Na+-Ca2+ Transport in Cardiomyocytes

Background/Aims: Monensin, an Na ionophore, increases intracellular Na ([Na]i). Alteration of [Na]i influences ion transport through the sarcolemmal membrane. So far, the effects of monensin on ventricular myocytes have not been examined in detail. The main objective of this study was to elucidate the mechanism via which monensin-evoked increases in [Na]i affect the membrane potential and currents in ventricular myocytes of guinea pigs. Methods: Membrane potentials and currents were measured using the whole-cell patch-clamp technique in single myocytes. The concentration of intracellular Ca ([Ca]i) was evaluated by measuring fluorescence intensity of Fluo-4. Results: Monensin (10⁻⁵M) shortened the action potential duration (APD) and reduced the amplitude of the plateau phase. In addition, monensin decreased the sodium current (I_Na) and shifted the inactivation curve to the hyperpolarized direction. Moreover, it decreased the L-type calcium current (I_Ca). However, this effect was attenuated by increasing the buffering capacity of [Ca]i. The Na-Ca exchange current (I_Na-Ca) was activated particularly in the reverse mode. Na-K pump current (I_Na-K) was also activated. Notably, the inward rectifying K current (I_K1) was not affected, and the change in the delayed outward K current (I_K) was not evident. Conclusion: These results suggest that the monensin-induced shortened APD and reduced amplitude of the plateau phase are primarily due to the decrease in the I_Ca, the activation of the reverse mode of I_Na-Ca, and the increased I_Na-K, and second due to the decreased I_Na. The I_K and the I_K1 may not be associated with the abovementioned changes induced by monensin. The elevation of [Na]i can exert multiple influences on electrophysiological phenomena in cardiac myocytes.

Sodium Fluctuations in Astroglia and Their Potential Impact on Astrocyte Function.

Astrocytes are the main cell type responsible for the regulation of brain homeostasis, including the maintenance of ion gradients and neurotransmitter clearance. These processes are tightly coupled to changes in the intracellular sodium (Na+) concentration. While activation of the sodium-potassium-ATPase (NKA) in response to an elevation of extracellular K+ may decrease intracellular Na+, the cotransport of transmitters, such as glutamate, together with Na+ results in an increase in astrocytic Na+. This increase in intracellular Na+ can modulate, for instance, metabolic downstream pathways. Thereby, astrocytes are capable to react on a fast time scale to surrounding neuronal activity via intracellular Na+ fluctuations and adjust energy production to the demand of their environment. Beside the well-documented conventional roles of Na+ signaling mainly mediated through changes in its electrochemical gradient, several recent studies have identified more atypical roles for Na+, including protein interactions leading to changes in their biochemical activity or Na+-dependent regulation of gene expression. In this review, we will address both the conventional as well as the atypical functions of astrocytic Na+ signaling, presenting the role of transporters and channels involved and their implications for physiological processes in the central nervous system (CNS). We will also discuss how these important functions are affected under pathological conditions, including stroke and migraine. We postulate that Na+ is an essential player not only in the maintenance of homeostatic processes but also as a messenger for the fast communication between neurons and astrocytes, adjusting the functional properties of various cellular interaction partners to the needs of the surrounding network.

Modulation of the cardiac Na+-Ca2+ exchanger by cytoplasmic protons: Molecular mechanisms and physiological implications

A precise temporal and spatial control of intracellular Ca2+ concentration is essential for a coordinated contraction of the heart. Following contraction, cardiac cells need to rapidly remove intracellular Ca2+ to allow for relaxation. This task is performed by two transporters: the plasma membrane Na+-Ca2+ exchanger (NCX) and the sarcoplasmic reticulum (SR) Ca2+‐ATPase (SERCA). NCX extrudes Ca2+ from the cell, balancing the Ca2+entering the cytoplasm during systole through L-type Ca2+ channels. In parallel, following SR Ca2+ release, SERCA activity replenishes the SR, reuptaking Ca2+ from the cytoplasm.The activity of the mammalian exchanger is fine-tuned by numerous ionic allosteric regulatory mechanisms. Micromolar concentrations of cytoplasmic Ca2+ potentiate NCX activity, while an increase in intracellular Na+ levels inhibits NCX via a mechanism known as Na+-dependent inactivation. Protons are also powerful inhibitors of NCX activity. By regulating NCX activity, Ca2+, Na+ and H+ couple cell metabolism to Ca2+ homeostasis and therefore cardiac contractility. This review summarizes the recent progress towards the understanding of the molecular mechanisms underlying the ionic regulation of the cardiac NCX with special emphasis on pH modulation and its physiological impact on the heart.

Relation between activity-induced intracellular sodium transients and ATP dynamics in mouse hippocampal neurons.

Employing quantitative Na+ -imaging and Förster resonance energy transfer-based imaging with ATeam1.03YEMK (ATeam), we studied the relation between activity-induced Na+ influx and intracellular ATP in CA1 pyramidal neurons of the mouse hippocampus. Calibration of ATeam in situ enabled a quantitative estimate of changes in intracellular ATP concentrations. Different paradigms of stimulation that induced global Na+ influx into the entire neuron resulted in decreases in [ATP] in the range of 0.1-0.6mm in somata and dendrites, while Na+ influx that was locally restricted to parts of dendrites did not evoke a detectable change in dendritic [ATP]. Our data suggest that global Na+ transients require global cellular activation of the Na+ /K+ -ATPase resulting in a consumption of ATP that transiently overrides its production. For recovery from locally restricted Na+ influx, ATP production as well as fast intracellular diffusion of ATP and Na+ might prevent a local drop in [ATP]. Excitatory neuronal activity results in the influx of Na+ through voltage- and ligand-gated channels. Recovery from accompanying increases in intracellular Na+ concentrations ([Na+ ]i ) is mainly mediated by the Na+ /K+ -ATPase (NKA) and is one of the major energy-consuming processes in the brain. Here, we analysed the relation between different patterns of activity-induced [Na+ ]i signalling and ATP in mouse hippocampal CA1 pyramidal neurons by Na+ imaging with sodium-binding benzofurane isophthalate (SBFI) and employing the genetically encoded nanosensor ATeam1.03YEMK (ATeam). In situ calibrations demonstrated a sigmoidal dependence of the ATeam Förster resonance energy transfer ratio on the intracellular ATP concentration ([ATP]i ) with an apparent KD of 2.6mm, indicating its suitability for [ATP]i measurement. Induction of recurrent network activity resulted in global [Na+ ]i oscillations with amplitudes of ∼10mm, encompassing somata and dendrites. These were accompanied by a steady decline in [ATP]i by 0.3-0.4mm in both compartments. Global [Na+ ]i transients, induced by afferent fibre stimulation or bath application of glutamate, caused delayed, transient decreases in [ATP]i as well. Brief focal glutamate application that evoked transient local Na+ influx into a dendrite, however, did not result in a measurable reduction in [ATP]i . Our results suggest that ATP consumption by the NKA following global [Na+ ]i transients temporarily overrides its availability, causing a decrease in [ATP]i . Locally restricted Na+ transients, however, do not result in detectable changes in local [ATP]i , suggesting that ATP production, together with rapid intracellular diffusion of both ATP and Na+ from and to unstimulated neighbouring regions, counteracts a local energy shortage under these conditions.

Salt Inducible Kinase Signaling Networks: Implications for Acute Kidney Injury and Therapeutic Potential.

A number of signal transduction pathways are activated during Acute Kidney Injury (AKI). Of particular interest is the Salt Inducible Kinase (SIK) signaling network, and its effects on the Renal Proximal Tubule (RPT), one of the primary targets of injury in AKI. The SIK1 network is activated in the RPT following an increase in intracellular Na+ (Na+in), resulting in an increase in Na,K-ATPase activity, in addition to the phosphorylation of Class IIa Histone Deacetylases (HDACs). In addition, activated SIKs repress transcriptional regulation mediated by the interaction between cAMP Regulatory Element Binding Protein (CREB) and CREB Regulated Transcriptional Coactivators (CRTCs). Through their transcriptional effects, members of the SIK family regulate a number of metabolic processes, including such cellular processes regulated during AKI as fatty acid metabolism and mitochondrial biogenesis. SIKs are involved in regulating a number of other cellular events which occur during AKI, including apoptosis, the Epithelial to Mesenchymal Transition (EMT), and cell division. Recently, the different SIK kinase isoforms have emerged as promising drug targets, more than 20 new SIK2 inhibitors and activators having been identified by MALDI-TOF screening assays. Their implementation in the future should prove to be important in such renal disease states as AKI.

Erythrocyte ion content and dehydration modulate maximal Gardos channel activity in KCNN4 V282M/+ hereditary xerocytosis red cells.

Hereditary xerocytosis (HX) is caused by missense mutations in either the mechanosensitive cation channel PIEZO1 or the Ca2+-activated K+ channel KCNN4. All HX-associated KCNN4 mutants studied to date have revealed increased current magnitude and red cell dehydration. Baseline KCNN4 activity was increased in HX red cells heterozygous for KCNN4 mutant V282M. However, HX red cells maximally stimulated by Ca2+ ionophore A23187 or by PMCA Ca2+-ATPase inhibitor orthovanadate displayed paradoxically reduced KCNN4 activity. This reduced Ca2+-stimulated mutant KCNN4 activity in HX red cells was associated with unchanged sensitivity to KCNN4 inhibitor senicapoc and KCNN4 activator Ca2+, with slightly elevated Ca2+ uptake and reduced PMCA activity, and with decreased KCNN4 activation by calpain inhibitor PD150606. The altered intracellular monovalent cation content of HX red cells prompted experimental nystatin manipulation of red cell Na and K contents. Nystatin-mediated reduction of intracellular K+ with corresponding increase in intracellular Na+ in wild-type cells to mimic conditions of HX greatly suppressed vanadate-stimulated and A23187-stimulated KCNN4 activity in those wild-type cells. However, conferral of wild-type cation contents on HX red cells failed to restore wild-type-stimulated KCNN4 activity to those HX cells. The phenotype of reduced, maximally stimulated KCNN4 activity was shared by HX erythrocytes expressing heterozygous PIEZO1 mutants R2488Q and V598M, but not by HX erythrocytes expressing heterozygous KCNN4 mutant R352H or PIEZO1 mutant R2456H. Our data suggest that chronic KCNN4-driven red cell dehydration and intracellular cation imbalance can lead to reduced KCNN4 activity in HX and wild-type red cells.

Targeted Osmotic Lysis of H28 Mesothelioma Cells

Mesothelioma is an aggressive cancer of the pleura cells of the chest cavity commonly linked to asbestos exposure. With a post‐diagnosis prognosis of between 6 and 12 months. Traditional chemotherapy increases survival time by only 11 weeks. Targeted Osmotic Lysis (TOL) is a novel cancer therapeutic that exploits cancer cells' upregulation of Voltage‐Gated Sodium Channels (VGSC) by pairing a pharmacological blocker of Na+, K+‐ATPase (sodium pumps), such as digoxin or ouabain, with electric or magnetic stimulation of VGSCs. The increase in intracellular Na+ causes an osmotic lysis of cells that over‐express VGSCs. TOL has been shown to selectively lyse highly invasive breast cancer cells, such as MDA‐MB 231, while leaving the normal tissue intact. To test the hypothesis that TOL would be an effective treatment for mesothelioma, we incubated H28 mesothelioma cells or MeT‐5A normal pleural effusion cells in 0–500 nM digoxin for 10 min, then activated the VGSCs with a 0–5 VDC electric current for 30 min. Using video microscopy, lysis was assessed by two independent observers with cytosolic extrusion as the measure. TOL effectively lysed H28 cells dose‐ and stimulus‐dependently, with a maximum cell death of 94.2% Less than 5% of cells in the Drug only, Stimulation only, and Non‐treated groups died (p<.0001). MeT‐5A cells did not lyse. Likewise, when we used a pulsed magnetic field (90 mT, 25 pps) to stimulate VGSCs, H28 cells lysed dose‐ and stimulation‐dependently, whereas control treatments and Met‐5a cells did not. Together these results are evidence that TOL causes significant cell death in mesothelioma cells compared to the normal cells. Thus, TOL may be an effective treatment for mesothelioma.Support or Funding InformationThis research was supported by a grant from Oleander Medical TechnologiesThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract 062: Renal Hydrogen Peroxide Prevents Salt-Sensitive Hypertension

C57Bl/6 and BALB/c are different in the sensitivity of their blood pressure (BP) to NaCl. High NaCl diet increases BP in C57Bl/6J but not BALB/c mice. However, C57Bl/6J mice are less prone to hypertension-induced renal injury than other mouse strains. The goal of this study was to determine the role of H 2 O 2 in salt-sensitive hypertension. Basal renal levels of reactive oxygen species, including H 2 O 2, were higher in BALB/c renal proximal tubule cells (RPTC-BALB/c) than RPTCs from C57Bl/6J mice (RPTC-C57Bl/6J) (60.8 ± 5 % vs 41.8 ± 12 %, n=8, P<0.03). Incubation media with 170 mM NaCl (HS) increased H 2 O 2 production in RPTC-BALB/c but not in RPTC-C57Bl/6J, compared with RPTCs incubated in low (90 mM) or normal (145 mM) NaCl (+68±43%, 90 vs 170 mM, n=7, P<0.05). H 2 O 2 (10 μM) treatment of the basolateral side of RPTC-BALB/c in Transwells increased intracellular Na + 1.62-fold that of vehicle-treated cells (n=4, P<0.05). Over-expression of catalase, abrogated the H 2 O 2 -induced increase in intracellular Na + in RPTC-BALB/c. Over-expression of catalase in the kidneys of BALB/c mice on normal (0.9%) NaCl diet did not alter their SBP. However, on high (4%) NaCl diet, SBP was increased in catalase over-expressing mice, relative to vehicle-treated controls (98±1.1 vs 112±1.4 mm Hg, n=3, P<0.05). Decreasing H 2 O 2 by overexpression of catalase predisposes BALB/c mice to salt-sensitive hypertension, suggesting that high salt-induced H 2 O 2 negatively regulates renal sodium transport and provides resistance to salt-induced hypertension.

Hydrogen Peroxide Increases Intracellular Sodium Concentration in the Medullary Thick Ascending Limb Isolated from Sprague‐Dawley Rats

Elevations of renal medullary hydrogen peroxide (H2O2) produce a salt‐sensitive form of hypertension as shown by chronic infusion of H2O2 into the renal medulla of a single remaining kidney of normotensive Sprague‐Dawley (SD) rats (Makino et al., Hypertension, 2003) and salt‐resistant consomic SS.13BN rats. Conversely, chronic medullary infusion of catalase (H2O2 scavenger) into the renal medulla of Dahl salt‐sensitive rats significantly reduced salt induced hypertension (Taylor and Cowley, Am J Physiol Regul Integr Comp Physiol, 2005). The goal of this study was to assess the effects of H2O2 upon intracellular sodium concentration [Na+]i and the role of mTORC1 and mTORC2 signaling in the medullary thick ascending limb (mTAL) isolated from the outer medulla (OM) of SD rats.Methodsrats were anesthetized, the kidney flushed with saline, removed, and mTALs dissected from the inner stripe of the OM at 4°C under a stereomicroscope. The mTALs were attached to poly‐Lysine coated cover slips and incubated with HBSS containing 10 nM of the Na+‐sensitive fluorescence dye NaGreen and 0.05% Pluronic acid F‐127 for 30 min at room temperature. The mTALs were washed and then placed in a heated chamber (37°C) mounted on the stage of an inverted Nikon TE‐2000U microscope for recording.ResultsIt was found that 100 uM H2O2 resulted in a significant increase in [Na+]i (p<0.05). The responses to pretreatment of mTAL with 10 uM PP242 (mTORC1/2 inhibitor), 200 nM rapamycin (mTORC1 specific inhibitor), or 1 mM furosemide (Na+/K+/2Cl− inhibitor) were then studied. We found that each of these inhibitors nearly abolished H2O2 induced increases in intracellular Na+. Western blot analysis of isolated mTAL from SD rats for each of the treatments found that 100 uM H2O2 increased the activation of AKT (pAKTSer473; a surrogate for mTORC1/2 activation) and S6 (pS6Ser235/236; a surrogate for mTORC1 activation) and were inhibited by their respective inhibitors.ConclusionTogether these observations indicate that H2O2 acts through the mTOR signaling pathways to inhibit NKCC2 activity, which would in turn be expected to lead to sodium retention and hypertension.Support or Funding InformationHL 122662This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Computational flow cytometry reveals that cryopreservation induces spermptosis but subpopulations of spermatozoa may experience capacitation-like changes.

The reduced lifespan of cryopreserved spermatozoa in the mare reproductive tract has been attributed to both capacitative and apoptotic changes. However, there is a lack of studies investigating both phenomena simultaneously. In order to improve our knowledge in this particular point, we studied in raw and frozen-thawed samples apoptotic and capacitative markers using a wide battery of test based in flow cytometry. Apoptotic markers evaluated were caspase 3 activity, externalization of phosphatidylserine (PS), and mitochondrial membrane potential. Markers of changes resembling capacitation were membrane fluidity, tyrosine phosphorylation, and intracellular sodium. Conventional and computational flow cytometry using nonlinear dimensionally reduction techniques (t-distributed stochastic neighbor embedding (t-SNE)) and automatic classification of cellular expression by nonlinear stochastic embedding (ACCENSE) were used. Most of the changes induced by cryopreservation were apoptotic, with increase in caspase 3 activation (P < 0.01), PS translocation to the outer membrane (P < 0.001), loss of mitochondrial membrane potential (P < 0.05), and increase in intracellular Na+ (P < 0.01). Average values of markers of capacitative changes were not affected by cryopreservation; however, the analysis of the phenotype of individual spermatozoa using computational flow cytometry revealed the presence of subpopulations of spermatozoa experiencing capacitative changes. For the first time advanced computational techniques were applied to the analysis of spermatozoa, and these techniques were able to disclose relevant information of the ejaculate that remained hidden using conventional flow cytometry.

Na(+) -Activated K(+) Channels in Rat Supraoptic Neurones.

The magnocellular neurosecretory cells (MNCs) of the hypothalamus secrete the neurohormones vasopressin and oxytocin. The systemic release of these hormones depends on the rate and pattern of MNC firing and it is therefore important to identify the ion channels that contribute to the electrical behaviour of MNCs. In the present study, we report evidence for the presence of Na(+) -activated K(+) (KN a ) channels in rat MNCs. KN a channels mediate outwardly rectifying K(+) currents activated by the increases in intracellular Na(+) that occur during electrical activity. Although the molecular identity of native KN a channels is unclear, their biophysical properties are consistent with those of expressed Slick (slo 2.1) and Slack (slo 2.2) proteins. Using immunocytochemistry and Western blot experiments, we found that both Slick and Slack proteins are expressed in rat MNCs. Using whole cell voltage clamp techniques on acutely isolated rat MNCs, we found that inhibiting Na(+) influx by the addition of the Na(+) channel blocker tetrodotoxin or the replacement of Na(+) in the external solution with Li(+) caused a significant decrease in sustained outward currents. Furthermore, the evoked outward current density was significantly higher in rat MNCs using patch pipettes containing 60mm Na(+) than it was when patch pipettes containing 0mm Na(+) were used. Our data show that functional KN a channels are expressed in rat MNCs. These channels could contribute to the activity-dependent afterhyperpolarisations that have been identified in the MNCs and thereby play a role in the regulation of their electrical behaviour.

Na+ Influx Induced by New Antimalarials Causes Rapid Alterations in the Cholesterol Content and Morphology of Plasmodium falciparum.

Among the several new antimalarials discovered over the past decade are at least three clinical candidate drugs, each with a distinct chemical structure, that disrupt Na+ homeostasis resulting in a rapid increase in intracellular Na+ concentration ([Na+]i) within the erythrocytic stages of Plasmodium falciparum. At present, events triggered by Na+ influx that result in parasite demise are not well-understood. Here we report effects of two such drugs, a pyrazoleamide and a spiroindolone, on intraerythrocytic P. falciparum. Within minutes following the exposure to these drugs, the trophozoite stage parasite, which normally contains little cholesterol, was made permeant by cholesterol-dependent detergents, suggesting it acquired a substantial amount of the lipid. Consistently, the merozoite surface protein 1 and 2 (MSP1 and MSP2), glycosylphosphotidylinositol (GPI)-anchored proteins normally uniformly distributed in the parasite plasma membrane, coalesced into clusters. These alterations were not observed following drug treatment of P. falciparum parasites adapted to grow in a low [Na+] growth medium. Both cholesterol acquisition and MSP1 coalescence were reversible upon the removal of the drugs, implicating an active process of cholesterol exclusion from trophozoites that we hypothesize is inhibited by high [Na+]i. Electron microscopy of drug-treated trophozoites revealed substantial morphological changes normally seen at the later schizont stage including the appearance of partial inner membrane complexes, dense organelles that resemble “rhoptries” and apparent nuclear division. Together these results suggest that [Na+]i disruptor drugs by altering levels of cholesterol in the parasite, dysregulate trophozoite to schizont development and cause parasite demise.

Maduramicin Rapidly Eliminates Malaria Parasites and Potentiates the Gametocytocidal Activity of the Pyrazoleamide PA21A050.

New strategies targeting Plasmodium falciparum gametocytes, the sexual-stage parasites that are responsible for malaria transmission, are needed to eradicate this disease. Most commonly used antimalarials are ineffective against P. falciparum gametocytes, allowing patients to continue to be infectious for over a week after asexual parasite clearance. A recent screen for gametocytocidal compounds demonstrated that the carboxylic polyether ionophore maduramicin is active at low nanomolar concentrations against P. falciparum sexual stages. In this study, we showed that maduramicin has an EC50 (effective concentration that inhibits the signal by 50%) of 14.8 nM against late-stage gametocytes and significantly blocks in vivo transmission in a mouse model of malaria transmission. In contrast to other reported gametocytocidal agents, maduramicin acts rapidly in vitro, eliminating gametocytes and asexual schizonts in less than 12 h without affecting uninfected red blood cells (RBCs). Ring stage parasites are cleared by 24 h. Within an hour of drug treatment, 40% of the normally crescent-shaped gametocytes round up and become spherical. The number of round gametocytes increases to >60% by 2 h, even before a change in membrane potential as monitored by MitoProbe DiIC1 (5) is detectable. Maduramicin is not preferentially taken up by gametocyte-infected RBCs compared to uninfected RBCs, suggesting that gametocytes are more sensitive to alterations in cation concentration than RBCs. Moreover, the addition of 15.6 nM maduramicin enhanced the gametocytocidal activity of the pyrazoleamide PA21A050, which is a promising new antimalarial candidate associated with an increase in intracellular Na(+) concentration that is proposed to be due to inhibition of PfATP4, a putative Na(+) pump. These results underscore the importance of cation homeostasis in sexual as well as asexual intraerythrocytic-stage P. falciparum parasites and the potential of targeting this pathway for drug development.