scholarly journals Intermittent Hypoxia Inhibits Na+-H+ Exchange-Mediated Acid Extrusion Via Intracellular Na+ Accumulation in Cardiomyocytes

2018 ◽  
Vol 46 (3) ◽  
pp. 1252-1262 ◽  
Author(s):  
Huai-Ren Chang ◽  
Chih-Feng Lien ◽  
Jing-Ren Jeng ◽  
Jen-Che Hsieh ◽  
Chen-Wei Chang ◽  
...  
Keyword(s):  
Reperfusion Injury ◽  
Intracellular Calcium ◽  
Intracellular Ph ◽  
Recovery Rate ◽  
Intermittent Hypoxia ◽  
Ros Production ◽  
Tyrode Solution ◽  
Neonatal Cardiomyocytes ◽  
Cardioprotective Effects ◽  
Acid Extrusion

Background/Aims: Intermittent hypoxia (IH) has been shown to exert preconditioning-like cardioprotective effects. It also has been reported that IH preserves intracellular pH (pHi) during ischemia and protects cardiomyocytes against ischemic reperfusion injury. However, the exact mechanism is still unclear. Methods: In this study, we used proton indicator BCECF-AM to analyze the rate of pHi recovery from acidosis in the IH model of rat neonatal cardiomyocytes. Neonatal cardiomyocytes were first treated with repetitive hypoxia-normoxia cycles for 1-4 days. Cells were then acid loaded with NH4Cl, and the rate of pHi recovery from acidosis was measured. Results: We found that the pHi recovery rate from acidosis was much slower in the IH group than in the room air (RA) group. When we treated cardiomyocytes with Na+-H+ exchange (NHE) inhibitors (Amiloride and HOE642) or Na+-free Tyrode solution during the recovery, there was no difference between RA and IH groups. We also found intracellular Na+ concentration ([Na+]i) significantly increased after IH exposure for 4 days. However, the phenomenon could be abolished by pretreatment with ROS inhibitors (SOD and phenanathroline), intracellular calcium chelator or Na+-Ca2+ exchange (NCX) inhibitor. Furthermore, the pHi recovery rate from acidosis became faster in the IH group than in the RA group when inhibition of NCX activity. Conclusions: These results suggest that IH would induce the elevation of ROS production. ROS then activates Ca2+-efflux mode of NCX and results in intracellular Na+ accumulation. The rise of [Na+]i further inhibits the activity of NHE-mediated acid extrusion and retards the rate of pHi recovery from acidosis during IH.

scholarly journals Extracellular Cl− modulates shrinkage-induced activation of Na+/H+exchanger in rat mesangial cells

2000 ◽  
Vol 278 (6) ◽  
pp. C1218-C1229 ◽  
Author(s):  
Yukio Miyata ◽  
Shigeaki Muto ◽  
Satoru Yanagiba ◽  
Yasushi Asano
Keyword(s):  
Benzoic Acid ◽  
Intracellular Ph ◽  
Recovery Rate ◽  
Mesangial Cells ◽  
Ph Sensitive ◽  
Extrusion Rate ◽  
Wide Range ◽  
Dependent Cell ◽  
Acid Extrusion ◽  
Dependent Processes

To examine the effect of hyperosmolality on Na+/H+ exchanger (NHE) activity in mesangial cells (MCs), we used a pH-sensitive dye, 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-AM, to measure intracellular pH (pHi) in a single MC from rat glomeruli. All the experiments were performed in CO2/[Formula: see text]-free HEPES solutions. Exposure of MCs to hyperosmotic HEPES solutions (500 mosmol/kgH2O) treated with mannitol caused cell alkalinization. The hyperosmolality-induced cell alkalinization was inhibited by 100 μM ethylisopropylamiloride, a specific NHE inhibitor, and was dependent on extracellular Na+. The hyperosmolality shifted the Na+-dependent acid extrusion rate vs. pHi by 0.15–0.3 pH units in the alkaline direction. Removal of extracellular Cl− by replacement with gluconate completely abolished the rate of cell alkalinization induced by hyperosmolality and inhibited the Na+-dependent acid extrusion rate, whereas, under isosmotic conditions, it caused no effect on Na+-dependent pHi recovery rate or Na+-dependent acid extrusion rate. The Cl−-dependent cell alkalinization rate under hyperosmotic conditions was partially inhibited by pretreatment with 5-nitro-2-(3-phenylpropylamino)benzoic acid, DIDS, and colchicine. We conclude: 1) in MCs, hyperosmolality activates NHE to cause cell alkalinization, 2) the acid extrusion rate via NHE is greater under hyperosmotic conditions than under isosmotic conditions at a wide range of pHi, 3) the NHE activation under hyperosmotic conditions, but not under isosmotic conditions, requires extracellular Cl−, and 4) the Cl−-dependent NHE activation under hyperosmotic conditions partly occurs via Cl− channel and microtubule-dependent processes.

scholarly journals Intracellular pH-regulating mechanism of the squid axon. Relation between the external Na+ and HCO-3 dependences.

1985 ◽  
Vol 85 (3) ◽  
pp. 325-345 ◽  
Author(s):  
W F Boron
Keyword(s):  
Intracellular Ph ◽  
Recovery Rate ◽  
Ion Pair ◽  
Squid Axon ◽  
Extrusion Rate ◽  
Pair Model ◽  
Buffering Power ◽  
Series Of Experiments ◽  
Acid Extrusion ◽  
External Ph

The intracellular pH-regulating mechanism of the squid axon was examined for its dependence on the concentrations of external Na+ and HCO3-, always at an external pH (pHo) of 8.0. Axons having an initial intracellular pH (pHi) of approximately 7.4 were internally dialyzed with a solution of pH 6.5 that contained 400 mM Cl- and no Na+. After pHi had fallen to approximately 6.6, dialysis was halted, thereby returning control of pHi to the axon. With external Na+ and HCO-3 present, intracellular pH (pHi) increased because of the activity of the pHi-regulating system. The acid extrusion rate (i.e., equivalent efflux of H+, JH) is the product of the pHi recovery rate, intracellular buffering power, and the volume-to-surface ratio. The [HCO3-]o dependence of JH was examined at three fixed levels of [Na+]o: 425, 212, and 106 mM. In all three cases, the apparent Jmax was approximately 19 pmol X cm-2 X s-1. However, the apparent Km (HCO3-) was approximately inversely proportional to [Na+]o, rising from 2.6 to 5.4 to 9.7 mM as [Na+]o was lowered from 425 to 212 to 106 mM, respectively. The [Na+]o dependence of JH was similarly examined at three fixed levels of [HCO3-]o: 12, 6, and 3 mM. The Jmax values did not vary significantly from those in the first series of experiments. The apparent Km (Na+), however, was approximately inversely related to [HCO3-]o, rising from 71 to 174 to 261 mM as [HCO3-]o was lowered from 12 to 6 to 3 mM, respectively. These results agree with the predictions of the ion-pair model of acid extrusion, which has external Na+ and CO3= combining to form the ion pair NaCO3-, which then exchanges for internal Cl-. When the JH data are replotted as a function of [NaCO3-]o, data from all six groups of experiments fall along the same Michaelis-Menten curve, with an apparent Km (NaCO3-) of 80 microM. The ordered and random binding of Na+ and CO3= cannot be ruled out as possible models, but are restricted in allowable combinations of rate constants.

scholarly journals Hypertrophy-Reduced Autophagy Causes Cardiac Dysfunction by Directly Impacting Cardiomyocyte Contractility

Cells ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 805
Author(s):  
Christiane Ott ◽  
Tobias Jung ◽  
Sarah Brix ◽  
Cathleen John ◽  
Iris R. Betz ◽  
...  
Keyword(s):  
Cardiomyocyte Hypertrophy ◽  
Aortic Constriction ◽  
Cell Contractility ◽  
Neonatal Cardiomyocytes ◽  
Cardiomyocyte Contractility ◽  
Cardioprotective Effects ◽  
Modified Proteins ◽  
Cardiomyocyte Autophagy

Cardiac remodeling and contractile dysfunction are leading causes in hypertrophy-associated heart failure (HF), increasing with a population’s rising age. A hallmark of aged and diseased hearts is the accumulation of modified proteins caused by an impaired autophagy-lysosomal-pathway. Although, autophagy inducer rapamycin has been described to exert cardioprotective effects, it remains to be shown whether these effects can be attributed to improved cardiomyocyte autophagy and contractility. In vivo hypertrophy was induced by transverse aortic constriction (TAC), with mice receiving daily rapamycin injections beginning six weeks after surgery for four weeks. Echocardiographic analysis demonstrated TAC-induced HF and protein analyses showed abundance of modified proteins in TAC-hearts after 10 weeks, both reduced by rapamycin. In vitro, cardiomyocyte hypertrophy was mimicked by endothelin 1 (ET-1) and autophagy manipulated by silencing Atg5 in neonatal cardiomyocytes. ET-1 and siAtg5 decreased Atg5–Atg12 and LC3-II, increased natriuretic peptides, and decreased amplitude and early phase of contraction in cardiomyocytes, the latter two evaluated using ImageJ macro Myocyter recently developed by us. ET-1 further decreased cell contractility in control but not in siAtg5 cells. In conclusion, ET-1 decreased autophagy and cardiomyocyte contractility, in line with siAtg5-treated cells and the results of TAC-mice demonstrating a crucial role for autophagy in cardiomyocyte contractility and cardiac performance.

scholarly journals Mitochondrial depolarization underlies delay in permeability transition by preconditioning with isoflurane: roles of ROS and Ca2+

2010 ◽  
Vol 299 (2) ◽  
pp. C506-C515 ◽  
Author(s):  
Filip Sedlic ◽  
Ana Sepac ◽  
Danijel Pravdic ◽  
Amadou K. S. Camara ◽  
Martin Bienengraeber ◽  
...  
Keyword(s):  
Cell Survival ◽  
Mitochondrial Permeability Transition ◽  
Permeability Transition Pore ◽  
Permeability Transition ◽  
Underlying Mechanism ◽  
Ros Production ◽  
Trypan Blue Exclusion ◽  
Mptp Opening ◽  
Mitochondrial Ros ◽  
Cardioprotective Effects

During reperfusion, the interplay between excess reactive oxygen species (ROS) production, mitochondrial Ca2+ overload, and mitochondrial permeability transition pore (mPTP) opening, as the crucial mechanism of cardiomyocyte injury, remains intriguing. Here, we investigated whether an induction of a partial decrease in mitochondrial membrane potential (ΔΨm) is an underlying mechanism of protection by anesthetic-induced preconditioning (APC) with isoflurane, specifically addressing the interplay between ROS, Ca2+, and mPTP opening. The magnitude of APC-induced decrease in ΔΨm was mimicked with the protonophore 2,4-dinitrophenol (DNP), and the addition of pyruvate was used to reverse APC- and DNP-induced decrease in ΔΨm. In cardiomyocytes, ΔΨm, ROS, mPTP opening, and cytosolic and mitochondrial Ca2+ were measured using confocal microscope, and cardiomyocyte survival was assessed by Trypan blue exclusion. In isolated cardiac mitochondria, antimycin A-induced ROS production and Ca2+ uptake were determined spectrofluorometrically. In cells exposed to oxidative stress, APC and DNP increased cell survival, delayed mPTP opening, and attenuated ROS production, which was reversed by mitochondrial repolarization with pyruvate. In isolated mitochondria, depolarization by APC and DNP attenuated ROS production, but not Ca2+ uptake. However, in stressed cardiomyocytes, a similar decrease in ΔΨm attenuated both cytosolic and mitochondrial Ca2+ accumulation. In conclusion, a partial decrease in ΔΨm underlies cardioprotective effects of APC by attenuating excess ROS production, resulting in a delay in mPTP opening and an increase in cell survival. Such decrease in ΔΨm primarily attenuates mitochondrial ROS production, with consequential decrease in mitochondrial Ca2+ uptake.

scholarly journals Editor’s Choice- Reperfusion cardiac arrhythmias and their relation to reperfusion-induced cell death

2018 ◽  
Vol 8 (2) ◽  
pp. 142-152 ◽  
Author(s):  
Kirian van der Weg ◽  
Frits W Prinzen ◽  
Anton PM Gorgels
Keyword(s):  
Cell Death ◽  
Reperfusion Injury ◽  
Intracellular Calcium ◽  
Ventricular Arrhythmias ◽  
Mitochondrial Protein ◽  
Calcium Overload ◽  
Reperfusion Arrhythmias ◽  
Potential Marker ◽  
Additional Cell ◽  
Oxidative Species

Reperfusion does not only salvage ischaemic myocardium but can also cause additional cell death which is called lethal reperfusion injury. The time of reperfusion is often accompanied by ventricular arrhythmias, i.e. reperfusion arrhythmias. While both conditions are seen as separate processes, recent research has shown that reperfusion arrhythmias are related to larger infarct size. The pathophysiology of fatal reperfusion injury revolves around intracellular calcium overload and reactive oxidative species inducing apoptosis by opening of the mitochondrial protein transition pore. The pathophysiological basis for reperfusion arrhythmias is the same intracellular calcium overload as that causing fatal reperfusion injury. Therefore both conditions should not be seen as separate entities but as one and the same process resulting in two different visible effects. Reperfusion arrhythmias could therefore be seen as a potential marker for fatal reperfusion injury.

scholarly journals NHE1, NHE2, and NHE3 contribute to regulation of intracellular pH in murine duodenal epithelial cells

2000 ◽  
Vol 278 (2) ◽  
pp. G197-G206 ◽  
Author(s):  
J. Praetorius ◽  
D. Andreasen ◽  
B. L. Jensen ◽  
M. A. Ainsworth ◽  
U. G. Friis ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Western Blot ◽  
Intracellular Ph ◽  
Blot Analysis ◽  
Western Blot Analysis ◽  
Mrna Level ◽  
Rt Pcr ◽  
Acid Extrusion ◽  
Molecular Expression ◽  
Nhe Isoforms

Na+/H+-exchangers (NHE) mediate acid extrusion from duodenal epithelial cells, but the isoforms involved have not previously been determined. Thus we investigated 1) the contribution of Na+-dependent processes to acid extrusion, 2) sensitivity to Na+/H+ exchange inhibitors, and 3) molecular expression of NHE isoforms. By fluorescence spectroscopy the recovery of intracellular pH (pHi) was measured on suspensions of isolated acidified murine duodenal epithelial cells loaded with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Expression of NHE isoforms was studied by RT-PCR and Western blot analysis. Reduction of extracellular Na+ concentration ([Na+]o) during pHirecovery decreased H+ efflux to minimally 12.5% of control with a relatively high apparent Michaelis constant for extracellular Na+. The Na+/H+exchange inhibitors ethylisopropylamiloride and amiloride inhibited H+ efflux maximally by 57 and 80%, respectively. NHE1, NHE2, and NHE3 were expressed at the mRNA level (RT-PCR) as well as at the protein level (Western blot analysis). On the basis of the effects of low [Na+]o and inhibitors we propose that acid extrusion in duodenal epithelial cells involves Na+/H+ exchange by isoforms NHE1, NHE2, and NHE3.

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