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Patients with peripheral artery disease (PAD) are at increased risk for cardiovascular events, and higher susceptibility for cardiac arrhythmias may be involved. The objectives of this double-blinded randomized controlled FLAX-PAD trial were to determine whether daily consumption of a diet supplemented with 30 g of milled flaxseed (or placebo) over 1 year by PAD patients has effects on the prevalence of cardiac arrhythmias and exercise capacity. Cardiac arrhythmias were assessed on a cardiac stress test and at rest. At baseline, the PAD patients had a high incidence of cardiac arrhythmias (48% in the flaxseed group and 32% in the placebo group). After 1 year, the presence of cardiac arrhythmias in the flaxseed group decreased by 2% and increased by 12% in the placebo group (P > 0.05). Electrocardiographic variables (P, PR, QRS, QT, and QTc) did not change in either group during the trial. Patients from both groups improved initial and absolute claudication distances but the intergroup difference was also not statistically significant. In summary, the prevalence of cardiac arrhythmias and physical capacity trended in a positive direction for patients ingesting flaxseed but either a larger sample size or a longer intervention with flaxseed may be required to show statistically significant differences. Key words: diet, cardiovascular disease, peripheral arterial disease, claudication, atherosclerosis, heart disease, arrhythmia, exercise. Les patients presentant une maladie arterielle peripherique (ou PAD pour<< peripheral artery disease >>) sont exposes a un risque accru d'evenements cardiovasculaires, avec la possibilite d'une augmentation de la susceptibilite aux arythmies cardiaques. Cet essai FLAX-PAD controle a double insu et avec repartition aleatoire avait pour but d'etablir si, chez des patients presentant une PAD, l'administration quotidienne sur un an d'un regime alimentaire supplemente de graines de lin (ou FLAX pour<< flaxseed >>) moulues, a raison de 30 g par jour (ou d'un placebo) a des effets sur la prevalence des arythmies cardiaques et la capacite a l'exercice physique. Nous avons evalue les arythmies cardiaques a l'aide d'une epreuve d'effort et au repos. Au debut de l'etude, nous observions que les arythmies cardiaques etaient plus frequentes avec une PAD (48 % dans le groupe FLAX et 32 % avec le placebo). Apres un an, la presence d'arythmies cardiaques diminuait de 2 % dans le groupe FLAX, alors qu'elle augmentait de 12 % avec le placebo (P > 0,05). Les variables electrocardiographiques (P, PR, QRS, QT et QTc) n'ont varie dans aucun des deux groupes pendant l'essai. Nous avons observe une amelioration sur le plan des distances de claudication initiale et absolue dans les deux groupes, mais la difference entre les groupes n'etait pas statistiquement significative non plus. En resume, la prevalence des arythmies cardiaques et la capacite a l'exercice physique montraient une tendance vers l'amelioration chez les patients prenant des graines de lin, mais une augmentation de la taille de l'echantillon ou de la duree de l'administration de graines de lin pourraient etre necessaires en vue de presenter des differences significatives sur le plan statistique. [Traduit par la Redaction] Mots-cles : regime, maladie cardiovasculaire, maladie arterielle peripherique, claudication, atherosclerose, maladie cardiaque, athearythmie, exercice., Introduction Peripheral arterial disease (PAD) is a disease of limited circulation in the peripheral regions of the body, primarily the legs. PAD symptoms include painful cramping of the leg or [...]

The search for new nontraditional targets is a high priority in antibiotic design today. Bacterial membrane energetics based on sodium ion circulation offers potential alternative targets. The present work identifies the [Na.sup.+]-translocating NADH: ubiquinone oxidoreductase ([Na.sup.+]-NQR), a key respiratory enzyme in many microbial pathogens, as indispensible for the Chlamydia trachomatis infectious process. Infection by Chlamydia trachomatis significantly increased first H+ and then [Na.sup.+] levels within the host mammalian cell. A newly designed furanone [Na.sup.+]-NQR inhibitor, PEG-2S, blocked the changes in both [H.sup.+] and [Na.sup.+] levels induced by Chlamydia trachomatis infection. It also inhibited intracellular proliferation of Chlamydia trachomatis with a half-minimal inhibitory concentration in the submicromolar range but did not affect the viability of mammalian cells or bacterial species representing benign intestinal microflora. At low nanomolar concentrations ([IC.sub.50] value = 1.76 nmol/L), PEG-2S inhibited the [Na.sup.+]-NQR activity in sub-bacterial membrane vesicles isolated from Vibrio cholerae. Taken together, these results show, for the first time, that [Na.sup.+]-NQR is critical for the bacterial infectious process and is susceptible to a precisely targeted bactericidal compound in situ. The obtained data have immediate relevance for many different diseases caused by pathogenic bacteria that rely on [Na.sup.+]-NQR activity for growth, including sexually transmitted, pulmonary, oral, gum, and ocular infections. Key words: [Na.sup.+]-translocating NADH:ubiquinone oxidoreductase, [Na.sup.+]-NQR, antibiotic design, Chlamydia, bacteria, infection. La recherche de nouvelles cibles non traditionnelles est aujourd'hui une grande priorite du domaine de la conception d'antibiotiques. Les proprietes energetiques des membranes bacteriennes fondees sur le transfert des ions sodiques offrent d'autres choix de cibles potentielles. Les presents travaux traitent de la NADH : ubiquinone oxydoreductase induisant la translocation des ions [Na.sup.+] ([Na.sup.+]-NQR), une enzyme cle de la respiration cellulaire chez beaucoup de microbes pathogenes, comme element indispensable du processus infectieux associe Chlamydia trachomatis. L'infection par Chlamydia trachomatis entrainait une augmentation marquee des taux d'ions H+ puis d'ions [Na.sup.+] l'interieur des cellules de mammifere hotes. Le PEG-2S, une furanone inhibitrice de la [Na.sup.+]-NQR nouvellement concue, inhibait la variation des taux d'ions H+ comme d'ions [Na.sup.+] induite par l'infection par Chlamydia trachomatis. Il inhibait aussi la proliferation intracellulaire de Chlamydia trachomatis avec une concentration minimale inhibitrice 50 de l'ordre du submicromolaire, mais il n'affectait pas la viabilite des cellules de mammifere ni d'especes bacteriennes representant la flore microbienne intestinale benigne. A des concentrations nanomolaires faibles ([CI.sub.50] = 1,76 nmol/L), le PEG-2S inhibait l'activite de la [Na.sup.+]-NQR dans les vesicules bacteriennes submembrannaires isolees de Vibrio cholerae. Dans l'ensemble, ces resultats montrent pour la premiere fois que la [Na.sup.+]-NQR est un facteur essentiel au processus infectieux bacterien et qu'in situ, elle est sensible une substance bactericide ciblee specifiquement. Les donnees obtenues sont d'une pertinence immediate dans le cas de beaucoup de differentes maladies causees par des bacteries pathogenes qui dependent de l'activite de la [Na.sup.+]-NQR pour croitre, dont des infections pulmonaires, oculaires et transmissibles sexuellement ainsi que de la bouche et des gencives. [Traduit par la Redaction] Mots-cles : NADH : ubiquinone oxydoreductase induisant la translocation des ions [Na.sup.+], [Na.sup.+]-NQR, conception d'antibiotiques, Chlamydia, bacterie, infection., Introduction Despite the increasing incidence of antibiotic resistance today, the number of new antibiotics grows at a distressingly slow rate (Russell 2002). The essential part of the problem is that [...]

The [Na.sup.+]/[Ca.sup.2+] exchanger (NCX) is proposed to be an important protein in the regulation of [Ca.sup.2+] movements in the heart. This [Ca.sup.2+] regulatory action is thought to modulate contractile activity in the heart under normal physiological conditions and may contribute to the Ca2 + overload that occurs during ischemic reperfusion challenge. To evaluate these hypotheses, adult rat cardiomyocytes were exposed to an adenovirus that codes for short hairpin RNA (shRNA) targeting NCX gene expression through RNA interference. An adenovirus transcribing a short RNA with a scrambled nucleotide sequence was compared with the NCX-shRNA nucleotide sequence and used as a control. Freshly isolated rat cardiomyocytes were infected with virus for 48 h before examination. Cardiomyocytes maintained their characteristic morphological appearance during this short time period after isolation. NCX expression was inhibited by up to ~60% by the shRNA treatment as determined by Western blot analysis. The depletion in NCX protein was accompanied by a significant depression of NCX activity in shRNA-treated cells. [Ca.sup.2+] homeostasis was unaltered in the shRNA-treated cells upon electrical stimulation compared with control cells. However, when cardiomyocytes were exposed to a simulated ischemic solution, NCX-depleted cells were significantly protected from the rise in cytoplasmic [Ca.sup.2+] and damage that was detected in control cells during ischemia and reperfusion. Our data support the role for NCX in ischemic injury to the heart and demonstrate the usefulness of altering gene expression with an adenoviral-delivery system of shRNA in adult cardiomyocytes. short hairpin ribonucleic acid doi: 10.1152/ajpheart.00932.2009

The [Na.sup.+]/[Ca.sup.2+] exchanger (NCX) NCX1 exhibits tissue-specific alternative splicing. Such NCX splice variants as NCX1.1 and NCX1.3 are also differentially regulated by [Na.sup.+] and [Ca.sup.2+], although the physiological implications of these regulatory characteristics are unclear. On the basis of their distinct regulatory profiles, we hypothesized that cells expressing these different splice variants might exhibit unique responses to conditions promoting [Ca.sup.2+] overload, such as during exposure to cardiac glycosides or simulated ischemia. NCX1.1 or NCX1.3 was expressed in human embryonic kidney (HEK)-293 cells or rat neonatal ventricular cardiomyocytes (NVC), and expression was confirmed by Western blotting and immunocytochemical analyses. HEK-293 cells lacked NCX1 protein before transfection. With use of adenoviral vectors, neonatal cardiomyocytes were induced to overexpress the NCX1.1 splice variant by nearly twofold, whereas the NCX1.3 isoform was expressed on the endogenous NCX1.1 background. Total expression was comparable for NCX1.1 and NCX1.3. Exposure of NVC to ouabain induced a significant increase in cellular [Ca.sup.2+], an effect that was exaggerated in cells overexpressing NCX1.1, but not NCX1.3. The increase in intracellular [Ca.sup.2+] was inhibited by 5 [micro]M KB-R7943. Cardiomyocytes overexpressing NCX1.1 also exhibited a greater accumulation of intracellular [Ca.sup.2+] in response to simulated ischemia than did cells expressing NCX1.3. Similar responses were observed in HEK-293 cells where NCX1.1 was expressed. We conclude that expression of the NCX1.3 splice variant protects against severe [Ca.sup.2+] overload, whereas NCX1.1 promotes [Ca.sup.2+] overload in response to cardiac glycosides and ischemic challenges. These results highlight the importance of ionic regulation in controlling NCX1 activity under conditions that promote [Ca.sup.2+] overload. NCX1.1; NCX1.3; ouabain; ischemia

Myocardial ischemia-reperfusion activates the [Na.sup.+]/[H.sup.+] exchanger, which induces arrhythmias, cell damage, and eventually cell death. Inhibition of the exchanger reduces cell damage and lowers the incidence of arrhythmias after ischemia-reperfusion. The [omega]-3 polyunsaturated fatty acids (PUFAs) are also known to be cardioprotective and antiarrhythmic during ischemia-reperfusion challenge. Some of the action of PUFAs may occur via inhibition of the [Na.sup.+]/[H.sup.+] exchanger. The purpose of our study was to determine the capacity for selected PUFAs to alter cardiac sarcolemmal (SL) [Na.sup.+]/[H.sup.+] exchange. Cardiac membranes highly enriched in SL vesicles were exposed to 10-100 [micro]M eicosapentanoic acid (EPA) or docosahexanoic acid (DHA). [H.sup.+]-dependent [sup.22][Na.sup.+] uptake was inhibited by 30-50% after treatment with [greater than or equal to] 50 [micro]M EPA or [greater than or equal to] 25 [micro]M DHA. This was a specific effect of these PUFAs, because 50 [micro]M linoleic acid or linolenic acid had no significant effect on [Na.sup.+]/[H.sup.+] exchange. The SL vesicles did not exhibit an increase in passive [Na.sup.+] efflux after PUFA treatment. In conclusion, EPA and DHA can potently inhibit cardiac SL [Na.sup.+]/[H.sup.+] exchange at physiologically relevant concentrations. This may explain, in part, their known cardioprotective effects and antiarrhythmic actions during ischemia-reperfusion. ischemia-reperfusion; myocardial cell death; antiarrhythmic; eicosapentanoic acid; docosahexanoic acid

The relationship between myocardial dysfunction and sodium-hydrogen ion exchange in during reperfusion was assessed through studies monitoring reaction of coronary-perfused right ventricular wall to delayed exposure to dimethyl amiloride (DMA). Results have shown that the extravascular accumulation of the drug was time dependent and crucial for the drug to effectuate cardioprotection. Activation of Na+/H+ exchange was critical for reperfusion.

A study was performed to determine heart responses of JCR/LA-corpulent rats (JCR-LA-cp) to an interval of ischemic insult. JCR/LA-cp rat is a distinguished genetic animal strain with similar characteristics of the type II diabetes in humans. It was believed that JCR-LA-cp hearts have improper regulation of intracellular calcium concentration. Results of the study showed enhanced sensitivity of murine hearts to ischemia-reperfusion injury as the rats grew older. The significance of results was correlated to the type of diabetes to be considered in myocardial dysfunction.

The potential of amiloride and their analogues in protecting the right ventricular wall from postischemic contractile dysfunction is attributed to the blockage of Na+-H+ exchanger. The events pertaining to the migration of Ca2+ into the myocardium resulting in cellular dysfunction, damage and necrosis is avoided by preventing the Na+ ions entry. The amiloride derivatives 5- N,N-hexamethylene-amiloride (HMA) and ethylisopropyl amiloride (EIPA) are 10 times more efficient in preventing Na+-H+ exchange than 5- N,N-dimethyl-amiloride (DMA).

Myocardial ischemia-reperfusion (I/R) injury increases the generation of oxidized phosphatidylcholines (OxPCs), which results in cell death. However, the mechanism by which OxPCs mediate cell death and cardiac dysfunction is largely unknown. The aim of this study was to determine the mechanisms by which OxPC triggers cardiomyocyte cell death during reperfusion injury. Adult rat ventricular cardiomyocytes were treated with increasing concentrations of various purified fragmented OxPCs. Cardiomyocyte viability, bioenergetic response, and calcium transients were determined in the presence of OxPCs. Five different fragmented OxPCs resulted in a decrease in cell viability, with 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC) and 1-palmitoyl-2-(9'-oxo-nonanoyl)- sn-glycero-3-phosphocholine (PONPC) having the most potent cardiotoxic effect in both a concentration and time dependent manner (P < 0.05). POVPC and PONPC also caused a significant decrease in Ca2+ transients and net contraction in isolated cardiomyocytes compared to vehicle treated control cells (P < 0.05). PONPC depressed maximal respiration rate (P < 0.01; 54%) and spare respiratory capacity (P < 0.01; 54.5%). Notably, neither caspase 3 activation or TUNEL staining was observed in cells treated with either POVPC or PONPC. Further, cardiac myocytes treated with OxPCs were indistinguishable from vehicle-treated control cells with respect to nuclear high-mobility group box protein 1 (HMGBP1) activity. However, glutathione peroxidase 4 activity was markedly suppressed in cardiomyocytes treated with POVPC and PONPC coincident with increased ferroptosis. Importantly, cell death induced by OxPCs could be suppressed by E06 Ab, directed against OxPCs or by ferrostatin-1, which bound the sn-2 aldehyde of POVPC during I/R. The findings of the present study demonstrate that oxidation of phosphatidylcholines during I/R generate bioactive phospholipid intermediates that disrupt mitochondrial bioenergetics and calcium transients and provoke wide spread cell death through ferroptosis. Neutralization of OxPC with E06 or with ferrostatin-1 prevents cell death during reperfusion. Our study demonstrates a novel signaling pathway that operationally links generation of OxPC during cardiac I/R to ferroptosis. Interventions designed to target OxPCs may prove beneficial in mitigating ferroptosis during I/R injury in individuals with ischemic heart disease. [ABSTRACT FROM AUTHOR]

The omega-3 fatty acid, alpha linolenic acid (ALA) found in plant-derived foods induces significant cardiovascular benefits when ingested. ALA may be cardioprotective during ischemia; however, the mechanism(s) responsible for this effect is unknown. Isolated adult rat cardiomyocytes were exposed to medium containing ALA for 24 h and then exposed to non-ischemic (control), simulated ischemia (ISCH), or simulated ischemia/reperfusion (IR) conditions. Cardiomyocyte phospholipids were extracted and analyzed by an HPLC/electrospray ionization tandem mass spectrometry system. Pre-treatment of cells with ALA resulted in a significant incorporation of ALA within cardiomyocyte phosphatidylcholine. Cell death, DNA fragmentation and caspase-3 activity increased during ischemia and ischemia/reperfusion. Two pro-apoptotic oxidized phosphatidylcholine (OxPC) species, 1-palmitoyl-2-(5′-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC), and 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC) were significantly increased during both ischemia and ischemia/reperfusion. Pre-treatment of the cells with ALA resulted in a significant reduction in cell death during ischemia and ischemia/reperfusion challenge. Apoptosis was also inhibited during ischemia and ischemia/reperfusion as shown by reduced DNA fragmentation and decreased caspase activation. ALA pre-treatment significantly decreased the production of POVPC and PGPC during ischemia and ischemia/reperfusion. ALA pre-treatment also significantly increased in resting Ca during ischemia or ischemia/reperfusion but did not improve Ca transients. ALA protects the cardiomyocyte from apoptotic cell death during simulated ISCH and IR by inhibiting the production of specific pro-apoptotic OxPC species. OxPCs represent a viable interventional target to protect the heart during ischemic challenge. [ABSTRACT FROM AUTHOR]

The comprehensive characterization of low-flow ischemia and reperfusion in single adult cardiomyocytes was studied to determine whether it is important to control contractile activity. Throughout ischemia and during reperfusion, cardiomyocytes were stimulated with control perfusate. The results showed that many of the responses observed in whole hearts can be reproduced by an ischemia-mimetic solution administered to single, isolated adult cardiomyocytes.

The Na+/Ca2+ exchanger (NCX) is proposed to be an important protein in the regulation of Ca2+ movements in the heart. This Ca2+ regulatory action is thought to modulate contractile activity in the heart under normal physiological conditions and may contribute to the Ca2+ overload that occurs during ischemic reperfusion challenge. To evaluate these hypotheses, adult rat cardiomyocytes were exposed to an adenovirus that codes for short hairpin RNA (shRNA) targeting NCX gene expression through RNA interference. An adenovirus transcribing a short RNA with a scrambled nucleotide sequence was compared with the NCX-shRNA nucleotide sequence and used as a control. Freshly isolated rat cardiomyocytes were infected with virus for 48 h before examination. Cardiomyocytes maintained their characteristic morphological appearance during this short time period after isolation. NCX expression was inhibited by up to ∼60% by the shRNA treatment as determined by Western blot analysis. The depletion in NCX protein was accompanied by a significant depression of NCX activity in shRNA-treated cells. Ca2+ homeostasis was unaltered in the shRNA-treated cells upon electrical stimulation compared with control cells. However, when cardiomyocytes were exposed to a simulated ischemic solution, NCX-depleted cells were significantly protected from the rise in cytoplasmic Ca2+ and damage that was detected in control cells during ischemia and reperfusion. Our data support the role for NCX in ischemic injury to the heart and demonstrate the usefulness of altering gene expression with an adenoviral-delivery system of shRNA in adult cardiomyocytes. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Dietary intake of ω-3 polyunsaturated fatty acids (PUFA) like α-linolenic acid (ALA) is antiarrhythmic and cardioprotective. PUFA may also be beneficial in hypertension. Altered Na+–Ca2+ exchanger (NCX) activity has been implicated in arrhythmias, hypertension and heart failure and may be a target for PUFA. Thus, we tested the effects of ALA and other distinct fatty acids on the cardiac (NCX1.1) and vascular (NCX1.3) NCX isoforms. Methods: HEK293 cells stably expressing NCX isoforms were ramped from +60 to −100 mV (over 1600 ms) in the absence and presence of 25 μM oleic acid (OA, ω-9), linoleic acid (LA, ω-6), ALA (ω-3), or eicosapentaenoic acid (EPA, ω-3). NiCl2 (5 mM) was used to inhibit and therefore identify the NCX current. The effect of 25 μM ALA on NCX1.1 and NCX1.3 activity was also assessed in adult rat ventricular cardiomyocytes and rabbit aortic vascular smooth muscle cells (VSMC) by measuring [Ca2+]i following substitution of [Na+]o with Li+. Results: Application of Ni2+ had no effect in non-transfected cells. ALA and EPA (25 μM) reduced the Ni2+-sensitive forward NCX1.1 current (at −100 mV) by 64% and reverse current (at +60 mV) by 57%, and inhibited the Ni2+-sensitive NCX1.3 forward and reverse currents by 79% and 76%, respectively. Neither OA nor LA (25 μM) affected the NCX1.1 currents, but both partially inhibited the forward and reverse mode NCX1.3 currents. Inhibition of NCX1.3 by ALA occurred at a much lower IC50 (∼19 nM) than for NCX1.1 (∼120 nM). In cardiomyocytes and VSMC, ALA significantly reduced the Li+-induced rise in intracellular [Ca2+]. Conclusions: NCX1.3 is more sensitive to inhibition by ALA than NCX1.1. In addition, only ω-3 PUFA inhibits NCX1.1, but several classes of fatty acids inhibit NCX1.3. The differential sensitivity of NCX isoforms to fatty acids may have important implications as therapeutic approaches for hypertension, heart failure and arrhythmias. [Copyright &y& Elsevier]

The Na+/Ca2+ exchanger (NCX) NCX1 exhibits tissue-specific alternative splicing. Such NCX splice variants as NCX1.1 and NCX1.3 are also differentially regulated by Na+ and Ca2+, although the physiological implications of these regulatory characteristics are unclear. On the basis of their distinct regulatory profiles, we hypothesized that cells expressing these different splice variants might exhibit unique responses to conditions promoting Ca2+ overload, such as during exposure to cardiac glycosides or simulated ischemia. NCX1.1 or NCX1.3 was expressed in human embryonic kidney (HEK)-293 cells or rat neonatal ventricular cardiomyocytes (NVC), and expression was confirmed by Western blotting and immunocytochemical analyses. HEK-293 cells lacked NCX1 protein before transfection. With use of adenoviral vectors, neonatal cardiomyocytes were induced to overexpress the NCX1.1 splice variant by nearly twofold, whereas the NCX1.3 isoform was expressed on the endogenous NCX1.1 background. Total expression was comparable for NCX1.1 and NCX1.3. Exposure of NVC to ouabain induced a significant increase in cellular Ca2+ an effect that was exaggerated in cells overexpressing NCX1.1, but not NCX1.3. The increase in intracellular Ca2+ was inhibited by 5 μM KB-R7943. Cardiomyocytes overexpressing NCX1.1 also exhibited a greater accumulation of intracellular Ca2+ in response to simulated ischemia than did cells expressing NCX1.3. Similar responses were observed in HEK-293 cells where NCX1.1 was expressed. We conclude that expression of the NCX1.3 splice variant protects against severe Ca2+ overload, whereas NCX1.1 promotes Ca2+ overload in response to cardiac glycosides and ischemic challenges. These results highlight the importance of ionic regulation in controlling NCX1 activity under conditions that promote Ca2+ overload. [ABSTRACT FROM AUTHOR]

Determines the capacity of selected Polyunsaturated Fatty (PUFA) acids to alter cardiac Sarcolemmal (SL) exchange. Enrichment of cardiac membranes in SL vesicles; Stability of SL vesicles in passive Na&sup+; efflux after PUFA treatment; Cardioprotective effects and antirrhythmic actions during ischemia-reperfusion.

Objective: The aim was to examine the regulation of the cardiac Na+/H+ exchanger NHE-1 isoform mRNA in response to ischaemia and acidosis in the mammalian myocardium. Methods: Male Sprague Dawley rat hearts were perfused in a non-circulated retrograde fashion according to the Langendorff method. Hearts were perfused for 3 h at flow rates of either 10 ml·min−1 (control), or 3, 1, or 0 ml·min−1 (ischaemia) followed by 5 min of reperfusion. Hearts were immediately frozen in liquid N2, and stored at −80 °C until ready for RNA isolation. Northern blot analysis was used to examine expression of the NHE-1 isoform of the Na+/H+ exchanger message in these isolated perfused hearts. Activity of the Na+/H+ exchanger was assessed in primary cultures of neonatal rat myocytes under either control conditions or after treatment with chronic, low external pH. Results: A decrease in developed tension and an increase in resting tension was observed which was dependent upon the severity of the ischaemic episode. Low flow ischaemia of 3 ml·min−1 caused increased Na+/H+ exchanger message levels, while perfusion at more reduced flow rates eliminated the increase. Treatment of primary cultures of isolated myocytes with low external pH resulted in increased ability to recover from an acute acid load. Conclusions: Low flow ischaemia can increase the Na+/H+ exchanger message in the intact mammalian myocardium. More severe ischaemia prevents the increase, suggesting that severely damaged tissue may not be capable of the ischaemic response. Primary cultures of isolated myocytes can respond to chronic low external pH by increasing Na+/H+ exchanger activity. [ABSTRACT FROM PUBLISHER]