The role of Na+/H+ exchanger in Ca2+ overload and ischemic myocardial damage in hearts from type 2 diabetic db/db mice.

Background: A higher increase in intracellular Na(+) via Na(+)/H(+) exchanger (NHE) during ischemia has been reported in type 2 diabetic mouse hearts. We investigated the role of NHE in inducing changes in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and alterations in ventricular function during ischemia-reperfusion in type 2 diabetic mouse hearts.

Methods: Hearts from male type 2 diabetic db/db (12-15 weeks old) and age-matched control db/+ mice were subjected to Langendorff perfusion and loaded with 4 μM of the Ca(2+) indicator fura-2.

3-(R)-[3-(2-methoxyphenylthio-2-(S)-methylpropyl]amino-3,4-dihydro-2H-1,5-benzoxathiepine bromhydrate (F 15845) prevents ischemia-induced heart remodeling by reduction of the intracellular Na+ overload.

The present study investigates whether 3-(R)-[3-(2-methoxyphenylthio-2-(S)-methylpropyl]amino-3,4-dihydro-2H-1,5-benzoxathiepine bromhydrate (F 15845), a new, persistent sodium current blocker, can reduce the ischemic Na(+) accumulation and exert short- and long-term cardioprotection after myocardial infarction. First, F 15845 concentration-dependently reduced veratrine-induced diastolic contracture (IC(50) = 0.14 microM) in isolated atria.

ERM proteins mediate the effects of Na+/H+ exchanger (NHE1) activation in cardiac myocytes.

Aims: Ezrin, radixin, and moesin (ERM) proteins have been implicated in regulating signalling molecules. The aim of the present study was to investigate the activity and subcellular distribution of ERM proteins in cardiac myocytes from both Wistar and diabetic Goto-Kakizaki (GK) rats, and the role of these proteins in mediating the downstream effects of the cardiac sarcolemmal Na+/H+ exchanger (NHE1) activation in response to cell acidification.

Methods And Results: Immunofluorescence microscopy revealed that activated ERM proteins were localized predominantly at the intercalated disc regions in left ventricular (LV) myocytes of both Wistar and GK rats under basal conditions.

Diabetes-related metabolic perturbations in cardiac myocyte.

Although the pathogenesis of diabetic cardiomyopathy is poorly understood, recent evidence implicates perturbations in cardiac energy metabolism. Whereas mitochondrial fatty acid oxidation is the chief energy source for the normal postnatal mammalian heart, the relative contribution of glucose utilization pathways is significant, allowing the plasticity necessary for steady ATP production in the context of diverse physiologic and dietary conditions. In the uncontrolled diabetic state, because of the combined effects of insulin resistance and high circulating fatty acids, cardiac myocytes use fatty acids almost exclusively to support ATP synthesis.

Enhanced activity of the myocardial Na+/H+ exchanger contributes to left ventricular hypertrophy in the Goto-Kakizaki rat model of type 2 diabetes: critical role of Akt.

Aims/hypothesis: Diabetes mellitus is a strong risk factor for the development of heart failure, and left ventricular (LV) hypertrophy has been detected in a significant proportion of diabetic patients. Because several studies have suggested that the Na(+)/H(+) exchanger (NHE1) plays a part in the molecular mechanisms involved in cardiac hypertrophy, we investigated its activity and its role in LV myocytes from the Goto-Kakizaki (GK) rat model of type 2 diabetes.

Materials And Methods: Fluorometric measurements were used to assess sarcolemmal NHE1 activity in isolated myocytes.

Intracellular sodium increase and susceptibility to ischaemia in hearts from type 2 diabetic db/db mice.

Aims/hypothesis: An important determinant of sensitivity to ischaemia is altered ion homeostasis, especially disturbances in intracellular Na(+) (Na(i)(+)) handling. As no study has so far investigated this in type 2 diabetes, we examined susceptibility to ischaemia-reperfusion in isolated hearts from diabetic db/db and control db/+ mice and determined whether and to what extent the amount of (Na(i)(+)) increase during a transient period of ischaemia could contribute to functional alterations upon reperfusion.

Methods: Isovolumic hearts were exposed to 30-min global ischaemia and then reperfused.

High glucose-induced apoptosis through store-operated calcium entry and calcineurin in human umbilical vein endothelial cells.

Diabetes mellitus causes multiple cardiovascular complications. Previous studies have shown that prolonged exposure (96 h) of human umbilical vein endothelial cells (HUVECs) to hyperglycemia causes a significant increase in apoptosis. We report here that this increase in apoptosis is associated with an increase in Ca(2+) current (whole cell patch-clamp recorded) resulting from Ca(2+) entry mediated by store-operated channels (SOCs).

Diabetic cardiomyopathy.

Although the pathogenesis of diabetic cardiomyopathy is poorly understood, recent evidence implicates perturbations in cardiac energy metabolism. Whereas mitochondrial fatty acid oxidation is the chief energy source for the normal postnatal mammalian heart, the relative contribution of glucose utilization pathways is significant, allowing the plasticity necessary for steady ATP production in the context of diverse physiologic and dietary conditions. Because of the importance of insulin in the regulation of myocardial metabolism, chronic insulin deficiency or resistance results in a marked reduction in cardiac glucose utilization such that the heart relies almost exclusively on fatty acids to generate energy.

Different pathways for sodium entry in cardiac cells during ischemia and early reperfusion.

A number of data are consistent with the hypothesis that increases in intracellular Na+ concentration (Na+i) during ischemia and early reperfusion lead to calcium overload and exacerbation of myocardial injury. However, the mechanisms underlying the increased Na+i remain unclear. 23Na nuclear magnetic resonance spectroscopy was used to monitor Na+i in isolated rat hearts perfused with a high concentration of fatty acid as can occur under some pathological conditions.

The ERK pathway regulates Na(+)-HCO(3)(-) cotransport activity in adult rat cardiomyocytes.

The sarcolemmal Na(+)-HCO cotransporter (NBC) is stimulated by intracellular acidification and acts as an acid extruder. We examined the role of the ERK pathway of the MAPK cascade as a potential mediator of NBC activation by intracellular acidification in the presence and absence of angiotensin II (ANG II) in adult rat ventricular myocytes. Intracellular pH (pH(i)) was recorded with the use of seminaphthorhodafluor-1.

Anti-ischemic compound KC 12291 prevents diastolic contracture in isolated atria by blockade of voltage-gated sodium channels.

Several lines of evidence support a fundamental role for voltage-gated sodium channels in mediating ischemic Na rise. We examined the effect of the novel anti-ischemic compound KC 12291 on veratridine-stimulated and lysophosphatidylcholine (LPC)-induced sustained sodium current (I(NAL)) mediated by sodium channels in isolated myocytes obtained from guinea-pig atria, by using the whole-cell patch-clamp technique. We also analyzed the effect of KC 12291 on veratridine- and LPC-induced contractures in isolated guinea-pig atria.

Changes in intracellular sodium and pH during ischaemia-reperfusion are attenuated by trimetazidine. Comparison between low- and zero-flow ischaemia.

Objective: The aim of this study was to investigate whether trimetazidine (TMZ; 10(-6)M), which has been shown to inhibit fatty acid oxidation, reduces the ionic imbalance induced by ischaemia and reperfusion, especially through an attenuation in intracellular changes in H(+) and Na(+).

Methods: Isovolumic rat hearts receiving 5.5 mM glucose and 1.

Slowly inactivating component of sodium current in ventricular myocytes is decreased by diabetes and partially inhibited by known Na(+)-H(+)Exchange blockers.

Recent evidence has suggested a major role for a slowly inactivating component of Na(+)current (I(NaL)) as a contributor to ischemic Na(+)loading. The purposes of this study were to investigate veratrine and lysophosphatidylcholine (LPC)-induced I(NaL)in single ventricular myocytes of normal and diabetic rats and to analyse the effects on this current of three pharmacological agents, known as Na(+)/H(+)exchange inhibitors, whose selectivity has been questioned in several studies. A decrease in Na(+)/H(+)exchange activity has been previously shown to be associated with diabetes, and this has been found to confer some protection to the diabetic heart after an episode of ischemia/reperfusion.

Decrease in sodium-calcium exchange and calcium currents in diabetic rat ventricular myocytes.

This study was designed in order to gain insight into possible changes in the inward sodium-calcium exchange current (INa-Ca) and the L-type calcium current (ICa), in ventricular myocytes isolated from streptozotocin-induced diabetic rats. Recordings were made using the nystatin-perforated patch technique which minimizes interference with the normal intracellular Ca2+ buffering mechanisms. The averaged INa-Ca current density elicited by Ca2+ current was smaller in diabetic than in normal myocytes at all potentials tested.

Ionic and metabolic imbalance as potential factors of ischemia reperfusion injury.

This study examined the influence of metabolic substrates on the effects of trimetazidine on functional and metabolic aspects of the ischemic reperfused heart. Isovolumic rat hearts were submitted to a 30-minute period of global mild ischemia (coronary flow decreased by an average of 70%) and then reperfused at constant preischemic coronary flow rate. Either glucose (11 mM) or glucose and palmitic acid (0.

HCO3(-)-dependent alkalinizing transporter in adult rat ventricular myocytes: characterization and modulation.

The present work was designed to identify the HCO3(-)-dependent alkalinizing carrier in ventricular myocytes of normal and diabetic adult rats and to determine to what extent this system contributes to acid-equivalent extrusion after an intracellular acidification. We also examined the possible influence of intracellular Ca2+ (Cai2-) and glycolytic inhibition on the carrier activation. Intracellular pH (pHi) was recorded using seminaphthorhodafluor-1.

Controversies on the sensitivity of the diabetic heart to ischemic injury: the sensitivity of the diabetic heart to ischemic injury is decreased.

Controversy exists as to whether the diabetic heart is more or less sensitive to ischemic injury. Although a considerable number of experimental studies have directly determined the effects of ischemia on the diabetic heart, there is still no general agreement as to whether metabolic changes within the myocardium contribute to the severity of ischemic injury. This paper reviews the evidence suggesting that the diabetic heart can actually be less sensitive to an episode of severe ischemia.

Modulation by pH0 and intracellular Ca2+ of Na(+)-H+ exchange in diabetic rat isolated ventricular myocytes.

We have previously shown that diabetes is associated with a decrease in Na(+)-H+ exchange activity in rat cardiac papillary muscle. The present work has been carried out in order to elucidate the factors responsible for such an alteration. Thus, we have studied the effects of pH0 and intracellular Ca2+ on Na(+)-H+ exchange in ventricular myocytes isolated from streptozotocin-induced diabetic rat hearts.

Effects of S20787 on pHi-regulating mechanisms in isolated rat ventricular myocytes.

Intracellular pH (pHi) regulation in the heart relies on the activity of three membrane mechanisms: the Na+/H+ exchange and an Na+, HCO3(-)-dependent transport, both activated after an acid load, and the Cl-/HCO(3-) exchange, activated by an intracellular alkalinization. Whereas several specific inhibitors of Na+/H+ exchange exist, distinguishing between the two HCO3(-)-dependent mechanisms remains difficult, especially near the steady state, because of the lack of specific inhibitors. To detect one such inhibitor, we tested the effects of S20787 on pHi regulation in the rat isolated ventricular myocytes.

Intracellular pH control mechanisms in the diabetic myocardium.

Intracellular pH (pHi) regulation and the consequences of this regulation may play a crucial role during ischaemia and especially on reperfusion after an ischaemic episode. A significant decrease in Na+/H+ exchange activity was first demonstrated in papillary muscles isolated from hearts of diabetic rats, and recently confirmed in diabetic rat isolated ventricular myocytes. This depressed activity of one of the major pHi regulatory mechanisms may afford some protection against ischaemia/reperfusion injury.

Altered Ca2+ handling in ventricular myocytes isolated from diabetic rats.

It has been suggested that alterations in intracellular Ca2+ homeostasis may be responsible for the development of diabetic cardiomyopathy. We have studied the effects of streptozotocin-induced diabetes on intracellular Ca2+ concentration ([Ca2+]i) in enzymically isolated rat ventricular myocytes. [Ca2+]i was measured using indo 1 or fluo 3.