Mechanisms of Na+-Ca2+ Exchange Inhibition by Amphiphiles in CardiacMyocytes: Importance of Transbilayer Movement

The membrane lipid environment and lipid signaling pathways are potentially involved in the modulation of the activity of the cardiac Na+-Ca2+ exchanger (NCX). In the present study biophysical mechanisms of interactions of amphiphiles with the NCX and the functional consequences were examined. For this purpose, intracellular Ca2+ concentration jumps were generated by laser-flash photolysis of caged Ca2+ in guinea-pig ventricular myocytes and Na+-Ca2+ exchange currents (INa/Ca) were recorded in the whole-cell configuration of the patch-clamp technique. The inhibitory effect of amphiphiles increased with the length of the aliphatic chain between C7 and C10 and was more potent with cationic or anionic head groups than with uncharged head groups. Long-chain cationic amines (C12) exhibited a cut-off in their efficacy in INa/Ca inhibition. Analysis of the time-course, comparison with the Ni2+-induced INa/Ca block and confocal laser scanning microscopy experiments with fluorescent lipid analogs (C6- and C12-NBD-labeled analogs) suggested that amphiphiles need to be incorporated into the membrane. Furthermore, NCX block appears to require transbilayer movement of the amphiphile to the inner leaflet ("flip”). We conclude that both, hydrophobic and electrostatic interactions between the lipids and the NCX may be important factors for the modulation by lipids and could be relevant in cardiac diseases where the lipid metabolism is altere

Potential Relevance of α1-Adrenergic Receptor Autoantibodies in Refractory Hypertension

-AAB might have a mechanistic role and could represent a therapeutic target. in cardiomyocytes and induce mesentery artery segment contraction.-AAB in hypertensive patients, and the notion of immunity as a possible cause of hypertension

Les paradoxes du financement de la croissance

National audienceL'entreprise agroalimentaire moyenne du Languedoc-Roussillon en 1997 emploie 15 salariés pour un chiffre d'affaires moyen de 35 millions de francs en croissance de 7% sur 1996. Elle produit 12 millions de francs de valeur ajoutée et obtient un résultat annuel net de 600 000 F. 41% des entreprises exportent. En matière d'investissements, plus d'un tiers des entreprises agroalimentaires du Languedoc-Roussillon font preuve d'un grand dynamisme en investissant très largement dans leur outil de production, mais aussi dans la structuration ou l'amélioration de leurs moyens commerciaux. Les comportements financiers semblent plus liés à des critères de structure de propriété, et donc de gouvernance, qu'à une logique de filière ou de taille d'entreprise

Mechanisms of Na +-Ca 2+ Exchange Inhibition by Amphiphiles in Cardiac Myocytes: Importance of Transbilayer Movement

Abstract. The membrane lipid environment and lipid signaling pathways are potentially involved in the modulation of the activity of the cardiac Na +-Ca 2+ exchanger (NCX). In the present study biophysical mechanisms of interactions of amphiphiles with the NCX and the functional consequences were examined. For this purpose, intracellular Ca 2+ concentration jumps were generated by laser-flash photolysis of caged Ca 2+ in guinea-pig ventricular myocytes and Na +-Ca 2+ exchange currents (INa/Ca) were recorded in the whole-cell configuration of the patchclamp technique. The inhibitory effect of amphiphiles increased with the length of the aliphatic chain between C7 and C10 and was more potent with cationic or anionic head groups than with uncharged head groups. Long-chain cationic amines (C 12) exhibited a cut-off in their efficacy in I Na/Ca inhibition. Analysis of the time-course, comparison with the Ni 2+-induced INa/Ca block and confocal laser scanning microscopy experiments with fluorescent lipid analogs (C6- and C12-NBD-labeled analogs) suggested that amphiphiles need to be incorporated into the membrane. Furthermore, NCX block appears to require transbilayer movement of the amphiphile to the inner leaflet (‘‘flip’’). We conclude that both, hydrophobic and electrostatic interactions between the lipids and the NCX may be important factors for the modulation by lipids and could be relevant in cardiac diseases where the lipid metabolism is altered. Key words: Sodium-calcium exchange — Cardiac myocyte — Caged calcium — Excitation-contractio

Selective inhibition of persistent sodium current by F 15845 prevents ischaemia-induced arrhythmias

BACKGROUND AND PURPOSE: Myocardial ischaemia is associated with perturbations of electrophysiological profile of cardiac myocytes. The persistent sodium current (I(Nap)) is one of the major contributors to ischaemic arrhythmias and appears as an attractive therapeutic target. We investigated the effects of F 15845, a new anti-anginal drug on I(Nap) and in integrative models of I(Nap)-induced arrhythmias. EXPERIMENTAL APPROACH: Sodium current was investigated using patch clamp technique on wild-type and ΔKPQ-mutated hNav1.5 channels transfected in HEK293 cells. Effects of F 15845 on action potentials (APs) were studied by the glass microelectrode technique and its anti-arrhythmic activities were investigated in ischaemia- and aconitine-induced arrhythmias in the rat. KEY RESULTS: We demonstrated that F 15845 is a potent blocker of I(Nap) acting from the extracellular side of the channel. Blockade of I(Nap) was voltage dependent and characterized by an almost pure tonic block. F 15845 shortened AP from rabbit Purkinje fibres, confirming its lack of pro-arrhythmic activity, and prevented AP lengthening induced by the I(Nap) activator veratridine. F 15845 did not affect APs from rabbit atria and guinea pig papillary muscle where I(Nap) is not functional, confirming its inability to affect other cardiac ionic currents. F 15845 was effective at preventing fatal ventricular fibrillation and ventricular tachycardia during coronary ligation without modifying heart rate and blood pressure, and dose dependently increased the dose threshold of aconitine required to induce ventricular arrhythmias. CONCLUSIONS AND IMPLICATIONS: F 15845, a novel anti-anginal drug targeting I(Nap), demonstrates new anti-arrhythmic properties which may be of therapeutic benefit against ischaemia-induced arrhythmia

Agonist specific L-type Ca 2+-current stimulation in ventricular myocytes by a novel steroid-like compound

In cardiac muscle the amplitude of Ca 2+ transients can be increased by enhancing Ca 2+ influx. Among the processes leading to increased Ca 2+ influx, agonists of the L-type Ca 2+-channel can play an important role. Known pharmacological Ca 2+-channel agonists act on different binding sites on the channel protein, which may lead not only to enhanced peak currents, but also to distinct changes in other biophysical characteristics of the current. In this study, membrane currents were recorded with the patch–clamp technique in the whole-cell configuration in guinea pig isolated ventricular myocytes in combination with confocal fluorescence Ca 2+ imaging techniques and a variety of pharmacological tools. Testing a new positive inotropic steroid-like compound, we found that it increased the L-type Ca 2+-current by 2.5-fold by shifting the voltagedependence of activation by 20.2 mV towards negative potentials. The dose–response relationship revealed two vastly different affinities (EC50(high-affinity) = 4.5 ± 1.7 nM, EC50(low-affinity) = 8.0 ± 1.1 �M) exhibiting differential pharmacological interactions with three classes of Ca 2+-current antagonists, suggesting more than one binding site on the channel protein. Therefore, we identified and characterized a novel positive inotropic compound (F90927) as a member of a new class of Ca 2+-channel agonists exhibiting unique features, which set it apart from other presently known L-type Ca 2+-channel agonists

A direct relationship between plasma aldosterone and cardiac L-type Ca(2+) current in mice

Aldosterone is involved in a variety of pathophysiological processes that ultimately cause cardiovascular diseases. Despite this, the physiological role of aldosterone in heart function remains elusive. We took advantage of transgenic mouse models characterized by a renal salt-losing (SL) or salt-retaining (SR) phenotype, thus exhibiting chronically high or low plasma aldosterone levels, respectively, to investigate the chronic effects of aldosterone in cardiomyocytes devoid of pathology. On a diet containing normal levels of salt, these animals do not develop any evidence of cardiovascular disease. Using the whole cell patch-clamp technique on freshly isolated adult ventricular cardiomyocytes, we observed that the amplitude of L-type Ca(2+) currents (I(Ca)) correlates with plasma aldosterone levels. Larger values of I(Ca) are associated with high aldosterone concentrations in SL models, whereas smaller values of I(Ca) were observed in the SR model. Neither the time- nor the voltage-dependent properties of I(Ca) varied measurably. In parallel, we determined whether modulation of I(Ca) by blood concentration of aldosterone has a major physiological impact on the excitation–contraction coupling of the cardiomyocytes. Action potential duration, [Ca(2+)](i) transient amplitude and contraction are increased in the SL model and decreased in the SR model. In conclusion, we demonstrate that the blood concentration of aldosterone exerts chronic regulation of I(Ca) in mouse cardiomyocytes. This regulation has important consequences for excitation–contraction coupling and, potentially, for other Ca(2+)-regulated functions in cardiomyocytes