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Background: Despite increasing evidence for the presence of voltage-gated Na+ channels (Nav) isoforms and measurements of Nav channel currents with the patch-clamp technique in arterial myocytes, no information is available to date as to whether or not Nav channels play a functional role in arteries. The aim of the present work was to look for a physiological role of Nav channels in the control of rat aortic contraction. Methodology/Principal Findings: Nav channels were detected in the aortic media by Western blot analysis and double immunofluorescence labeling for Nav channels and smooth muscle α-actin using specific antibodies. In parallel, using real time RT-PCR, we identified three Nav transcripts: Nav1.2, Nav1.3, and Nav1.5. Only the Nav1.2 isoform was found in the intact media and in freshly isolated myocytes excluding contamination by other cell types. Using the specific Nav channel agonist veratridine and antagonist tetrodotoxin (TTX), we unmasked a contribution of these channels in the response to the depolarizing agent KCl on rat aortic isometric tension recorded from endothelium-denuded aortic rings. Experimental conditions excluded a contribution of Nav channels from the perivascular sympathetic nerve terminals. Addition of low concentrations of KCl (2-10 mM), which induced moderate membrane depolarization (e.g., from -55.9±1.4 mV to -45.9±1.2 mV at 10 mmol/L as measured with microelectrodes), triggered a contraction potentiated by veratridine (100 μM) and blocked by TTX (1 μM). KB-R7943, an inhibitor of the reverse mode of the Na+/Ca2+ exchanger, mimicked the effect of TTX and had no additive effect in presence of TTX. Conclusions/Significance: These results define a new role for Nav channels in arterial physiology, and suggest that the TTXsensitive Nav1.2 isoform, together with the Na+/Ca2+ exchanger, contributes to the contractile response of aortic myocytes at physiological range of membrane depolarization. [ABSTRACT FROM AUTHOR]

Objective: As a result of oxidative stress to membrane lipid matrix, the peroxidation of polyunsaturated fatty acids induced the transient formation of lipid hydroperoxides (ROOM). The aim of this study was to evaluate the damaging effects of ROOH on the cardiac cell and the link between the alterations observed and intracellular calcium overload. Methods: Necrosis of cultured rat cardiac cells was determined by measuring the release of lactate dehydrogenase (LDH). In guinea-pig papillary muscles, action potential (AP) and isometric tension were recorded with standard microelectrodes and a transducer, respectively. The reactive oxygen species (ROS) scavenging properties of tested compounds were determined using a cell-free model of lipid photoperoxidation. Results: 15(S)-HpETE (15(S)-hydroperoxyeicosatetraenoic acid), an arachidonic acid hydroperoxide, induced a concentration-dependent loss of cardiomyocytes membrane integrity. The release of LDH induced by 15(S)-HpETE (30 μM) was prevented by a ROS scavenger, BW755C (10 μM), but not by a sarcolemmal calcium channel blocker, Amlodipine (10 μM), or a calcium overload protective agent, R56865 (10 μM). Cardiomyocytes necrosis induced by calcium paradox was prevented by Amlodipine (10 μM) and R56865 (10 μM), but not by BW755C (10 μM). Superfusion of papillary muscles with 15(S)-HpETE (20 μM) induced a membrane depolarization and a marked reduction in the AP amplitude and duration. Concomitantly, a transient positive inotropic effect and a progressive rise in diastolic tension were observed. These alterations were maximal after 15 min and associated with delayed after-depolarizations (DADs) and after-contractions. Every alteration was inhibited by BW755C (10 μM) and R56865 (30 μM), but not by Amlodipine (1 μM). Ryanodine (1 μM), a blocker of sarcoplasmic reticulum calcium channel, only prevented the appearance of DADs and after-contractions. Only BW755C exibited ROS scavenging properties. Conclusions: ROOH induced enzyme leakage and electromechanical alterations in cardiac cells. These effects of ROOH implicated oxidative mechanisms and resulted in an intracellular calcium overload. [ABSTRACT FROM PUBLISHER]