New Insights in the Contribution of Voltage-Gated Nav Channels to Rat Aorta Contraction.

Background: Despite increasing evidence for the presence of voltage-gated Na⁺ channels (Na_v) isoforms and measurements of Na_v channel currents with the patch-clamp technique in arterial myocytes, no information is available to date as to whether or not Na_v channels play a functional role in arteries. The aim of the present work was to look for a physiological role of Na_v channels in the control of rat aortic contraction. Methodology/Principal Findings: Na_v channels were detected in the aortic media by Western blot analysis and double immunofluorescence labeling for Na_v channels and smooth muscle α-actin using specific antibodies. In parallel, using real time RT-PCR, we identified three Na_v transcripts: Na_v1.2, Na_v1.3, and Na_v1.5. Only the Na_v1.2 isoform was found in the intact media and in freshly isolated myocytes excluding contamination by other cell types. Using the specific Na_v 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 Na_v 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 Na_v channels in arterial physiology, and suggest that the TTXsensitive Na_v1.2 isoform, together with the Na⁺/Ca²⁺ exchanger, contributes to the contractile response of aortic myocytes at physiological range of membrane depolarization. [ABSTRACT FROM AUTHOR]