New insights in the contribution of voltage-gated Na(v) 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.


RESULTS
Na(v) channels were detected in the aortic media by Western blot analysis and double immunofluorescence labeling for Na(v) channels and smooth muscle alpha-actin using specific antibodies. In parallel, using real time RT-PCR, we identified three Na(v) transcripts: Na(v)1.2, Na(v)1.3, and Na(v)1.5. Only the Na(v)1.2 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 microM) and blocked by TTX (1 microM). KB-R7943, an inhibitor of the reverse mode of the Na(+)/Ca(2+) exchanger, mimicked the effect of TTX and had no additive effect in presence of TTX.


CONCLUSIONS
These results define a new role for Na(v) channels in arterial physiology, and suggest that the TTX-sensitive Na(v)1.2 isoform, together with the Na(+)/Ca(2+) exchanger, contributes to the contractile response of aortic myocytes at physiological range of membrane depolarization.
Fort
Aurélie
A
INSERM U637, Université Montpellier 1 & 2, Montpellier, France.
Cordaillat
Magali
M
Thollon
Catherine
C
Salazar
Guillermo
G
Mechaly
Ilana
I
Villeneuve
Nicole
N
Vilaine
Jean-Paul
JP
Richard
Sylvain
S
Virsolvy
Anne
A
D000818:Animals; D001011:Aorta / Q000378:metabolism*; D004594:Electrophysiology / Q000379:methods; D008297:Male; D008564:Membrane Potentials; D032342:Muscle Cells / Q000473:pathology; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D009711:Nucleotides / Q000737:chemistry; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000737:chemistry* / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000737:chemistry; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D009711:Nucleotides; D020033:Protein Isoforms; C568253:Scn2A protein, rat; D015222:Sodium Channels; D019831:Sodium-Calcium Exchanger; D013890:Thiourea