Reduced Expression and Activation of Voltage-Gated Sodium Channels Contributes to Blunted Baroreflex Sensitivity in Heart Failure Rats

Voltage-gated sodium (Na-v) channels are responsible for initiation and propagation of action potential in the neurons. To explore the mechanisms of chronic heart failure (CHF)-induced baroreflex dysfunction, we measured the expression and current density of Na-v channel subunits (Na(v)1.7, Na(v)1.8, and Na(v)1.9) in the aortic baroreceptor neurons and investigated the role of Nay channels in aortic baroreceptor neuron excitability and baroreflex sensitivity in sham and CHF rats. CHF was induced by left coronary artery ligation. The development of CHF (6-8 weeks after the coronary ligation) was confirmed by hemodynamic and morphological characteristics. Immunofluorescent data indicated that Na(v)1.7 was expressed in A-type (myelinated) and C-type (unmyelinated) nodose neurons, but Na(v)1.8 and Na(v)1.9 were expressed only in C-type nodose neurons. Real-time RT-PCR and Western blot data showed that CHF reduced mRNA and protein expression levels of Nay channels in nodose neurons. In addition, using the whole-cell patch-clamp technique, we found that Nay current density and cell excitability of the aortic baroreceptor neurons were lower in CHF rats than that in sham rats. Aortic baroreflex sensitivity was blunted in anesthetized CHF rats, compared with that in sham rats. Furthermore, Nay channel activator (rATX II, 100 nM) significantly enhanced Na-v current density and cell excitability of aortic baroreceptor neurons and improved aortic baroreflex sensitivity in CHF rats. These results suggest that reduced expression and activation of the Nay channels are involved in the attenuation of baroreceptor neuron excitability, which subsequently contributes to the impairment of baroreflex in CHF state. (C) 2010 Wiley-Liss, Inc.