T he renin-angiotensin system (RAS) is well known for its physiological and pathophysiological roles in the regulation of blood pressure (BP) and cardiovascular function. 1,2 A new component of the RAS, angiotensin-converting enzyme (ACE) type 2 has been identified, from human heart failure ventricle and lymphoma cDNA libraries (reviewed elsewhere 3,4 ). Although the angiotensin-converting enzyme type 2 (ACE2) transcript was first described in heart, kidney and testis, additional studies reported ACE2 mRNA in rat medulla oblongata 4 and ACE2 activity in mouse brain. 5 Recently, we showed the presence of both ACE2 protein and mRNA widespread throughout the murine brain, in regions involved in the central regulation of cardiovascular function as well as noncardiovascular regions. 6 ACE2 converts Ang II into the vasodilatory peptide Ang-(1-7) with an affinity 400-fold higher than for Ang I. 7 In the central nervous system (CNS), Ang-(1-7) has been shown to enhance sensitivity of the bradycardic component of the cardiac baroreceptor reflex 8 and to promote vasodilation in hypertensive animals. 9,10 As a key enzyme in generating Ang-(1-7), ACE2 is thought to be a pivotal player in central BP regulation. 3,5 Several evidences from various laboratories have shown the beneficial effects of peripheral ACE2 in the regulation of cardiovascular hypertrophy and BP control. 10 -12 In the CNS, using a lentivirus coding for ACE2, Yamazato et al previously showed that ACE2 overexpression in the rostral ventrolateral medulla, could reverse hypertension in spontaneously hypertensive rats (SHR). 13 More recently, we reported that brain-targeted ACE2 overexpression in the subfornical organ (SFO) prevents the acute Ang II-mediated pressor and Original

An exaggerated exercise pressor reflex (EPR) causes excessive sympatho-excitation and exercise intolerance during physical activity in the chronic heart failure (CHF) state. Muscle afferent sensitization contributes to the genesis of the exaggerated EPR in CHF. However, the cellular mechanisms underlying muscle afferent sensitization in CHF remain unclear. Considering that voltage-gated potassium (Kv) channels critically regulate afferent neuronal excitability, we examined the potential role of Kv channels in mediating the sensitized EPR in male CHF rats. Real time RT-PCR and western blotting experiments demonstrate that both mRNA and protein expressions of multiple Kv channel isoforms (Kv1.4, Kv3.4, Kv4.2 and Kv4.3) were downregulated in lumbar DRGs of CHF rats compared to sham rats. Immunofluorescence data demonstrates significant decreased Kv channel staining in both NF200-positive and IB4-positive lumbar DRG neurons in CHF rats compared to sham rats. Data from patch clamp experiments demonstrate that the total Kv current, especially IA, was dramatically decreased in medium-sized IB4-negative muscle afferent neurons (a subpopulation containing mostly Aδ neurons) from CHF rats compared to sham rats, indicating a potential functional loss of Kv channels in muscle afferent Aδ neurons. In in vivo experiments, adenoviral overexpression of Kv4.3 in lumbar DRGs for one week attenuated the exaggerated EPR induced by muscle static contraction and the mechanoreflex by passive stretch without affecting the blunted cardiovascular response to hindlimb arterial injection of capsaicin in CHF rats. These data suggest that Kv channel dysfunction in DRGs play a critical role in mediating the exaggerated EPR and muscle afferent sensitization in CHF.

Central ACE2 prevents the development of hypertension induced by chronic AngII infusion in transgenic mice (SA) overexpressing ACE2 in the brain. To elucidate the mechanisms involved, we investigated the expression of NOS isoforms (immunohistochemistry) and NO release (free radical measurement) in the brain of these mice. At baseline, ACE2 over‐expression was associated with increased (Relative Intensity, RI) nNOS (1.9 ±0.4), eNOS (1.5 ±0.1), phosphorylated‐eNOS‐Ser1177/Thr495 ratio (3.4 ±0.2), an index of phosphorylation vs. dephosphorylation and NO release (3.57 ±0.02 μM) vs. non‐transgenic (NT) littermates (1.0 ±0.1 RI and 2.95 ±0.11 μM, respectively, P<0.05). AngII infusion dramatically reduced nNOS (1.4 ±0.3) and eNOS (0.8 ±0.1) expression; (P<0.05) and NO release (2.68 ±0.19 μM) in SA but it remained significantly higher than in NT (nNOS: 0.4 ±0.03; eNOS: 0.4 ±0.1; NO: 1.82 ±0.22 μM, P<0.05) mice. Interestingly, Ang II+Mas blocker dramatically decreased the Phospho‐eNOS‐Ser1177/Thr495 ratio (0.7 ±0.02) compared to SA mice infused with AngII alone (3.6 ±0.5, P<0.05) and further reduced NO levels (1.75 ±0.08 μM). These data suggest that ACE2 exerts its modulatory effects partly through up‐regulation of NOS expression and phosphorylation, reinforcing Ang‐(1–7)‐mediated NO release in the brain, thus preventing the development of neurogenic hypertension. (AHA 0825459E, NIH RR018766 and HL093178)