Angiotensin II enhances hyperpolarization-activated currents in rat aortic baroreceptor neurons: involvement of superoxide
As an endogenous physiologically active peptide, angiotensin (ANG) II plays an important role in the maintenance of blood pressure. In the arterial baroreceptor reflex (a pivotal regulator of blood pressure), aortic baroreceptor (AB) neurons located in the nodose ganglia (NG) are a primary afferent limb of the baroreflex. Hyperpolarization-activated currents (Ih) in the AB neurons contribute to the excitability of the AB neurons. Therefore, the present study was to measure the modulating effect of ANG II on the Ih in the primary AB neurons isolated from
rats. Data from immunofluorescent and Western blot analyses showed that protein of AT1 and AT2 receptors was expressed in the nodose neurons. In the whole cell patch-clamp recording, ANG II concentration dependently enhanced the Ih density in the AB neurons. ANG II also decreased membrane excitability in the AB neurons. AT1 receptor antagonist (losartan) but not AT2
receptor antagonist (PD-123,319) totally abolished the effect of ANG II on the Ih and neuronal excitability. In addition, NADPH oxidase inhibitor (apocynin) and superoxide scavenger (tempol) also significantly blunted the ANG II-induced increase of the Ih and decrease of the membrane excitability in the AB neurons. Furthermore, losartan, apocynin, or tempol significantly attenuated the
superoxide overproduction in the NG tissues induced by ANG II. These results suggest that ANG II-NADPH oxidase-superoxide signaling can activate the Ih and subsequently decrease the membrane excitability of rat AB neurons.