Angiotensin II type 2 receptor-coupled nitric oxide production modulates free radical availability and voltage-gated Ca currents in NTS neurons

Wang G, Coleman CG, Glass MJ, Zhou P, Yu Q, Park L, Anrather J, Pickel VM, Iadecola C. Angiotensin II type 2 receptorcoupled nitric oxide production modulates free radical availability and voltage-gated Ca currents in NTS neurons. Am J Physiol Regul Integr Comp Physiol 302: R1076–R1083, 2012. First published February 29, 2012; doi:10.1152/ajpregu.00571.2011.—The medial region of the nucleus tractus solitarius (mNTS) is a key brain stem site controlling cardiovascular function, wherein ANG II modulates neuronal L-type Ca currents via activation of ANG II type 1 receptors (AT1R) and production of reactive oxygen species (ROS). ANG II type 2 receptors (AT2R) induce production of nitric oxide (NO), which may interact with ROS and modulate AT1R signaling. We sought to determine whether AT2R-mediated NO production occurs in mNTS neurons and, if so, to elucidate the NO source and the functional interaction with AT1R-induced ROS or Ca influx. Electron microscopic (EM) immunolabeling showed that AT2R and neuronal NO synthase (nNOS) are coexpressed in neuronal somata and dendrites receiving synapses in the mNTS. In the presence of the AT1R antagonist losartan, ANG II increased NO production in isolated mNTS neurons, an effect blocked by the AT2R antagonist PD123319, but not the angiotensin (1–7) antagonist D-Ala. Studies in mNTS neurons of nNOS-null or endothelial NOS (eNOS)-null mice established nNOS as the source of NO. ANG II-induced ROS production was enhanced by PD123319, the NOS inhibitor N-nitro-Larginine (LNNA), or in nNOS-null mice. Moreover, in the presence of losartan, ANG II reduced voltage-gated L-type Ca current, an effect blocked by PD123319 or LNNA. We conclude that AT2R are closely associated and functionally coupled with nNOS in mNTS neurons. The resulting NO production antagonizes AT1R-mediated ROS and dampens L-type Ca currents. The ensuing signaling changes in the NTS may counteract the deleterious effects of AT1R on cardiovascular function.