Superoxide Mediates Angiotensin II–Induced Influx of Extracellular Calcium in Neural Cells

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Abstract
We recently demonstrated that superoxide (O2•−) is a key signaling intermediate in central angiotensin II (Ang II)-elicited blood pressure and drinking responses, and that hypertension caused by systemic Ang II infusion involves oxidative stress in cardiovascular nuclei of the brain. Intracellular Ca2+ is known to play an important role in Ang II signaling in neurons, and it is also linked to reactive oxygen species mechanisms in neurons and other cell types. However, the potential cross-talk between Ang II, O2•−, and Ca2+ in neural cells remains unknown. Using mouse neuroblastoma Neuro-2A cells, we tested the hypothesis that O2•− radicals are involved in the Ang II–induced increase in intracellular Ca2+ concentration ([Ca2+]i) in neurons. Ang II caused a rapid time-dependent increase in [Ca2+]i that was abolished in cells bathed in Ca2+-free medium or by pretreatment with the nonspecific voltage-gated Ca2+ channel blocker CdCl2, suggesting that voltage-sensitive Ca2+ channels are the primary source of Ang II–induced increases in [Ca2+]i in this cell type. Overexpression of cytoplasm-targeted O2•− dismutase via an adenoviral vector (AdCuZnSOD) efficiently scavenged Ang II–induced increases in intracellular O2•− and markedly attenuated the increase in [Ca2+]i caused by this peptide. Furthermore, adenoviral-mediated expression of a dominant-negative isoform of Rac1 (AdN17Rac1), a critical component for NADPH oxidase activation and O2•− production, significantly inhibited the increase in [Ca2+]i after Ang II stimulation. These data provide the first evidence that O2•− is involved in the Ang II–stimulated influx of extracellular Ca2+ in neural cells and suggest a potential intracellular signaling mechanism involved in Ang II–mediated oxidant regulation of central neural control of blood pressure.