Angiotensin II Disrupts Neurovascular Coupling by Potentiating Calcium Increases in Astrocytic Endfeet

BACKGROUND: Angiotensin II (Ang II), a critical mediator of hypertension, impairs neurovascular coupling. Since astrocytes are key regulators of neurovascular coupling, we sought to investigate whether Ang II impairs neurovascular coupling through modulation of astrocytic Ca(2+) signaling. METHODS AND RESULTS: Using laser Doppler flowmetry, we found that Ang II attenuates cerebral blood flow elevations induced by whisker stimulation or the metabotropic glutamate receptors agonist, 1S, 3R‐1‐aminocyclopentane‐trans‐1,3‐dicarboxylic acid (P<0.01). In acute brain slices, Ang II shifted the vascular response induced by 1S, 3R‐1‐aminocyclopentane‐trans‐1,3‐dicarboxylic acid towards vasoconstriction (P<0.05). The resting and 1S, 3R‐1‐aminocyclopentane‐trans‐1,3‐dicarboxylic acid–induced Ca(2+) levels in the astrocytic endfeet were more elevated in the presence of Ang II (P<0.01). Both effects were reversed by the AT1 receptor antagonist, candesartan (P<0.01 for diameter and P<0.05 for calcium levels). Using photolysis of caged Ca(2+) in astrocytic endfeet or pre‐incubation of 1,2‐Bis(2‐aminophenoxy)ethane‐N,N,N',N'‐tetra‐acetic acid tetrakis (acetoxymethyl ester), we demonstrated the link between potentiated Ca(2+) elevation and impaired vascular response in the presence of Ang II (P<0.001 and P<0.05, respectively). Both intracellular Ca(2+) mobilization and Ca(2+) influx through transient receptor potential vanilloid 4 mediated Ang II‐induced astrocytic Ca(2+) elevation, since blockade of these pathways significantly prevented the intracellular Ca(2+) in response to 1S, 3R‐1‐aminocyclopentane‐trans‐1,3‐dicarboxylic acid (P<0.05). CONCLUSIONS: These results suggest that Ang II through its AT1 receptor potentiates the astrocytic Ca(2+) responses to a level that promotes vasoconstriction over vasodilation, thus altering cerebral blood flow increases in response to neuronal activity.