Reactive Oxygen Species Mediate the Suppression of Arterial Smooth Muscle T-type Ca 2+ Channels by Angiotensin II.

Vascular T-type Ca2+ channels (CaV 3.1 and CaV 3.2) play a key role in arterial tone development. This study investigated whether this conductance is a regulatory target of angiotensin II (Ang II), a vasoactive peptide that circulates and which is locally produced within the arterial wall. Patch clamp electrophysiology performed on rat cerebral arterial smooth muscle cells reveals that Ang II (100 nM) inhibited T-type currents through AT1 receptor activation. Blocking protein kinase C failed to eliminate channel suppression, a finding consistent with unique signaling proteins enabling this response. In this regard, inhibiting NADPH oxidase (Nox) with apocynin or ML171 (Nox1 selective) abolished channel suppression highlighting a role for reactive oxygen species (ROS). In the presence of Ni2+ (50 µM), Ang II failed to modulate the residual T-type current, an observation consistent with this peptide targeting CaV 3.2. Selective channel suppression by Ang II impaired the ability of CaV 3.2 to alter spontaneous transient outward currents or vessel diameter. Proximity ligation assay confirmed Nox1 colocalization with CaV 3.2. In closing, Ang II targets CaV 3.2 channels via a signaling pathway involving Nox1 and the generation of ROS. This unique regulatory mechanism alters BKCa mediated feedback giving rise to a "constrictive" phenotype often observed with cerebrovascular disease.