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

Abstract

Vascular T-type Ca ²⁺ channels (Ca _V3.1 and Ca _V3.2) 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 AT ₁ 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 Ni ²⁺ (50 µM), Ang II failed to modulate the residual T-type current, an observation consistent with this peptide targeting Ca _V3.2. Selective channel suppression by Ang II impaired the ability of Ca _V3.2 to alter spontaneous transient outward currents or vessel diameter. Proximity ligation assay confirmed Nox1 colocalization with Ca _V3.2. In closing, Ang II targets Ca _V3.2 channels via a signaling pathway involving Nox1 and the generation of ROS. This unique regulatory mechanism alters BK _Ca mediated feedback giving rise to a “constrictive” phenotype often observed with cerebrovascular disease.