Abstract —Caveolae are membrane domains that have been implicated in signal transduction, and caveolins are major structural components of these domains. We found that all reported caveolin isoforms (caveolin-1, -2, and -3) were expressed in vascular smooth muscle cells (VSMCs); however, only caveolin-1 mRNA was regulated by angiotensin II (Ang II). Ang II (100 nmol/L) increased caveolin-1 mRNA, with a peak at 2 hours (193±6% of control, P <0.01, n=4). In contrast, Ang II significantly decreased caveolin-1 protein, with a nadir at 4 hours (64±5% of control, P <0.01, n=6). [ ³⁵ S]Methionine labeling showed that Ang II increased caveolin biosynthesis (226±33% of control labeling at 4 hours), suggesting that the transient decrease in caveolin protein levels is due to increased degradation. When cells were fractionated with sucrose, on agonist stimulation, AT ₁ receptors appeared in fraction 5 where caveolin was fractionated. This migration was blocked by low temperature and treatment with phenylarsine oxide, interventions that interfere with agonist-induced Ang II type 1 (AT ₁ ) receptor sequestration and tonic phase signaling. In addition, caveolin-1 coimmunoprecipitates with AT ₁ receptor only on agonist stimulation. These data support the concept that the caveola is a specialized signaling domain in VSMCs that can be dynamically accessed by the AT ₁ receptor. Because of the signaling and coupling proteins that are localized in caveolae and because of evidence that these proteins may interact directly with caveolin, caveola–AT ₁ receptor interaction likely represents an important focus for dynamic control of receptor signaling in VSMCs.