Accessory proteins and alpha 1D‐AR function in ASMCs

α 1 adrenergic receptors (AR) play important roles in the regulation of vascular tone and blood pressure. The roles of α 1B and α 1A have been well characterized, but the α 1D receptor has been more difficult to study due to its inefficient trafficking in cell culture models. Recently, it has been shown that the α 1D can become properly trafficked if the N‐terminus is removed, and putative chaperone molecules have been identified for the full‐length receptor. We have found additional binding partners using a GST‐tagged C‐terminal portion of α 1D , and a tandem affinity purification method (TAP) for both the full length and C‐terminal portions of the α 1D receptor. We complemented this proteomics search for binding partners by looking specifically at one associated protein, R egulator of G ‐protein S ignaling 2 (RGS2), in primary cultures of aortic smooth muscle cells isolated from C57/B16 wild type and RGS2 −/− mice. α 1D is the only α 1 AR in abundance in the aorta, thereby allowing a detailed study of α 1D response in primary culture without pollution with α 1A or α 1B responses. It is believed that RGS2 plays a role in regulation of signaling by binding the C‐tail of α 1D , but the nature of this role remains unclear. We used the Ca 2+ indicator Fluo‐4 AM to compare the response of α 1D through Gq‐coupled mechanisms to α 1 AR agonists in wild type and RGS2 −/− mouse aortic smooth muscle cells. We found a significant difference in the magnitude and duration of the response in response to α 1D agonists.