Vasopressin receptor-mediated endocytosis in cells transfected with V₁-type vasopressin receptors

We examined the process of receptor-mediated endocytosis in A-9 lung fibroblast and chinese hamster ovary (CHO) cells transfected with the recently cloned vasopressin V_1a receptor (51). We used a fluorescent labeled vasopressin analog (rhodamine-mercaptopropionic acid lysine vasopressin) and radiolabeled vasopressin to examine this process in the two transfected cell lines. Both A-9 and CHO cells internalize vasopressin in a manner consistent with receptor-mediated endocytosis. A-9 cells internalize vasopressin more rapidly than CHO cells. The process is inhibited by vasopressin and by specific vasopressin V₁ receptor antagonists but not by specific V₂ receptor antagonists. Hypertonic sucrose inhibits endocytosis in both cell types suggesting a role of clathrin coated pits in the endocytosis of receptor in these cells. These cells are excellent models in which to examine the effect of receptor mutations on vasopressin receptor-mediated endocytosis.