ARGININE-VASOPRESSIN RECEPTOR INTERNALIZATION AND RECYCLING IN RAT RENAL COLLECTING TUBULES

Arginine vasopressin (AVP) binds to two distinct receptors to initiate vasopressor (V1 receptor) and hydroosmotic actions (V2 receptor). Int ernalization and recycling of the V1 receptor in cultured vascular smo oth muscle cells and hepatocytes have recently been demonstrated. Howe ver, the receptor cycle of the AVP V2 receptor in the renal collecting tubules has not yet been well defined. Therefore, the present study w as undertaken to investigate the AVP V2 receptor cycle, including AVP binding to the surface receptor, internalization and potential recycli ng in isolated outer medullary collecting tubules. The maximal AVP sur face binding was reached in 10 min, and 25 mu g/ml trypsin completely inhibited the surface binding. A Scatchard plot of I-125-AVP surface b inding indicated a single population of V2 receptors with a Kd of 1.92 x10(-9) M and a Bmax of 1.77x10(-11) M or 590 fmoles/mg protein. 81.7% (72-85%) of specific bound receptor was internalized (specific surfac e binding: 742.8+/-111.1 vs internalized binding: 607.3+/-27.8 fmoles bound/mg protein). More than 90% of surface bound receptor was recycle d to the cell surface after internalization (control surface binding: 584.0+/-64.0 vs recycled surface binding: 546.6+/-32.0 fmoles bound/mg protein). Cycloheximide (40 mu g/ml) did not inhibit the receptor rec ycling (control recycled surface binding: 546.6+/-32.0 vs cycloheximid e recycled surface binding: 505.0+/-54.8 fmoles bound/mg protein), thu s suggesting that the receptors were not resynthesized after dissociat ion from the receptor-ligand complex. These studies therefore demonstr ate that the AVP V2 receptor is internalized and recycled in the rat r enal collecting tubule.