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). Internalization and recycling of the V1 receptor in cultured vascular smooth muscle cells and hepatocytes have recently been demonstrated. However, the receptor cycle of the AVP V2 receptor in the renal collecting tubules has not yet been well defined. Therefore, the present study was undertaken to investigate the AVP V2 receptor cycle, including AVP binding to the surface receptor, internalization and potential recycling in isolated outer medullary collecting tubules. The maximal AVP surface 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 binding indicated a single population of V2 receptors with a Kd of 1.92x10(-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 surface binding: 742.8+/-111.1 vs internalized binding: 607.3+/-27.8 fmoles bound/mg protein). More than 90% of surface bound receptor was recycled 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 recycling (control recycled surface binding: 546.6+/-32.0 vs cycloheximide recycled surface binding: 505.0+/-54.8 fmoles bound/mg protein), thus suggesting that the receptors were not resynthesized after dissociation from the receptor-ligand complex. These studies therefore demonstrate that the AVP V2 receptor is internalized and recycled in the rat renal collecting tubule.