RAT RENAL ARCADE SEGMENT EXPRESSES VASOPRESSIN-REGULATED WATER CHANNEL AND VASOPRESSIN V-2 RECEPTOR

The arcades are long, branched renal tubules which connect deep and mi d-cortical nephrons to cortical collecting ducts in the renal cortex, Because they are inaccessible by standard physiological techniques, th eir functions are poorly understood, In this paper, we demonstrate tha t the arcades are a site of expression of two proteins, aquaporin-2 (t he vasopressin-regulated water channel) and the V-2 vasopressin recept or, that are important to regulated water transport in the kidney, Usi ng a peptide-derived polyclonal antibody to aquaporin-2, quantitative ELISA in microdissected segments showed that aquaporin-2 is highly exp ressed in arcades and that the expression is increased in response to restriction of fluid intake, Immunocytochemistry revealed abundant aqu aporin-2 labeling of structures in the cortical labyrinth in a pattern similar to that of the Na+-Ca2+ exchanger and kallikrein, marker prot eins expressed in arcades but not in cortical collecting ducts. RT-PCR experiments demonstrated substantial aquaporin-2 and V-2 receptor mRN A in microdissected arcades. In situ hybridization, using S-35-labeled antisense cRNA probes for the V-2 receptor demonstrated strong labeli ng of both arcades and cortical collecting ducts, Thus, these results indicate that the arcades contain the specific proteins associated wit h vasopressin-regulated water transport, and may be a heretofore unrec ognized site of free water absorption.