Gene expression in the thin limbs of Henle of the waterrestricted rat

Abstract

Sodium and water homeostasis and the formation of concentrated urine depend upon the generation of a steep osmotic gradient within the renal medulla. Although the mechanism of this process remains controversial, the descending thin limbs (DTLs) and ascending thin limbs (ATLs) of the loops of Henle play important roles. Our goal was to identify genes that may be involved in the urine concentrating mechanism and to quantify their transcript levels in the DTLs and ATLs. Using real‐time PCR, we analyzed transcripts in isolated DTLs and ATLs of water‐restricted rats. Claudin 4 (CLDN4), sodium‐dependent glucose transporter 1 (NaGLT1), sodium glucose cotransporter 1 (SGLT1), and sodium myo‐inositol cotransporter 1 (SMIT1) were present in both types of tubules and their levels increased in the ATLs after 72h of water restriction. Chloride channel (Clcnka) mRNA in the ATLs and urea transporter mRNA (UT‐A2) in the DTLs increased. We also identified a novel variant of SGLT1 and four variants of the arginine vasopressin receptor 2 (AVPR2). Our results indicate that in addition to the previously characterized aquaporins and urea transporters, several other genes and their products may be involved in the movement of ions and solutes in the thin limbs of Henle. Further studies will determine how these genes contribute to urine concentration. NIDDK DK083338