SEGMENTAL LOCALIZATION OF UREA TRANSPORTER MESSENGER-RNAS IN RAT-KIDNEY

Renal epithelia express at least two distinct urea transporter mRNAs, termed UT1 and UT2, that are derived from a single UT gene by alternat ive splicing. Previous immunolocalization studies using a polyclonal a ntibody that does not distinguish between the protein products of thes e two transcripts revealed that expression of urea transporter protein is restricted to inner medullary collecting ducts and descending thin limbs of Henle's loop. To identify which transcripts account for prot ein expression in these two structures, we carried out reverse transcr iption-polymerase chain reaction studies in microdissected structures using UT1- and UT2-specific primers. UT1 mRNA was detected only in the inner medullary collecting duct, consistent with its identification a s the vasopressin-regulated urea transporter. In contrast, UT2-mRNA wa s detected in the late part of descending thin limbs of short loops of Henle and in the inner medullary part of descending thin limbs of lon g loops of Henle. This localization is consistent with the predicted r ole of UT2 in medullary urea recycling. Thus, in conjunction with fore going physiological studies, our data indicate that these transporters play central roles in the urinary concentrating mechanism.