Isolation of a cDNA for rat CHIP28 water channel: high mRNA expression in kidney cortex and inner medulla.

The cDNA coding for the rat CHIP28 water channel was isolated from a kidney library. At the amino acid level, rat CHIP28 is 93% identical to the recently published human protein (1). Expression of rat CHIP28 mRNA was highest in the renal inner medulla, unchanged during antidiuresis and twice the level expressed in outer cortex, with lower expression levels also apparent in parotid gland, urinary bladder and prostate. The evidence suggests that CHIP28 water channels in the ADH-sensitive collecting tubules are identical to those of the ADH-insensitive proximal convoluted tubules and possibly other tissues specialised in fluid transport.