Screening of a rat adrenal cDNA library identified a second subtype of the type I angiotensin II receptor, AT1B, which shares 96% amino acid identity with AT1A and has similar ligand binding.
The identification of two subtypes of the rat type I angiotensin II receptor (AT1A and AT1B) provides a molecular basis that might explain the diverse actions of angiotensin II in various tissues.
A rat adrenal cDNA library was screened by colony hybridization using a rat cDNA fragment of type I angiotensin II receptor (AT1A) previously isolated from the kidney. Two cDNA clones were identified, designated as AT1B, to have a nucleotide sequence highly homologous to and yet distinct from AT1A. The amino acid sequence of AT1B consists of 359 amino acid residues and has 96% identity with AT1A. No conspicuous difference in the ligand binding characteristics was observed between AT1A and AT1B. The mRNA for AT1B was expressed in many tissues as is the case with AT1A, and most abundantly expressed in the adrenal glands in the Sprague-Dawley rats. The existence of two subtypes in the rat type I angiotensin II receptor might explain the diverse actions of angiotensin II in various tissues.
Iwai et al. (1992) studied this question. Screening of a rat adrenal cDNA library identified a second subtype of the type I angiotensin II receptor, AT1B, which shares 96% amino acid identity with AT1A and has similar ligand binding.