DIFFERENTIAL EXPRESSION OF ANGIOTENSIN RECEPTOR 1A AND 1B IN MOUSE

At least two distinct genes (AT(1A) and AT(1B)) encode type 1 angiotensin II (AT(1)) receptors in rodents. Receptor binding and Northern blot analysis have clearly demonstrated the presence of AT(1) receptors and AT(1)-receptor mRNA in many tissues but fail to differentiate which type 1 receptor subtype is expressed. A reverse-transcriptase polymerase chain reaction restriction fragment length polymorphism (RT-PCR-RFLP) assay was developed to differentiate the expressed mRNA by subtype. Expression of AT(1A) was clearly evident in kidney, liver, adrenal gland, ovary, brain, testes, adipose tissue, lung, and heart of adult mice. AT(1B) was absent from most of these tissues but was detectable in brain, testes, and adrenal gland. No significant differences in expression were evident in kidney, liver, brain, lung, or heart from 16.5- or 18.5-gestation-day fetuses, and only AT(1A) was evident in placenta. Expression of AT(1B) was confirmed in adrenal gland, brain, and testes, using a primer set that specifically amplifies only AT(1B) mRNA. Expression of AT(1A) and AT(1B) was also examined in As4.1 cells, a renin-expressing mouse kidney tumoral cell line. Receptor binding and competition assays using AT(1)- and AT(2)-receptor antagonists revealed that only AT(1) receptors are present on the cell surface. Extremely low levels of AT(1)-receptor mRNA was detected by Northern blot, and RT-PCR-RFLP analysis revealed that only the AT(1A) subtype is expressed in this cell line. Despite the high homology between the coding sequence of the AT(1A) and AT(1B) genes, they exhibit disparate tissue-specific expression profiles.