Properties of AT1a and AT1b angiotensin receptors expressed in adrenocortical Y-1 cells
Tian, Y.; Baukal, A.J.; Sandberg, K.; Bernstein, K.E.; Balla, T.; Catt, K.J.
American Journal of Physiology 270(5 Pt 1): E831-E839
1996
ISSN/ISBN: 0002-9513 PMID: 8967472 Document Number: 463578
Adrenocortical Y-1 cells were stably transfected with the AT-1a and AT-1b subtypes of the rat angiotensin (ANG) II AT-1 receptor cDNA to study the pharmacological and functional properties of the two receptors. Selected clones of transfected cells expressing the AT-1a or AT-1b receptor subtypes bound the native ligand ANG II and the peptide antagonist (Sar-1,Ile-8)ANG II with similar affinities, but they differed in their relative affinities for the nonpeptide antagonist losartan (half-maximal inhibitory concentration 9.7 and 4.7 nM), ANG III (126 and 33 nM), and the peptide antagonist (Sar-1,Gly-8)ANG II (6.2 and 1.2 nM). Photoaffinity labeling of the expressed receptors revealed a single component of 65 kDa for both receptor subtypes, suggesting that both receptors were glycosylated in a similar manner. The sensitivity of 125I-ANG II binding to AT-1a and AT-1b receptors to guanine nucleotides was unaffected by pertussis toxin treatment. ANG II stimulated the formation of inositol phosphates and increased the level of cytoplasmic Call in both AT-1a- and AT-1b-transfected Y-1 cells. However, ANG II had little effect on forskolin-induced adenosine 3',5'-cyclic monophosphate accumulation, causing only minor inhibition in AT-1a-transfected cells and slight enhancement in AT-1b-transfected cells. These data indicate that AT,, and AT-1b receptors show small but significant differences in their binding pharmacology and, upon activation, are coupled through G-q/G-11 to the phosphoinositide-Ca-2+ signaling pathway. However, neither AT-1a nor AT-1b receptors exhibit coupling to G-i and inhibition of adenylate cyclase when expressed in murine adrenal tumor cells.