The 7315c cell, derived from a rat anterior pituitary tumor, expresses an angiotensin II (AII) receptor. [3H]AII binds to 7315c membranes specifically and saturably (K(D) = 2.1 ± 0.6 x 10-9 M, B(max) = 282 ± 33 fmol/mg of protein). GTP diminished the affinity of the membranes for [3H]AII (K(D) = 4.1 ± 0.4 x 10-9 M, B(max) = 210 ± 26 fmol/mg of protein). [3H]AII binding was displaced by AII (K(i) = 1.3 ± 0.6 x 10-9 M), angiotensin III (AIII) (K(i) = 0.9 ± 0.4 x 10-9 M), and the nonpeptide AII antagonist DuP753 (K(i) = 1.4 ± 0.6 x 10-8 M). In contrast, a second nonpeptide AII ligand, PD123177, did not compete for [3H]AII binding sites. In intact cells, AII and AIII stimulated inositol trisphosphate (IP3) production (EC50 = 1.1 ± 0.6 x 10-8 M and 1.1 ± 0.5 x 10-8 M, respectively); this response to AII was antagonized by DuP753 (K(i) = 1.7 ± 0.3 x 10-7 M). Pertussis toxin treatment failed to affect the ability of AII to stimulate IP3 production. In a crude membrane preparation, GTP was required for maximal AII-induced IP3 stimulation; guanosine thio-diphosphate abolished the agonist-GTP stimulation of IP3 production, in a concentration-dependent fashion. AII and AIII also inhibited adenylyl cyclase (EC50 = 2.9 ± 1.1 x 10-8 M and 6.0 ± 1.0 x 10-8 M, respectively). DuP753 antagonized the inhibition by AII of adenylyl cyclase (K(i) = 2.8 ± 0.4 x 10-8 M). PD123177 failed to antagonize AII-induced cyclase inhibition. Pertussis toxin treatment abolished the AII and AIII inhibition of adenylyl cyclase. GTP was required for AII-induced inhibition of adenylyl cyclase. These data suggest that, in 7315c cells, a single subtype of AII receptor, identified by DuP753, is capable of regulating two different guanine nucleotide-binding protein (G protein) signalling pathways; one G protein, which is insensitive to pertussis toxin, stimulates IP3 production and the other G protein, which is sensitive to pertussis toxin, inhibits adenylyl cyclase.
|Original language||English (US)|
|Number of pages||9|
|State||Published - 1992|
ASJC Scopus subject areas
- Molecular Medicine