Characterization of angiotensin II receptor subtypes in pancreatic acinar AR42J cells.
The AR42J acinar cell line was characterized as a potential cellular model to assess the functional aspects of an exocrine pancreatic angiotensin system. Binding studies revealed that the AR42J cells express high affinity angiotensin II binding sites (Kd = 0.73 +/- 0.06 nM; Bmax = 292 +/- 15 fmol/mg protein, n = 3). Competition studies established that these cells, similar to the intact pancreas, express predominantly the AT2 receptor subtype. The AT2-selective antagonists CGP 42112A, PD 123177, and PD 123319 competed for the majority of angiotensin II binding. However, 10-15% of the angiotensin II binding sites were competed for by the AT1-selective antagonist DuP 753 (Losartan). Affinity labeling of these binding sites with [125I]angiotensin II followed by SDS gel electrophoresis under reducing conditions revealed a single band comprising a molecular mass of 108,000 Da. Competition with unlabeled angiotensin II or the AT2 antagonist, but not the AT1 antagonist, abolished the 108,000-Da band. In intact cells, angiotensin II caused a rapid increase in intracellular calcium (Ca2+) using Fura-2 as a Ca2+ indicator. Pretreatment of the cells with the AT1 antagonist DuP 753 completely inhibited the angiotensin II-induced rise in Ca2+; however, the AT2 antagonists CGP 42112A and PD 123177 were ineffective in blocking the Ca2+ increase. These results demonstrate that this pancreatic acinar cell line expresses both AT2 and AT1 angiotensin II receptor subtypes. The AT1 receptor is coupled to the mobilization of Ca(2+)--a characteristic shared by AT1 receptors in other tissues.
D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D008954:Models, Biological; D010179:Pancreas / Q000737:chemistry* / Q000166:cytology; D051381:Rats; D011945:Receptors, Angiotensin / Q000032:analysis*; D014407:Tumor Cells, Cultured
D011945:Receptors, Angiotensin; D002118:Calcium