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 (K-d = 0.73 +/- 0.06 nM; B-max = 292 +/- 15 fmol/mg protein, n = 3). Competition studies established that these cells, similar to the intact pancreas, express predominantly the AT(2) receptor subtype. The AT(2)-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 AT(1)-selective antagonist DuP 753 (Losartan). Affinity labeling of these binding sites with [I-125]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 AT(2) antagonist, but not the AT(1) 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 AT(1) antagonist DuP 753 completely inhibited the angiotensin II-induced rise in Ca2+; however, the AT(2) antagonists CGP 42112A and PD 123177 were ineffective in blocking the Ca2+ increase. These results demonstrate that this pancreatic acinar cell line expresses both AT(2) and AT(1) angiotensin II receptor subtypes. The AT(1) receptor is coupled to the mobilization of Ca2+-a characteristic shared by AT(?)1 receptors in other tissues.