Angiotensin II-mediated signal transduction events in cystic fibrosis pancreatic duct cells

Abstract

Different signal transduction pathways, i.e. Ca 2+- and cAMP-dependent, involved in mediating the effects of angiotensin II (AII) were investigated separately using the short-circuit current ( I sc) technique and radioimmunoassay (RIA) in a cystic fibrosis pancreatic cell line (CFPAC-1) which exhibits defective cAMP-dependent but intact Ca 2+-dependent anion secretion. The AII-induced I sc could be inhibited by the specific antagonist for AT 1, losartan (1 μM), but not the antagonist for AT 2, PD123177 (up to 10 μM). The AII-induced I sc was also reduced by the treatment of the cells with a Ca 2+ chelator, BAPTA-AM (100 μM), indicating a dependence of the AII-induced anion secretion on the intracellular Ca 2+. Treatment of the cells with pertussis toxin (0.1 μg/ml) or a phospholipase C (PLC) inhibitor, U73122 (5 μM), resulted in a substantial reduction in the AII-induced I sc indicating involvement of Gi and PLC in the Ca 2+-dependent anion secretion. RIA measurements showed that AII stimulated an increase in cAMP production which could be reduced by losartan, pertussis toxin and U73122 but not BAPTA-AM. In addition, inhibitors of cyclooxygenase, indomethacin (10 μM) and piroxicam (10 μM), did not have any effect on the AII-induced cAMP production, excluding the involvement of prostaglandins. Our results suggest that both AII-stimulated cAMP and Ca 2+-dependent responses are mediated by the AT 1 receptor and Gi-coupled PLC pathway. However, the AII-stimulated cAMP production in CFPAC-1 cells is not dependent on Ca 2+ or the formation of prostaglandins.