Cyclic AMP-Sensitive Chloride Efflux in Rabbit Pancreatic Acini

Abstract

ABSTRACT: We studied chloride efflux from isolated rabbit pancreatic acini in suspension, by loading with ³⁶Cl to steady state and rapidly washing acini by filtration to determine ³⁶Cl cpm/μg DNA remaining. Linear loss of acinar chloride occurred over 5 min (k = 0.038 ± 0.008 min^-1, n = 5). Forskolin (5 × 10^-5 M) increased the rate of chloride efflux (k = 0.100 ± 0.016 min^-1, n = 5, p < 0.001) 2.6-fold. At 5 min, forskolin increased acinar cAMP levels (1065 ± 254 versus 7 ± 2 pmol/mL, n = 5, p < 0.005) and percentage of chloride efflux (37.4 ± 2.3 versus 26.0 ± 2.2%, n = 13, p < 0.005). The chloride channel inhibitor anthracene-9-carboxylic acid (10^-3 M) had no effect on chloride loss from acini exposed to vehicle (30.9 ± 1.9 versus 29.9 ± 2.3%, n = 4), but completely inhibited forskolin-stimulated efflux at 5 min (40.0 ± 2.4 versus 29.3 ± 2.4%, n 5, p, < 0.005). Manipulation of extracellular calcium concentration demonstrated that chloride efflux was not coupled to zymogen granule amylase release. Secretin (10^-7 M) increased acinar cAMP levels (68 ± 22 versus 7± 2 pmol/mL, n = 5, p < 0.05) and significantly increased the loss of chloride from acini (34.9 ± 1.4 versus 26.1 ± 1.7%, n = 7, p < 0.005) without affecting amylase release. Secretagogue-stimulated amylase release by cholecystokinin octapeptide (10^-8 M) and carbamylcholine (10^-5 M), did not increase chloride efflux at 5 min. Our findings demonstrate that pancreatic acini possess a chloride efflux pathway that is conductive, cAMP responsive, and distinct from zymogen granule membrane conductance.