INTERACTIONS BETWEEN SECRETIN AND ACETYLCHOLINE IN THE REGULATION OF FLUID SECRETION BY ISOLATED RAT PANCREATIC DUCTS

1. Interlobular ducts were isolated from the rat pancreas and maintain ed in short-term tissue culture. Fluid secretion from these isolated d ucts was measured using micropuncture techniques, intracellular calciu m concentration ([Ca2+](i)) by fura-2 microspectrofluorimetry. and cyc lic AMP by radioimmunoassay. 2. Applying secretin and ACh simultaneous ly to ducts caused either a stimulation or an inhibition of fluid secr etion depending on the doses employed. 3. The inhibitory effect of sec retin and ACh could be relieved by atropine, and by tile protein kinas e C (PKC) inhibitors staurosporine and -isoquinolinylsulphonyl)-2-meth yl-piperazine(H-7). 4. Activation of PRC by 12-O-tetradecanoylphorhol- 13-acetate (TPA) and phorbol 12,13-dibutyrate (PDBu) inhibited secreti n-evoked fluid secretion. 5. ACh and TPA also inhibited fluid secretio n stimulated by the adenylate forskolin. 6. Neither secretin nor the P KC activators and inhibitors had any effect on either the increase in [Ca2+](i) evoked by ACh or the increase in intracellular cyclic AMP ev oked by secretin and forskolin. 7. We conclude that the inhibitory eff ect of combined doses of secret in and ACh on ductal fluid secretion i s probably mediated by PKC at a point in the secretory mechanism dista l to the generation of intracellular messengers.