REGULATION OF FLUID SECRETION AND INTRACELLULAR MESSENGERS IN ISOLATED RAT PANCREATIC DUCTS BY ACETYLCHOLINE

1. We have studied the effects of acetylcholine (ACh) on fluid secreti on and intracellular messengers in interlobular ducts isolated from th e rat pancreas and maintained in short-term tissue culture. 2. Ductal fluid secretion was measured using micropuncture techniques. Intracell ular free calcium ([Ca2+]i) and cyclic AMP concentrations were measure d in single ducts using fura-2 microspectrofluorimetry and radioimmuno assay techniques respectively. Changes in the levels of these intracel lular messengers were correlated with fluid secretion. 3. ACh stimulat ed ductal fluid secretion. The dose required for a half-maximal respon se was about 0.4 muM and maximal secretion was achieved with 10 muM AC h. These effects of ACh were blocked by atropine and by removal of ext racellular Ca2+. 4. ACh was about four orders of magnitude less potent as an activator of ductal fluid transport than the hormone secretin; however, the maximal rates of fluid secretion evoked by these two agon ists were similar. 5. ACh caused a dose-dependent rise in duct cell [C a2+]i, but had no effect on cyclic AMP. In contrast, secretin increase d duct cell cyclic AMP, but had no effect on [Ca2+]i. 6. The [Ca2+]i r esponse evoked by ACh resulted from both mobilization of intracellular Ca2+ stores and influx of Ca2+ from the extracellular space. 7. The C a2+ ionophore, ionomycin, mimicked the effect of ACh on ductal [Ca]i a nd fluid secretion. 8. We conclude that ACh stimulates fluid secretion from rat pancreatic duct cells by activating a 'Ca2+ pathway' which i s distinct from the well documented 'cyclic AMP pathway utilized by se cretin.