Interactions of intracellular mediators of amylase secretion in permeabilized pancreatic acini

Mouse pancreatic acini were permeabilized with streptolysin O to investigate amylase secretion stimulated by various intracellular mediators and the kinetics of secretion as a function of temperature. Amylase secretion was temperature dependent in that the initial rate of Ca2+-stimulated secretion increased with increasing temperature. In addition, there was no enhancement of Ca2+-stimulated secretion by GTP[[gamma]S] at 14[deg]C, while enhancement was maximal at 30[deg]C. GTP[[gamma]S]-mediated enhancement of secretion at a given temperature was mostly due to sustained secretion with a small increase in secretory rate. At 30[deg]C Ca2+-stimulated secretion was also enhanced by cAMP and phorbol ester (TPA) to similar extents as by GTP[[gamma]S]. The maximally effective concentration of cAMP was 1-10 [mu]M in the presence of 0.1 mM isobutylmethylxanthine. The enhancements of Ca2+-stimulated amylase secretion by all combinations of cAMP (100 [mu]M plus 0.1 mM isobutylmethylxanthine), TPA (1 [mu]M), and GTP[[gamma]S] (30 [mu]M) were fully additive. In Ca2+-free buffer, cAMP, TPA or GTP[[gamma]S] individually had no effect on amylase secretion. Together, TPA and GTP[[gamma]S] stimulated Ca2+-independent secretion, which was 187 +/- 38% of basal. Cyclic AMP together with TPA and GTP[[gamma]S] in the absence of Ca2+ stimulated 329 +/- 30% of basal secretion. Ca2+-stimulated amylase secretion was decreased about 50% by metabolic inhibition, while the enhancement by cAMP, TPA or GTP[[gamma]S] was totally blocked by metabolic inhibitors. These data demonstrate that amylase secretion in the acinar cell is mediated by multiple intracellular pathways which act in parallel and probably converge at a distal step in the exocytotic process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29498/1/0000584.pd

5-hydroxytryptamine strongly inhibits fluid secretion in guinea pig pancreatic duct cells

We studied the distribution of 5-hydroxytryptamine– (5-HT-) containing cells in the guinea pig pancreas and examined the effects of 5-HT on fluid secretion by interlobular pancreatic ducts. The 5-HT–immunoreactive cells with morphological characteristics of enterochromaffin (EC) cells were scattered throughout the duct system and were enriched in islets of Langerhans. The fluid secretory rate in the isolated interlobular ducts was measured by videomicroscopy. Basolateral applications of 5-HT strongly but reversibly reduced HCO(3)-dependent, as well as secretin- and acetylcholine- (ACh-) stimulated, fluid secretion, whereas 5-HT applied into the lumen had no such effects. Secretin-stimulated fluid secretion could be inhibited by a 5-HT(3) receptor agonist, but not by agonists of the 5-HT(1), 5-HT(2), or 5-HT(4) receptors. Under the stimulation with secretin, 5-HT decreased the intracellular pH (pH(i)) and reduced the rate of pH(i) recovery after acid loading with NH(4)(+), suggesting that 5-HT inhibits the intracellular accumulation of HCO(3)(–). The elevation of intraductal pressure in vivo reduced secretin-stimulated fluid secretion, an effect that could be attenuated by a 5-HT(3) receptor antagonist. Thus, 5-HT, acting through basolateral 5-HT(3) receptors, strongly inhibits spontaneous, secretin-, and ACh-stimulated fluid secretion by guinea pig pancreatic ducts. 5-HT released from pancreatic ductal EC cells on elevation of the intraductal pressure may regulate fluid secretion of neighboring duct cells in a paracrine fashion

Ethanol induces fluid hypersecretion from guinea-pig pancreatic duct cells

Ethanol is the leading cause of pancreatitis; however, its cellular effects are poorly understood. We examined the direct effects of ethanol in the concentration range 0.1–30 mM, i.e. relevant to usual levels of drinking, on fluid secretion from guinea-pig pancreatic duct cells. Fluid secretion was continuously measured by monitoring the luminal volume of interlobular duct segments isolated from the guinea-pig pancreas. [Ca2+]i was estimated by microfluorometry in duct cells loaded with fura-2. Ethanol at 0.3–30 mM significantly augmented fluid secretion stimulated by physiological (1 pM) or pharmacological (1 nM) concentrations of secretin. It augmented dibutyryl cAMP-stimulated fluid secretion but failed to affect spontaneous or acethylcholine-stimulated secretion. Ethanol at 1 mM shifted the secretin concentration-fluid secretion response curve upwards and raised the maximal secretory response significantly by 41 %. In secretin-stimulated ducts, 1 mM ethanol induced a transient increase in [Ca2+]i that was dependent on the presence of extracellular Ca2+. Ethanol failed to augment secretin-stimulated secretion from ducts pretreated with an intracellular Ca2+ buffer (BAPTA) or a protein kinase A inhibitor (H89). In conclusion, low concentrations of ethanol directly augment pancreatic ductal fluid secretion stimulated by physiological and pharmacological concentrations of secretin, and this appears to be mediated by the activation of both the intracellular cAMP pathway and Ca2+ mobilization