Effect of uncoupling NO/cGMP pathways on carbachol- and CCK-stimulated Ca 2+ entry and amylase secretion from the rat pancreas

Abstract

 Nitric oxide (NO) production reportedly regulates guanosine 3′,5′-cyclic monophosphate (cGMP) formation and Ca 2+ influx in pancreatic acini. We have investigated the functional roles of the NO/cGMP messenger system in rat pancreatic acini. In dispersed acini, the levels of amylase secretion, cytosolic [Ca 2+ ]([Ca 2+ ] i ), NO synthase, and cGMP were measured. The NO synthase inhibitor N G -nitro- L -arginine methyl ester ( L -NAME, 0.01–100 μM) had no effect on amylase secretion induced by various concentrations of carbachol, cholecystokinin octapeptide (CCK-8) or the high affinity CCK agonist, JMV-180. Similarly, L -NAME up to 100 μM did not affect the changes in Ca 2+ spiking evoked by these secretagogues; nor was Ca 2+ entry, refilling or oscillation altered by L -NAME. Sub- and supramaximal concentrations of these secretagogues did not change NO synthase activities compared with basal levels. While sodium nitroprusside (SNP), a NO donor, caused a 9.4-fold increase in cGMP levels compared with basal levels, carbachol, CCK-8 and JMV-180 had no effect. In addition, the guanylate cyclase inhibitor LY 83583 (10 nM to 10 μM) altered neither amylase secretion nor Ca 2+ signaling induced by these secretagogues. These findings indicate that the stimulatory action of carbachol or CCK-8 is not mediated by NO or cGMP. To investigate whether cGMP stimulates pancreatic secretion we showed that both SNP and a cell-permeant cGMP analog at 0.1–1 mM stimulated amylase secretion and Ca 2+ transients to a level equal to 10–15% and 13–24%, respectively, of those observed with maximal concentrations of secretagogues. The guanylate cyclase activator guanylin (1–10 μM), which increased cGMP levels 2.4-fold compared with basal levels, elicited a small amount of amylase secretion and a small Ca 2+ transient. In conclusion, exogenous NO is capable of increasing endogenous cGMP, which results in a modest increase in the [Ca 2+ ] i transient and pancreatic amylase secretion. However, the NO/cGMP system does not appear to be involved significantly in the mediation of Ca 2+ signaling and amylase secretion stimulated by carbachol and CCK-8.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42243/1/424-434-1-25_74340025.pd