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 Ca2+ 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 [Ca2+]([Ca2+]i), NO synthase, and cGMP were measured. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 0.01-100 microM) 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 microM did not affect the changes in Ca2+ spiking evoked by these secretagogues; nor was Ca2+ 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 microM) altered neither amylase secretion nor Ca2+ 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 Ca2+ 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 microM), which increased cGMP levels 2.4-fold compared with basal levels, elicited a small amount of amylase secretion and a small Ca2+ transient. In conclusion, exogenous NO is capable of increasing endogenous cGMP, which results in a modest increase in the [Ca2+]i transient and pancreatic amylase secretion. However, the NO/cGMP system does not appear to be involved significantly in the mediation of Ca2+ signaling and amylase secretion stimulated by carbachol and CCK-8.

Ascorbic acid acts as an inhibitory transmitter in the hypothalamus to inhibit stimulated luteinizing hormone-releasing hormone release by scavenging nitric oxide

“…We postulate that cGMP would increase intracellular free [Ca 2ϩ ] (18,33). Indeed, increased Ca 2ϩ has been demonstrated in pancreatic acinar cells after NO activation of guanylyl cyclase (36,37). The increased intracellular free Ca 2ϩ would then participate in exocytosis of LH-RH secretory granules.…”

cGMP modulation of ACh-stimulated exocytosis in guinea pig antral mucous cells

“…As mentioned above, the NO/cGMP pathway protects cells from damage in many tissues. cGMP also modulates exocytosis in salivary acinar cells, pancreatic acinar cells, HT-29 cells (human colonic mucus-secreting cells), and chromaffin cells (3,12,17,34), leading us to an idea that cGMP may increase mucin exocytosis in antral mucous cells.…”

Free radicals and the pancreatic acinar cells: role in physiology and pathology

“…NOS activity in isolated cell/acini in response to secretagogues was detected using arginine to citrulline conversion (Gukovskaya & Pandol 1994;Wrenn et al 1994;Ahn et al 1998), by evaluating nitrite concentration (Wrenn et al 1994;Ahn et al 1998;Jaworek et al 2000), or cGMP production (Haymovits & Scheele 1976;Gardner & Rottman 1980;Pandol & Schoeffield-Payne 1990;Wrenn et al 1994;Gilon et al 1995;Gukovskaya & Pandol 1995;Xu et al 1997;Yoshida et al 1997;Ahn et al 1998). Leptin receptor (Jaworek et al 2002a) and protease-activated receptor-2 stimulation (Kawabata et al 2002) was also able to generate NO in acinar cells.…”