Effect of uncoupling NO/cGMP pathways on carbachol- and CCK-stimulated Ca2+ entry and amylase secretion from the rat pancreas.
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.
Yoshida
H
H
3912 Taubman Center, Box 0362, The University of Michigan, Ann Arbor, MI 48109, USA.
Tsunoda
Y
Y
Owyang
C
C
D000681:Amylases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D006152:Cyclic GMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012844:Sincalide / Q000494:pharmacology
D009569:Nitric Oxide; D002217:Carbachol; D000681:Amylases; D006152:Cyclic GMP; D012844:Sincalide; D002118:Calcium