Arachidonic acid modulates the spatiotemporal characteristics of agonist-evoked Ca2+ waves in mouse pancreatic acinar cells

In pancreatic acinar cells analysis of the propagation speed of secretagogu e-evoked Ca2+ waves can be used to examine coupling of hormone receptors to intracellular signal cascades that cause activation of protein kinase C or production of arachidonic acid (AA), In the present study we have investig ated the role of cytosolic phospholipase A(2) (cPLA(2)) and AA in acetylcho line (ACh)- and bombesin-induced Ca2+ signaling. Inhibition of cPLA(2) caus ed acceleration of ACh-induced Ca2+ waves, whereas bombesin-evoked Ca2+ wav es were unaffected. When enzymatic metabolization of AA was prevented with the cyclooxygenase inhibitor indomethacin or the lipoxygenase inhibitor nor dihydroguaiaretic acid, ACh-induced Ca2+ waves were slowed down. Agonist-in duced activation of cPLA(2) involves mitogen-activated protein kinase (MAPK ) activation. An increase in phosphorylation of p38(MAPK) and p42/44(MAPK) within 10 a after stimulation could be demonstrated for ACh but was absent for bombesin, Rapid phosphorylation of p38(MAPK) and p42/44MAPK could also be observed in the presence of cholecystokinin (CCK), which also causes act ivation of cPLA(2). ACh-and CCK-induced Ca2+ waves were slowed down when p3 8MAPK Wag inhibited with SE 203580, whereas inhibition of p42/44MAPK With P D 98059 caused acceleration of ACh- and CCK-induced Ca2+ waves. The spreadi ng of bombesin-evoked Ca2+ waves was affected neither by PD 98059 nor by SE 203580. Our data indicate that in mouse pancreatic acinar cells both ACh a nd CCK receptors couple to the cPLA(2) pathway. cPLA(2) activation occurs w ithin 1-2 s after hormone application and is promoted by p42/44MAPK and inh ibited by p38MAPK. Furthermore, the data demonstrate that secondary (Ca2+-i nduced) Ca2+ release, which supports Ca2+ wave spreading, is inhibited by A A. itself and not by a metabolite of AA.