Heterogeneity of cannabinoid ligand-induced modulations in intracellular Ca₂₊ signals of mouse pancreatic acinar cells in vitro

We recently reported that a CB₂R agonist, GW405833 (GW), reduced both the ACh-induced Ca²⁺ oscillations and the L-arginineinduced Ca²⁺ signal enhancement in mouse pancreatic acinar cells, suggesting that GW-induced inhibition may prevent the pathogenesis of acute pancreatitis. In this study, we aim to evaluate the effects of other cannabinoid ligands on Ca²⁺ signaling in acinar cells. Patch-clamp whole-cell recordings were applied to measure ACh-induced intracellular Ca²⁺ oscillations in pancreatic acinar cells acutely dissociated from wild-type (WT), CB₁R knockout (KO), and CB₂R KO mice, and the pharmacological effects of various cannabinoid ligands on the Ca²⁺ oscillations were examined. We found that all the 8 CB₂R agonists tested inhibited AChinduced Ca²⁺ oscillations. Among them, GW, JWH133, and GP1a caused potent inhibition with IC₅₀ values of 5.0, 6.7, and 1.2 μmol/L, respectively. In CB₂R KO mice or in the presence of a CB₂R antagonist (AM630), the inhibitory effects of these 3 CB₂R agonists were abolished, suggesting that they acted through the CB₂Rs. The CB₁R agonist ACEA also induced inhibition of Ca²⁺ oscillations that existed in CB₁R KO mice and in the presence of a CB₁R antagonist (AM251), suggesting a non-CB₁R effect. In WT, CB₁R KO, and CB₂R KO mice, a nonselective CBR agonist, WIN55,212-2, inhibited Ca²⁺ oscillations, which was not mediated by CB₁Rs or CB₂Rs. The endogenous cannabinoid substance, 2-arachidonoylglycerol (2-AG), did not show an inhibitory effect on Ca²⁺ oscillations. In conclusion, CB₂R agonists play critical roles in modulating Ca²⁺ signals in mouse pancreatic acinar cells, while other cannabinoid ligands modulate Ca²⁺ oscillations in a heterogeneous manner through a CB receptor or non-CB-receptor mechanism.