Heterogeneity of cannabinoid ligand-induced modulations in intracellular Ca ²⁺ signals of mouse pancreatic acinar cells in vitro

We recently reported that a CB ₂ R agonist, GW405833 (GW), reduced both the ACh-induced Ca ²⁺ oscillations and the L-arginine-induced Ca ²⁺ 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 Ca ²⁺ signaling in acinar cells. Patch-clamp whole-cell recordings were applied to measure ACh-induced intracellular Ca ²⁺ oscillations in pancreatic acinar cells acutely dissociated from wild-type (WT), CB ₁ R knockout (KO), and CB ₂ R KO mice, and the pharmacological effects of various cannabinoid ligands on the Ca ²⁺ oscillations were examined. We found that all the 8 CB ₂ R agonists tested inhibited ACh-induced Ca ²⁺ oscillations. Among them, GW, JWH133, and GP1a caused potent inhibition with IC ₅₀ values of 5.0, 6.7, and 1.2 μmol/L, respectively. In CB ₂ R KO mice or in the presence of a CB ₂ R antagonist (AM630), the inhibitory effects of these 3 CB ₂ R agonists were abolished, suggesting that they acted through the CB ₂ Rs. The CB ₁ R agonist ACEA also induced inhibition of Ca ²⁺ oscillations that existed in CB ₁ R KO mice and in the presence of a CB ₁ R antagonist (AM251), suggesting a non-CB ₁ R effect. In WT, CB ₁ R KO, and CB ₂ R KO mice, a nonselective CBR agonist, WIN55,212-2, inhibited Ca ²⁺ oscillations, which was not mediated by CB ₁ Rs or CB ₂ Rs. The endogenous cannabinoid substance, 2-arachidonoylglycerol (2-AG), did not show an inhibitory effect on Ca ²⁺ oscillations. In conclusion, CB ₂ R agonists play critical roles in modulating Ca ²⁺ signals in mouse pancreatic acinar cells, while other cannabinoid ligands modulate Ca ²⁺ oscillations in a heterogeneous manner through a CB receptor or non-CB-receptor mechanism.