Congo red modulates ACh-induced Ca(2+) oscillations in single pancreatic acinar cells of mice

Endogenous Amyloid-formed Ca2+-permeable Channels in Aged 3xTg AD Mice

Alzheimer's disease (AD), the leading cause of dementia, is characterized by the accumulation of beta-amyloid peptides (Aβ). However, whether Aβ itself is a key toxic agent in AD pathogenesis and the precise mechanism of Aβ-elicited neurotoxicity are still debated. Emerging evidence demonstrates that the Aβ channel/pore hypothesis could explain Aβ toxicity, because Aβ oligomers are able to disrupt membranes and cause edge-conductivity pores that may disrupt cell Ca2+ homeostasis and drive neurotoxicity in AD. However, all available data to support this hypothesis have been collected from "in vitro" experiments using high concentrations of exogenous Aβ. It is still unknown whether Aβ channels can be formed by endogenous Aβ in AD animal models. Here, we report an unexpected finding of the spontaneous Ca2+ oscillations in aged 3xTg AD mice but not in age-matched wild-type mice. These spontaneous Ca2+ oscillations are sensitive to extracellular Ca2+, ZnCl2, and the Aβ channel blocker Anle138b, suggesting that these spontaneous Ca2+ oscillations in aged 3xTg AD mice are mediated by endogenous Aβ-formed channels.

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-arginine-induced 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 ACh-induced 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.

The 2-aminoethoxydiphenyl borate analog, DPB161 blocks store-operated Ca2+ entry in acutely dissociated rat submandibular cells

Cellular Ca²⁺ signals play a critical role in cell physiology and pathology. In most non-excitable cells, store-operated Ca²⁺ entry (SOCE) is an important mechanism by which intracellular Ca²⁺ signaling is regulated. However, few drugs can selectively modulate SOCE. 2-Aminoethoxydiphenyl borate (2APB) and its analogs (DPB162 and DPB163) have been reported to inhibit SOCE. Here, we examined the effects of another 2-APB analog, DPB161 on SOCE in acutely-isolated rat submandibular cells. Both patch-clamp recordings and Ca²⁺ imaging showed that upon removal of extracellular Ca²⁺ ([Ca²⁺]_o=0), rat submandibular cells were unable to maintain ACh-induced Ca²⁺ oscillations, but restoration of [Ca²⁺]_o to refill Ca²⁺ stores enable recovery of these Ca²⁺ oscillations. However, addition of 50 μM DPB161 with [Ca²⁺]_o to extracellular solution prevented the refilling of Ca²⁺ store. Fura-2 Ca²⁺ imaging showed that DPB161 inhibited SOCE in a concentration-dependent manner. After depleting Ca²⁺ stores by thapsigargin treatment, bath perfusion of 1 mM Ca²⁺ induced [Ca²⁺]_i elevation in a manner that was prevented by DPB161. Collectively, these results show that the 2-APB analog DPB161 blocks SOCE in rat submandibular cells, suggesting that this compound can be developed as a pharmacological tool for the study of SOCE function and as a new therapeutic agent for treating SOCE-associated disorders.

Cannabinoid receptor subtype 2 (CB2R) agonist, GW405833 reduces agonist-induced Ca(2+) oscillations in mouse pancreatic acinar cells

Emerging evidence demonstrates that the blockade of intracellular Ca(2+) signals may protect pancreatic acinar cells against Ca(2+) overload, intracellular protease activation, and necrosis. The activation of cannabinoid receptor subtype 2 (CB2R) prevents acinar cell pathogenesis in animal models of acute pancreatitis. However, whether CB2Rs modulate intracellular Ca(2+) signals in pancreatic acinar cells is largely unknown. We evaluated the roles of CB2R agonist, GW405833 (GW) in agonist-induced Ca(2+) oscillations in pancreatic acinar cells using multiple experimental approaches with acute dissociated pancreatic acinar cells prepared from wild type, CB1R-knockout (KO), and CB2R-KO mice. Immunohistochemical labeling revealed that CB2R protein was expressed in mouse pancreatic acinar cells. Electrophysiological experiments showed that activation of CB2Rs by GW reduced acetylcholine (ACh)-, but not cholecystokinin (CCK)-induced Ca(2+) oscillations in a concentration-dependent manner; this inhibition was prevented by a selective CB2R antagonist, AM630, or was absent in CB2R-KO but not CB1R-KO mice. In addition, GW eliminated L-arginine-induced enhancement of Ca(2+) oscillations, pancreatic amylase, and pulmonary myeloperoxidase. Collectively, we provide novel evidence that activation of CB2Rs eliminates ACh-induced Ca(2+) oscillations and L-arginine-induced enhancement of Ca(2+) signaling in mouse pancreatic acinar cells, which suggests a potential cellular mechanism of CB2R-mediated protection in acute pancreatitis.