ACh-induced Ca2 Research Articles

The Antiproteinopathy, Antioxidant, and Antiapoptotic Effects of Methylene Blue and 4-Phenylbutyric Acid Alone, and in Combination on Familial Alzheimer's Disease PSEN1 I416T Cholinergic-Like Neurons.

Familial Alzheimer's disease (FAD) is a chronic neurological condition that progresses over time. Currently, lacking a viable treatment, the use of multitarget medication combinations has generated interest as a potential FAD therapy approach. In this study, we examined the effects of 4-phenylbutyric acid (4-PBA) and methylene blue (MB) either separately or in combination on PSEN1 I416T cholinergic-like neuron cells (ChLNs), which serve as a model for FAD. We found that MB was significantly efficient at reducing the accumulation of intracellular Aβ, phosphorylation of TAU Ser202/Thr205, and increasing Δψm, whereas 4-PBA was significantly efficient at diminishing oxidation of DJ-1Cys106-SH, expression of TP53, and increasing ACh-induced Ca2+ influx. Both agents were equally effective at blunting phosphorylated c-JUN at Ser63/Ser73 and activating caspase 3 (CASP3) into cleaved caspase 3 (CC3) on mutant cells. Combination of MB and 4-PBA at middle (0.1, 1) concentration significantly reduced iAβ, p-TAU, and oxDJ-1 and augmented the ACh-induced Ca2+ influx compared to combined agents at low (0.05, 0.5) or high (0.5, 5) concentration. However, combined MB and 4-PBA were efficient only at dropping DJ-1Cys106-SO3 and increasing ACh-induced Ca2+ inward in mutant ChLNs. Our data show that the reagents MB and 4-PBA alone possess more than one action (e.g., antiamyloid, antioxidant, anti-TAU, antiapoptotic, and ACh-induced Ca2+ influx enhancers), that in combination might cancel or diminish each other. Together, these results strongly argue that MB and 4-PBA might protect PSEN1 I416T ChLNs from Aβ-induced toxicity by working intracellularly as anti-Aβ and anti-Tau agents, improving Δψm and cell survival, and extracellularly, by increasing ACh-induced Ca2+ ion influx. MB and 4-PBA are promising drugs with potential for repurposing in familial AD.

Minocycline mitigates Aβ and TAU pathology, neuronal dysfunction, and death in the PSEN1 E280A cholinergic-like neurons model of familial Alzheimer’s disease

Familial Alzheimer’s disease (FAD) presenilin 1 E280A (PSEN1 E280A) is a severe neurological condition due to the loss of cholinergic neurons (ChNs), accumulation of amyloid beta (Aβ), and abnormal phosphorylation of the TAU protein. Up to date, there are no effective therapies available. The need for innovative treatments for this illness is critical. We found that minocycline (MC, 5 μM) was innocuous toward wild-type (WT) PSEN1 ChLNs but significantly (i) reduces the accumulation of intracellular Aβ by −69%, (ii) blocks both abnormal phosphorylation of the protein TAU at residue Ser202/Thr205 by −33% and (iii) phosphorylation of the proapoptotic transcription factor c-JUN at residue Ser63/Ser73 by −25%, (iv) diminishes oxidized DJ-1 at Cys106-SO3 by −29%, (v) downregulates the expression of transcription factor TP53, (vi) BH-3-only protein PUMA, and (vii) cleaved caspase 3 (CC3) by −33, −86, and −78%, respectively, compared with untreated PSEN1 E280A ChLNs. Additionally, MC increases the response to ACh-induced Ca2+ influx by +92% in mutant ChLNs. Oxygen radical absorbance capacity (ORAC) and ferric ion-reducing antioxidant power (FRAP) analysis showed that MC might operate more efficiently as a hydrogen atom transfer agent than a single electron transfer agent. In silico molecular docking analysis predicts that MC binds with high affinity to Aβ (Vina Score −6.6 kcal/mol), TAU (VS -6.5 kcal/mol), and caspase 3 (VS -7.1 kcal/mol). Taken together, our findings suggest that MC demonstrates antioxidant, anti-amyloid, and anti-apoptosis activity and promotes physiological ACh-induced Ca2+ influx in PSEN1 E280A ChLNs. The MC has therapeutic potential for treating early-onset FAD.

Cellular Model for the Analysis of IRBIT-Dependent Regulation of the Type 1 IP<sub>3</sub> Receptor

In vertebrate genomes, three genes encode subunits of IP3 receptors, including IP3R1, IP3R2, and IP3R3. Despite high homology between different subunits, homotetrameric IP3 receptors formed by IP3R1, IP3R2, and IP₃R3 in the endoplasmic reticulum membrane are markedly distinct by their functional features and regulatory mechanisms. It was particularly reported that IP3R1 is specifically regulated by the IP3R binding protein released with IP₃ (IRBIT), which competes with IP3 for binding to IP3R1. In turn, affinity of IRBIT/IP₃R1 binding is regulated by phosphorylation of IRBIT. By using the CRISPR/Cas9 approach to edit the genome of HEK-293 cells, two monoclonal cell lines were generated as a platform for uncovering a role of IRBIT and associated regulatory circuits in control of the IP₃R1 activity. In one line, HEK-IP3R1, IP₃R2, and IP3R3 genes were disrupted, while IP₃R1 was remained functional. Based on this line, the HEK-IP3R1/DIRBIT line was generated, wherein IRBIT (AHCYL1) gene was inactivated. The comparative analysis of ACh-induced Ca2+ signaling in cells of both lines was performed by employing the Ca2+ dye Fluo-4 and Ca2+ imaging. It was particularly shown that ACh mobilized Ca2+ in cells of both lines, which responded to the agonist at widely varied doses in an “all-or-nothing” manner. Yet, HEK-IP₃R1/DIRBIT cells turned out to be less sensitive to ACh compared to HEK-IP₃R1 cells.

Berberine inhibits intracellular Ca2+ signals in mouse pancreatic acinar cells through M3 muscarinic receptors: Novel target, mechanism, and implication

Berberine, a natural isoquinoline alkaloid, exhibits a variety of pharmacological effects, but the pharmacological targets and mechanisms remain elusive. Here, we report a novel finding that berberine inhibits acetylcholine (ACh)-induced intracellular Ca2+ oscillations, mediated through an inhibition of the muscarinic subtype 3 (M3) receptor. Patch-clamp recordings and confocal Ca2+ imaging were applied to acute dissociated pancreatic acinar cells prepared from CD1 mice to examine the effects of berberine on ACh-induced Ca2+ oscillations. Whole-cell patch-clamp recordings showed that berberine (from 0.1 to 10 µM) reduced ACh-induced Ca2+ oscillations in a concentration-dependent manner, and this inhibition also depended on ACh concentrations. The inhibitory effect of berberine neither occurred in intracellular targets nor extracellular cholecystokinin (CCK) receptors, chloride (Cl-) channels, and store-operated Ca2+ channels. Together, the results demonstrate that berberine directly inhibits the muscarinic M3 receptors, further confirmed by evidence of the interaction between berberine and M3 receptors in pancreatic acinar cells.

Combination of Tramiprosate, Curcumin, and SP600125 Reduces the Neuropathological Phenotype in Familial Alzheimer Disease PSEN1 I416T Cholinergic-like Neurons.

Familial Alzheimer's disease (FAD) is a complex and multifactorial neurodegenerative disorder for which no curative therapies are yet available. Indeed, no single medication or intervention has proven fully effective thus far. Therefore, the combination of multitarget agents has been appealing as a potential therapeutic approach against FAD. Here, we investigated the potential of combining tramiprosate (TM), curcumin (CU), and the JNK inhibitor SP600125 (SP) as a treatment for FAD. The study analyzed the individual and combined effects of these two natural agents and this pharmacological inhibitor on the accumulation of intracellular amyloid beta iAβ; hyperphosphorylated protein TAU at Ser202/Thr205; mitochondrial membrane potential (ΔΨm); generation of reactive oxygen species (ROS); oxidized protein DJ-1; proapoptosis proteins p-c-JUN at Ser63/Ser73, TP53, and cleaved caspase 3 (CC3); and deficiency in acetylcholine (ACh)-induced transient Ca2+ influx response in cholinergic-like neurons (ChLNs) bearing the mutation I416T in presenilin 1 (PSEN1 I416T). We found that single doses of TM (50 μM), CU (10 μM), or SP (1 μM) were efficient at reducing some, but not all, pathological markers in PSEN 1 I416T ChLNs, whereas a combination of TM, CU, and SP at a high (50, 10, 1 μM) concentration was efficient in diminishing the iAβ, p-TAU Ser202/Thr205, DJ-1Cys106-SO3, and CC3 markers by -50%, -75%, -86%, and -100%, respectively, in PSEN1 I417T ChLNs. Although combinations at middle (10, 2, 0.2) and low (5, 1, 0.1) concentrations significantly diminished p-TAU Ser202/Thr205, DJ-1Cys106-SO3, and CC3 by -69% and -38%, -100% and -62%, -100% and -62%, respectively, these combinations did not alter the iAβ compared to untreated mutant ChLNs. Moreover, a combination of reagents at H concentration was able to restore the dysfunctional ACh-induced Ca2+ influx response in PSEN 1 I416T. Our data suggest that the use of multitarget agents in combination with anti-amyloid (TM, CU), antioxidant (e.g., CU), and antiapoptotic (TM, CU, SP) actions might be beneficial for reducing iAβ-induced ChLN damage in FAD.

Superoxide Anions Inhibit Intracellular Calcium Response in Porcine Airway Smooth Muscle Cells.

Background Superoxide anions (O 2 - ) have multiple effects on pulmonary parenchyma altering cell proliferation, cellular metabolism, and airway smooth muscle (ASM) contraction. Intracellular calcium ([Ca 2+ ] i ) concentration plays a significant role in the regulation of ASM contraction, relaxation, proliferation, and gene expression. Objective We investigated the effects of O 2 - on agonist-stimulated changes in [Ca 2+ ] i in ASM cells. Design/Methods Fura-2 AM-loaded, freshly isolated porcine ASM (PASM) cells were used to examine [Ca 2+ ] i release in response to acetylcholine (ACh), histamine, endothelin, caffeine, and thapsigargin (TPG) in the presence or absence of extracellular Ca 2+ . Results Exposure of PASM cells to xanthine and xanthine oxidase (X + XO) resulted in a time-dependent generation of O 2 - , inhibited by superoxide dismutase (SOD). Preincubating PASM cells with X + XO for 15- or 45-minute inhibited net [Ca 2+ ] i responses to ACh, histamine, caffeine, and TPG compared with control cells. Pretreating PASM cells with SOD for 30 minutes mitigated the inhibitory effect of X + XO treatment on ACh-induced Ca 2+ elevation suggesting role of O 2 - . X + XO treatment also inhibited caffeine- and TPG-induced Ca 2+ elevation suggesting effect of O 2 - on [Ca 2+ ] i release and reuptake mechanisms. Conclusion Superoxide attenuates [Ca 2+ ] i release, reuptake, and may interfere with physiological functions of ASM cells.

Role of aquaporin 5 and glandular blood flow in the acetylcholine-induced secretion of saliva in rats.

To clarify the role of the aquaporin 5 (AQP5) in salivary secretion, we evaluated acetylcholine (ACh)-induced secretion in Sprague-Dawley (SD) rats, rats expressing a low level of AQP5 protein (AQP5/low SD) which developed from SD rats, and Wistar/ST rats. The salivary secretion in AQP5/low SD rats in response to infusions of low-dose ACh (60-120 nmol/min) was 27-42% of that in SD rats. By contrast, Wistar/ST rats exhibited comparable secretion to that of SD rats in response to low-doses ACh, despite their low-level expression of AQP5. Experiments using spectrofluorometry and RT-PCR demonstrated no differences in the ACh-induced Ca2+ responses or the mRNA expression of muscarinic receptor, Cl- channel, or cotransporter between these strains. These findings imply that factors other than the function of salivary acinar cells regulates the secretion in response to weak stimuli. Monitoring of the hemodynamics in the submandibular gland revealed that low-doses ACh induced different patterns of the fluctuations in the blood flow in these strains. The blood flow decreased below the resting level in AQP5/low SD rats, but remained mostly above the resting level in Wistar/ST rats. The present study reveals that the contribution of AQP5-dependent transport of water is altered by stimulus intensity and blood flow.

Expression and function of umami receptors T1R1/T1R3 in gastric smooth muscle.

l-amino acids, such as monosodium glutamate (MSG), activate the umami receptor T1R1/T1R3. We previously showed increased peristalsis in response to activation of T1R1/T1R3 by MSG in mouse colon. However, the expression and function of these receptors in the different regions of the stomach are not clear. Mouse gastric smooth muscle cells (SMCs) were isolated and cultured in Dulbecco's Modified Eagle Medium. Expression of T1R1 and T1R3 was measured by RT-PCR and Western blot. The effect of MSG with and without inosine monophosphate (IMP, an allosteric activator of T1R1/T1R3) on acetylcholine (ACh)-induced contraction was measured in muscle strips and isolated SMCs by scanning micrometry. The effect of MSG with or without IMP on activation of G proteins and ACh-induced Ca2+ release was measured in SMCs. Monosodium glutamate inhibited ACh-induced contractions in muscle strips from both antrum and fundus and the effect of MSG was augmented by IMP; the effects were concentration-dependent and not affected by the nitric oxide synthase inhibitor, L-NNA, or tetrodotoxin suggesting a direct effect on SMCs. In isolated gastric SMCs, T1R1 and T1R3 transcripts and protein were identified. Addition of MSG with or without IMP inhibited ACh-induced Ca2+ release and muscle contraction; the effect on contraction was blocked by pertussis toxin suggesting activation of Gαi proteins. MSG in the presence of IMP selectively activated Gαi2 . Umami receptors (T1R1/T1R3) are present on SMCs of the stomach, and activation of these receptors induces muscle relaxation by decreasing [Ca2+ ]i via Gαi2 .

Mechanisms of Cannabinoid 2 receptor agonist JWH133-mediated modulations in cell calcium signals of mouse pancreatic acinar cells and its application for treatment of acute pancreatitis

Objective To evaluate the effect of JWH133 on acetylcholine (Ach)-induced Ca2+ oscillations, and to elucidate its mechanism and target. Methods Pancreatic acinar cells were isolated by enzymatic hydrolysis. Patch-clamp whole cell recording techniques were used to measure the effects of 10 μmol/L JWH133 on 10 nmol/L ACh-induced intracellular Ca2+ oscillations in pancreatic acinar cells acutely dissociated from wild-type (WT), and Cannabinoid 2 receptor (CB2R) knockout (KO) mice, and the pharmacological effects of JWH133 on the Ca2+ oscillations. The effect of 10 μmol/L JWH133 on the enhancement of Ca2+ oscillation induced by 10 mmol/L L-Arginine (L-Arg) was measured. The model of acute pancreatitis in mice was induced by L-Arg, and the histological structure, cell morphology and hemorrhagic necrosis were examined. Results The results showed that JWH133 could inhibit ACh-induced Ca2+ oscillations likely through CB2R. Patch-clamp recordings demonstrated that 10 μmol/L of JWH133 could reduce the 10 nmol/L ACh-induced Ca2+ oscillations current to (26.0±4.2)% (P 0.05, n=9). 10 μmol/L of JWH133 attenuated the enhancement of calcium oscillations current to (106.0±16.7)% (P<0.01, n=10) induced by 10 mmol/L L-Arg. In L-Arg acute pancreatitis model, JWH133 improved L-Arg -induced pancreatic pathological changes (P<0.05, n=5). Conclusion JWH133 inhibits intracellular calcium signals by selectively inhibiting extracellular CB2R. In L-Arg -induced acute mouse pancreatitis model, JWH133 significantly improves pathological changes. All these results suggest that JWH133 is a promising candidate for treatment of acute pancreatitis. Key words: Acute pancreatitis; Cannabinoid 2 receptor agonist; Calcium signals; Patch clamp

Stimulation of Muscarinic Receptors Activate Acid Sensing Ion Channel 1 in Isolated Mesenteric Artery Endothelial Tubes

Acid sensing ion channel 1 (ASIC1) belongs to the amiloride‐sensitive degenerin/epithelial sodium channel superfamily and is permeable to both Na+ and Ca2+. ASIC1 is expressed in vascular smooth muscle and/or endothelial cells of various vascular beds and is activated following stimulation of G protein‐coupled receptors (GPCR). In the pulmonary circulation, ASIC1 contributes to GPCR‐induced vasoconstriction and vascular smooth muscle Ca2+ influx via a store‐operated Ca2+ entry (SOCE) mechanism. In small mesenteric arteries, we have recently shown that ASIC1 contributes to acetylcholine (ACh)‐induced vasodilation and endothelial cell Ca2+ entry, however ASIC1‐mediated Ca2+ influx is not SOCE‐dependent in mesenteric artery endothelial cells. Thus, further investigation is needed to understand the mechanism by which ASIC1 is activated by GPCR in small mesenteric artery endothelial cells. Previous studies show ASIC1 is activated by arachidonic acid, therefore we hypothesized that acetylcholine stimulates ASIC1 in mesenteric artery endothelial cells through activation of phospholipase A2 (PLA2) and release of arachidonic acid. To test this hypothesis, we examined endothelial Ca2+ influx via Mn2+ quenching of fura‐2 fluorescence in freshly isolated mesenteric artery endothelial tubes. The PLA inhibitor methyl arachidonyl fluorophosphonate (MAF; 500 nM) attenuated the Ca2+ entry response to ACh, confirming that PLA2‐signaling contributes to the ACh‐induced Ca2+ entry in mesenteric artery endothelial cells. In addition, the selective inhibitor of ASIC1, psalmotoxin 1 (PcTX1; 20 nM), attenuated arachidonic acid‐induced Ca2+‐influx in mesenteric artery endothelial tubes. Although these studies suggest stimulation of muscarinic receptors activate ASIC1 through a PLA2‐arachidonic acid signaling mechanism in mesenteric endothelium, further studies are needed to identify the downstream effector of ASIC1.Support or Funding InformationSupported by National Heart, Lung, and Blood Institute Grants R01 HL‐111084 (to N.L. Jernigan), T32 HL007736 (to T.C. Resta), and American Heart Association Grant 18TPA34110281 (to N.L. Jernigan).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Endothelial cell transient receptor potential channel C5 (TRPC5) is essential for endothelium-dependent contraction in mouse carotid arteries

Augmented endothelium-dependent contractions (EDC) contributes to endothelial dysfunction and vascular disease progression. An early signal in EDC is cytosolic [Ca2+]i rise in endothelial cells, which stimulates the production of contractile prostanoids, leading to vascular contraction. In this study, the molecular identity of Ca2+-permeable channels in endothelial cells and its function were investigated. Vascular tension was measured by wire myograph. EDCs were elicited by acetylcholine (ACH) in the presence of NG-nitro-l-arginine methyl ester (L-NAME). [Ca2+]i was measured using a Ca2+-sensitive fluorescence dye. Enzyme Immunoassay (EIA) was used for prostaglandin measurement. Immunohistochemical staining found the expression of transient receptor potential channel C5 (TRPC5) in endothelial and smooth muscle cells of mouse carotid arteries. ACH-induced EDC in male mouse carotid arteries was found to be substantially reduced in TRPC5 knockout (KO) mice than in wild-type (WT) mice. TRPC5 inhibitors clemizole and ML204 also reduced the EDC. Furthermore, ACH-induced Ca2+ entry in endothelial cells was lower in TRPC5 KO mice than in WT mice. Moreover, the EDC was abolished by a cyclooxygenase-2 (COX-2) inhibitor NS-398, but not affected by a COX-1 inhibitor valeryl salicylate (VAS). Enzyme immunoassay results showed that TRPC5 stimulated the COX-2-linked production of prostaglandin F2α (PGF2α), prostaglandin E2 (PGE2), and prostaglandin D2 (PGD2). Exogeneous PGF2α, PGE2, and PGD2 could induce contractions in carotid arteries. Our present study demonstrated that TRPC5 in endothelial cells contributes to EDC by stimulating the production of COX-2-linked prostanoids. The finding extends our knowledge about EDC.

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.

Mechanism of 2-aminoethoxydiphenylboronic acid in acetylcholine-inducing Ca2+ signals in acute dissociated mouse pancreatic acinar cells

Objective To reveal the mechanism of 2-aminoethoxydiphenyl borate (2APB) modulates intracellular Ca2+ oscillations. Methods Intracellular Ca2+ signals was monitored directly using Ca2+ -dimensional dye (fluo-4) imaging technique in acute dissociated mouse pancreatic acinar cells. The effect and mechanism of 2APB on acetylcholine (Ach)-induced Ca2+ oscillations were examined by patch-clamp whole cell recording. Results (1) 2APB-induced modulations in acinar cell Ca2+ signals were dependent on 2APB concentrations, with increase of 2APB concentrations (1-100 μmol/L), the amplitude and width of Ca2+ oscillations were increased. (2) 2APB enhanced ACh-induced Ca2+ oscillations were also dependent on the concentrations of ACh. When ACh was less than 5 nmol/L, 2APB did not show effect, between ACh 10-30 nmol/L, 2APB potentiated ACh-induced oscillations, while ACh was higher than 100 nmol/L, 2APB inhibited Ca2+ responses. (3) 2APB enhanced ACh-induced Ca2+ oscillations through extracellular rather than intracellular targets because no effect was found by intracellular application of 100 μmol/L 2APB on 10 nmol/L ACh-induced Ca2+ oscillations (P=0.378, n=6); (4) 2APB significantly blocked SOCE, which can reduced the 3 μmol/L TG-induced Ca2+ oscillations current to (3.0±4.8)% (P=0.000, n=6), suggesting that SOCE may be the target of 2APB to enhance Ca2+ oscillations. (5) SOCE blocker GSK can mimic 2APB’s effect to enhance Ca2+ oscillations (P=0.000, n=7). (6) Using thapsigargin to empty Ca2+ pools, the Ca2+ oscillations current become (93.0±9.5)% (P=0.427, n=7) when 2APB added. In other words, 2APB’s effect was eliminated, suggesting that 2APB-induced Ca2+ oscillations is dependent on Ca2+ pool’s conditions. Conclusion At low ACh concentrations (10-30 nmol/L) (where Ca2+ pool is partially emptied and SOCE is open), 2APB blocks SOCC and promotes Ca2+ further release from Ca2+ pool, resulting in Ca2+ oscillation enhancement. Wherease at higher ACh concentrations (>100 nmol/L), 2APB blocks SOCC and prevents Ca2+ pool refilling from extracellular Ca2+ , thus reduces Ca2+ signal response. Key words: 2-aminoethoxydiphenyl borate; Calcium signals; Pancreatic acinar cells; Patch clam

Effects of cannabinoid receptor ligands on acetylcholine-induced calcium oscillations in mouse pancreatic acinar cells

Objective To investigate the effects of various CBR ligands on acetylcholine (Ach) -induced Ca2+ oscillations in acute isolated pancreatic acinar cells. Methods Patch-clamp whole-cell recordings were applied to measure ACh-induced intracellular Ca2+ oscillations in pancreatic acinar cells acutely dissociated from wild-type (WT), cannabinoid type 1 receptor (CB1R) knockout (KO), and cannabinoid type 2 receptor (CB2R) KO mice, and the pharmacological effects of various cannabinoid ligands on the Ca2+ oscillations were examined. Results Patch-clamp recordings demonstrated that all tested three CB2R agonists inhibited intracellular Ca2+ oscillations, 10 μmol/L of GW, GP1a, and JWH133 can reduced the 30 nmol/L ACh-induced Ca2+ oscillations current to (23.0±4.4)% (P=0.000, n=7), (11.0±4.6)% (P=0.000, n=6) and (26.0±4.2)% (P=0.000, n=9) respectively. In CB2R KO mice, the inhibitory effects of these 3 CB2R agonists were abolished, suggesting that their effect is mediated through the CB2R. In WT, CB1R KO and CB2R KO mice, Non-selective CB receptor agonists WIN55, 212-2 also inhibited Ca2+ oscillations, 10 μmol/L of WIN55, 212-2 can reduced the 30 nmol/L ACh-induced Ca2+ oscillations current to (7.0±3.5)% (P=0.000, n=6), (5.0±6.9)% (P=0.000, n=6) and (5.0±9.3)% (P=0.000, n=6) respectively. but endogenous Non-selective cannabinoid substance, 2-AG did not show the inhibitory effect. Conclusion Cannabinoid ligands modulate mouse pancreatic acinar cell Ca2+ oscillations in a complex manner, through CB receptors or non-CB receptors. CB2R rather than CB1R plays a critical role in the regulation of Ca2+ signals in mouse pancreatic acinar cells. Key words: Cannabinoid receptor; Calcium signals; Pancreatic acinar cells; Patch clamp

All muscarinic acetylcholine receptors (M1-M5) are expressed in murine brain microvascular endothelium

Clinical and experimental studies indicate that muscarinic acetylcholine receptors are potential pharmacological targets for the treatment of neurological diseases. Although these receptors have been described in human, bovine and rat cerebral microvascular tissue, a subtype functional characterization in mouse brain endothelium is lacking. Here, we show that all muscarinic acetylcholine receptors (M1-M5) are expressed in mouse brain microvascular endothelial cells. The mRNA expression of M2, M3, and M5 correlates with their respective protein abundance, but a mismatch exists for M1 and M4 mRNA versus protein levels. Acetylcholine activates calcium transients in brain endothelium via muscarinic, but not nicotinic, receptors. Moreover, although M1 and M3 are the most abundant receptors, only a small fraction of M1 is present in the plasma membrane and functions in ACh-induced Ca2+ signaling. Bioinformatic analyses performed on eukaryotic muscarinic receptors demonstrate a high degree of conservation of the orthosteric binding site and a great variability of the allosteric site. In line with previous studies, this result indicates muscarinic acetylcholine receptors as potential pharmacological targets in future translational studies. We argue that research on drug development should especially focus on the allosteric binding sites of the M1 and M3 receptors.

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.

Enhanced transient receptor potential channel-mediated Ca2+ influx in the cells with phospholipase C-δ1 overexpression: its possible role in coronary artery spasm.

We reported that coronary spasm was induced in the transgenic mice with the increased phospholipase C (PLC)-δ1 activity. We investigated the effect of enhanced PLC-δ1 on Ca2+ influx and its underlying mechanisms. We used human embryonic kidney (HEK)-293 and coronary arteries smooth muscle cells (CASMC). Intracellular free Ca2+ concentration ([Ca2+ ]i ; nm) was measured by fura-2, and Ca2+ influx was evaluated by the increase in [Ca2+ ]i after addition of extracellular Ca2+ . Acetylcholine (ACh) was used to induce Ca2+ influx. ACh-induced peak Ca2+ influx was 19 ± 3 in control HEK-293 cells and 71 ± 8 in the cells with PLC-δ1 overexpression (P < 0.05 between two groups). Nifedipine partially suppressed this Ca2+ influx, whereas either 2-APB or knockdown of classical transient receptor potential channel 6 (TRPC6) blocked this Ca2+ influx. In the human CASMC, ACh-induced peak Ca2+ influx was 29 ± 6 in the control and was increased to 45 ± 16 by PLC-δ1 overexpression (P < 0.05). Like HEK-293 cells, pretreatment with nifedipine partially suppressed Ca2+ influx, whereas either 2-APB or knockdown of TRPC6 blocked it. ACh-induced Ca2+ influx was enhanced by PLC-δ1 overexpression, and was blocked partially by nifedipine and completely by 2-APB. TRPC-mediated Ca2+ influx may be related to the enhanced Ca2+ influx in PLC-δ1 overexpression.

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 Ca2+ signals may protect pancreatic acinar cells against Ca2+ 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 Ca2+ signals in pancreatic acinar cells is largely unknown. We evaluated the roles of CB2R agonist, GW405833 (GW) in agonist-induced Ca2+ 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 Ca2+ 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 Ca2+ oscillations, pancreatic amylase, and pulmonary myeloperoxidase. Collectively, we provide novel evidence that activation of CB2Rs eliminates ACh-induced Ca2+ oscillations and L-arginine-induced enhancement of Ca2+ signaling in mouse pancreatic acinar cells, which suggests a potential cellular mechanism of CB2R-mediated protection in acute pancreatitis.

Acetylcholine induces nitric oxide production by inducing intracellular Ca2+ oscillations in mouse brain endothelial cells

Basal forebrain neurons control intracortical arterioles by releasing acetylcholine (Ach), which stimulates endothelial cells (ECs) to produce the vasodilating gasotransmitter, nitric oxide (NO). Surprisingly, the mechanism by which Ach induces NO synthesis in brain ECs is still unknown. An increase in intracellular Ca2+ concentration ([Ca2+]i) recruits a multitude of endothelial Ca2+-dependent pathways, such as Ca2+/Calmodulin endothelial NO synthase (eNOS). The present investigation sought to investigate the role of intracellular Ca2+ signaling in Ach-induced NO production in bEnd5 cells, an established model of mouse brain microvascular ECs. Ach induced dose-dependent asynchronous Ca2+ oscillations in bEnd5 cells. Ach-evoked Ca2+ oscillations did not arise in the absence of external Ca2+ but rapidly resumed on Ca2+ restitution to the bath. However, nicotine, a selective agonist of the Ca2+-permeable nicotinic receptors, did not cause any detectable increase in [Ca2+]i. Pharmacological manipulation indeed revealed that Ach-induced Ca2+ spikes in bEnd5 cells are triggered by the interaction between intracellular Ca2+ release from InsP3 receptors (InsP3Rs) SOCE. Next, we found that Ach-induced NO production was hindered by L-NAME, a selective NOS inhibitor, and BAPTA, a membrane permeable intracellular Ca2+ buffer. Moreover, Ach-elicited NO synthesis was blocked by the pharmacological abrogation of the accompanying Ca2+ spikes. Ach stimulates bEnd5 cells by inducing a burst of intracellular Ca2+ spikes which is patterned by the interplay between ER-dependent Ca2+ mobilization and SOCE. Ach-elicited Ca2+ spikes result in NO production and are, therefore, predicted to control local CBF in mouse brain. Future experiments will assess whether this signaling pathway is altered in neurodegenerative disorders, such as Alzheimer’s Disease.

Small caliber arterial endothelial cells calcium signals elicited by PAR2 are preserved from endothelial dysfunction.

Endothelial cell (EC)-dependent vasodilation by proteinase-activated receptor 2 (PAR2) is preserved in small caliber arteries in disease states where vasodilation by muscarinic receptors is decreased. In this study, we identified and characterized the PAR2-mediated intracellular calcium (Ca2+)-release mechanisms in EC from small caliber arteries in healthy and diseased states. Mesenteric arterial EC were isolated from PAR2 wild-type (WT) and null mice, after saline (controls) or angiotensin II (AngII) infusion, for imaging intracellular calcium and characterizing the calcium-release system by immunofluorescence. EC Ca2+ signals comprised two forms of Ca2+-release events that had distinct spatial-temporal properties and occurred near either the plasmalemma (peripheral) or center of EC. In healthy EC, PAR2-dependent increases in the densities and firing rates of both forms of Ca2+-release were abolished by inositol 1,4,5- trisphosphate receptor (IP3R) inhibitor, but partially reduced by transient potential vanilloid channels inhibitor ruthenium red (RR). Acetylcholine (ACh)-induced less overall Ca2+-release than PAR2 activation, but enhanced selectively the incidence of central events. PAR2-dependent Ca2+-activity, inhibitors sensitivities, IP3R, small- and intermediate-conductance Ca2+-activated potassium channels expressions were unchanged in EC from AngII WT. However, the same cells exhibited decreases in ACh-induced Ca2+-release, RR sensitivity, and endothelial nitric oxide synthase expression, indicating AngII-induced dysfunction was differentiated by receptor, Ca2+-release, and downstream targets of EC activation. We conclude that PAR2 and muscarinic receptors selectively elicit two elementary Ca2+ signals in single EC. PAR2-selective IP3R-dependent peripheral Ca2+-release mechanisms are identical between healthy and diseased states. Further study of PAR2-selective Ca2+-release for eliciting pathological and/or normal EC functions is warranted.