Suppression of receptor-mediated Ca2+ mobilization and functional leukocyte responses by hyperforin

We have recently identified hyperforin, a lipophilic constituent of the herb Hypericum perforatum (St. John's wort), as a dual inhibitor of the proinflammatory enzymes cyclooxygenase-1 and 5-lipoxygenase. The aim of the present study was to further elucidate antiinflammatory properties and respective targets of hyperforin. We found that hyperforin inhibited the generation of reactive oxygen species (ROS) as well as the release of leukocyte elastase (degranulation) in human isolated polymorphonuclear leukocytes (PMNL), challenged by the G protein-coupled receptor (GPCR) ligand N-formyl-methionyl-leucyl-phenylalanine (fMLP) with an IC 50 approximately equal 0.3 microM. When PMNL were stimulated with phorbol-12-myristate-13-acetate (PMA) or ionomycin, hyperforin (up to 10 microM) failed to inhibit ROS production and elastase release, respectively. Moreover, hyperforin blocked receptor-mediated Ca(2+) mobilization ( IC 50 approximately equal 0.4 and 4 microM, respectively) in PMNL and monocytic cells, and caused a rapid decline of the intracellular Ca(2+) concentration in resting cells. In contrast, the Ca(2+) influx induced by ionomycin or thapsigargin was not suppressed. Comparative studies with the specific phospholipase C inhibitor U-73122 and hyperforin revealed similarities between both compounds. Thus, U-73122 and hyperforin blocked fMLP- and PAF-induced Ca(2+) mobilization, ROS formation, and elastase release, but failed to suppress these responses when cells were stimulated by PMA or ionomycin. Also, both compounds rapidly decreased basal Ca(2+) levels in resting cells and led to a rapid decline of the Ca(2+) elevations evoked by fMLP or PAF. Our data suggest that hyperforin targets component(s) within G protein signaling cascades that regulate Ca(2+) homeostasis, coupled to proinflammatory leukocyte functions.     

Involvement of p38 MAP kinase-mediated cytochrome c release on sphingosine-1-phosphate (S1P)- and N-monomethyl-S1P-induced cell death of PC12 cells

d-erythro-Sphingosine-1-phosphate (S1P), a sphingolipid metabolite, affects various neuronal functions including cell fate. S1P appears to have contradictory effects in PC12 cells, a neuronal model cell line; neurite retraction and cell survival/differentiation. In the present study, we examined whether S1P induces cell death in undifferentiated PC12 cells. Culture with S1P at 20 microM for 4 h caused lactate dehydrogenase leakage 24 h later. The response was reduced by an inhibitor of caspases and accompanied by the release of cytochrome c and DNA fragmentation. S1P caused the phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) within 10 min. An inhibitor of p38 MAPK (10 microM SB203580) inhibited both the release of cytochrome c and DNA fragmentation induced by S1P. Treatment with nerve growth factor or pertussis toxin (PTX) decreased S1P-induced phosphorylation of p38 MAPK and cell death. These findings suggest that S1P-activated p38 MAPK acts as a death signal upstream of the release of cytochrome c. N-Monomethyl-S1P (MM-S1P), a weak agonist in cells expressing S1P1 receptors, had marked effects (phosphorylation of p38 MAPK, release of cytochrome c and DNA fragmentation) at lower concentrations than S1P and in a PTX-sensitive manner. These findings show that the activation of S1P receptors by S1P and MM-S1P causes cell death accompanied by DNA fragmentation via the p38 MAPK pathway-mediated release of cytochrome c in PC12 cells. The potential of S1P and MM-S1P to act as agonists of S1P receptors and as intracellular messengers is discussed.     

Synergistic effects of hydrogen peroxide and ethanol on cell viability loss in PC12 cells by increase in mitochondrial permeability transition

The promoting effect of ethanol against the cytotoxicity of hydrogen peroxide (H2O2) in differentiated PC12 cells was assessed by measuring the effect on the mitochondrial membrane permeability. Treatment of PC12 cells with H2O2 resulted in the nuclear damage, decrease in the mitochondrial transmembrane potential, cytosolic accumulation of cytochrome c, activation of caspase-3, increase in the formation of reactive oxygen species (ROS) and depletion of GSH. In PC12 cells and dopaminergic neuroblastoma SH-SY5Y cells, the promoting effect of ethanol on the H2O2-induced cell death was increased with exposure time. Ethanol promoted the nuclear damage, change in the mitochondrial membrane permeability, ROS formation and decrease in GSH contents due to H2O2 in PC12 cells. Catalase, carboxy-PTIO, Mn-TBAP, N-acetylcysteine, cyclosporin A and trifluoperazine inhibited the H2O2 and ethanol-induced mitochondrial dysfunction and cell injury. The results show that the ethanol treatment promotes the cytotoxicity of H2O2 against PC12 cells. Ethanol may enhance the H2O2-induced viability loss in PC12 cells by promoting the mitochondrial membrane permeability change, release of cytochrome c and subsequent activation of caspase-3, which is associated with the increased formation of ROS and depletion of GSH. The findings suggest that ethanol as a promoting agent for the formation of mitochondrial permeability transition may enhance the neuronal cell injury caused by oxidants.     

Neuroprotective effect of some plant extracts in cultured CT105-induced PC12 cells

Carboxyl-terminal fragments of APP (CT) have been found in plaques, microvessels and the neurofibrillary tangles in the brains of AD patients. These carboxyl-terminal fragments, which contain the complete Abeta sequence, appear to be toxic to neurons in culture cells. However, the possible role of other cleaved products of APP is less clear. We showed that a recombinant carboxy-terminal 105 amino acid fragment (CT105) of APP induced strong neurotoxicity in PC12 cells. We prepared alcoholic extract from Oriental herbal plants and screened their protective effects against CT105-induced cell death in PC12 cells after the treatment of these extracts. Of the 10 kinds of plant extracts, 12 kinds of extracts had considerable protective effects against CT105-induced cell death, especially, Uncariae Ramulus et Uncus (UREU), Gastrodia elata (GAE), Evodia officinalis (EO) and Panax ginseng (PAG) showed the most protective effect at the concentration of 50 microg/ml. BuOH extract of UREU and GAE possessed the strongest protective effects against neurotoxicity of CT105-induced PC12 cells and showed inhibitory effect with IC50 values of 4.8 and 8.3 microg/ml, respectively. These plants are promising candidates of neuroprotective effects and would be useful for the treatment of the neuronal degenerative diseases such as Alzheimer's diseases.     

Aggravation of L-DOPA-induced neurotoxicity by tetrahydropapaveroline in PC12 cells

Tetrahydropapaveroline (THP) is formed in Parkinsonian patients receiving L-DOPA therapy and is detected in the plasma and urine of these patients. In this study, we have investigated the effects of THP on L-DOPA-induced neurotoxicity in cultured rat adrenal pheochromocytoma, PC12 cells. Exposure of PC12 cells up to 10 microM THP or 20 microM L-DOPA after 24 or 48 hr, neither affected the cell viability determined by MTT assay, nor induced apoptosis by flow cytometry and TUNEL staining. However, at concentrations higher than 15 microM, THP showed cytotoxicity through an apoptotic process. In addition, THP at 5-15 microM for both incubation time points significantly enhanced L-DOPA-induced neurotoxicity (L-DOPA concentration, 50 microM). Exposure of PC12 cells to THP, L-DOPA and THP plus L-DOPA for 48 hr resulted in a marked increase in the cell loss and percentage of apoptotic cells compared with exposure for 24hr. The enhancing effects of THP on L-DOPA-induced neurotoxicity were concentration- and treated-time-dependent. THP, L-DOPA and THP plus L-DOPA produced a significant increase in intracellular reactive oxygen species generation and decrease in ATP levels, supporting the involvement of oxidative stress in THP- and L-DOPA-induced apoptosis. The antioxidant N-acetyl-L-cysteine strongly inhibited changes in apoptosis, decreases in cell viability and ROS generation induced by THP associated with L-DOPA. These results suggest that THP aggravates L-DOPA-induced oxidative neurotoxic and apoptotic effects in PC12 cells. Therefore, Parkinsonian patients treated with L-DOPA for long-term need to be monitored for the relationship between plasma concentration of THP and the symptoms of neurotoxicity.     

Effects of carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone on the growth inhibition in human pulmonary adenocarcinoma Calu-6 cells

Carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) is an uncoupler of mitochondrial oxidative phosphorylation in eukaryotic cells. Here, we evaluated the in vitro effects of FCCP on the growth of Calu-6 lung cancer cells. FCCP inhibited the growth of Calu-6 cells with an IC₅₀ of approximately 6.64 ± 1.84 μM at 72 h, as shown by MTT. DNA flow cytometric analysis indicated that FCCP induced G1 phase arrest below 20 μM of FCCP. Treatment with FCCP decreased the level of CDKs and cyclines in relation to G1 phase. In addition, FCCP not only increased the p27 level but also enhanced its binding with CDK4, which was associated with hypophosphorylation of Rb protein. While transfection of p27 siRNA inhibited G1 phase arrest in FCCP-treated cells, it did not enhance Rb phosphorylation. FCCP also efficiently induced apoptosis. The apoptotic process was accompanied with an increase in sub-G1 cells, annexin V staining cells, mitochondria membrane potential (MMP) loss and cleavage of PARP protein. All of the caspase inhibitors (caspase-3, -8, -9 and pan-caspase inhibitor) markedly rescued the Calu-6 cells from FCCP-induced cell death. However, knock down of p27 protein intensified FCCP-induced cell death. Moreover, FCCP induced the depletion of GSH content in Calu-6 cells, which was prevented by all of the caspase inhibitors. In summary, our results demonstrated that FCCP inhibits the growth of Calu-6 cells in vitro. The growth inhibitory effect of FCCP might be mediated by cell cycle arrest and apoptosis via decrease of CDKs and caspase activation, respectively. These findings now provide a better elucidation of the mechanisms involved in FCCP-induced growth inhibition in lung cancer.     

Low pH enhances 2-aminoethoxydiphenyl borate-induced cell death of PC12 cells

2-Aminoethoxydiphenyl borate (2-APB) is widely used as a pharmacological tool for analysis of cellular Ca²⁺ regulation. In this study, we found that external acid potentiated neural cell death induced by 2-APB in rat pheochromocytoma 12 (PC12) cells. 2-APB induced cell death in half of the PC12 cells within 30 min at pH 6.6 but not at pH 7.4. The extent of the 2-APB-induced cell death increased in a dose-, time- and pH-dependent manner. Ca²⁺-imaging revealed that 2-APB increased [Ca²⁺]_i in PC12 cells at pH 6.6. Removal of extracellular Ca²⁺ and chelation of intracellular Ca²⁺ inhibited the 2-APB-induced cell death. Antagonists of the store-operated Ca²⁺ (SOC) channel (SKF96365 and ruthenium red) blocked both 2-APB-induced cell death and Ca²⁺ influx, but those for transient receptor potential channels (BCTC, TRIM and BTP2), acid-sensing ion channels (amiloride) and proton-sensing G-protein-coupled receptors (U73122) did not. These results suggest that 2-APB induces neural cell death via Ca²⁺ overload through SOC channel activation under acidic pH.     

三羟基异黄酮对APP695基因转染PC12细胞凋亡的保护作用

目的探讨植物雌激素三羟基异黄酮(Genistein,GST)对APP695基因转染PC12细胞凋亡的保护作用及机制。方法用pIRES2-EGFP空载体和pIRES2-EGFP/APP695MT表达载体转染正常的PC12细胞,将细胞分为对照组、空载组、APP695转染组、GST干预组。应用流式细胞仪测定细胞凋亡率,免疫细胞化学SABC法和Western blot方法检测凋亡相关蛋白Caspase-3的表达。结果 APP695转染组与空载组比较,PC12细胞凋亡率明显升高(P<0.01),Caspase-3为强阳性表达(P<0.01);GST干预组与APP695转染组比较,PC12细胞凋亡率明显降低(P<0.01),Caspase-3的免疫反应产物明显减弱(P<0.01),且15μmol.L-1和20μmol.L-1 GST处理组与5μmol.L-1和10μmol.L-1 GST处理组比较,Caspase-3的免疫反应产物减弱更明显(P<0.01)。结论 GST能降低APP695基因转染的PC12细胞凋亡率,其机制可能与减少凋亡蛋白Caspase-3的表达有关。     

Caged agonist of P2Y1 and P2Y12 receptors for light-directed facilitation of platelet aggregation

We have prepared a caged form (MRS2703) of a potent dual agonist of the P2Y(1) and P2Y(12) nucleotide receptors, 2-MeSADP, by blocking the beta-phosphate group with a 1-(3,4-dimethyloxyphenyl)eth-1-yl phosphoester. Although MRS2703 is itself inactive at human P2Y(1) and P2Y(12) receptors expressed heterologously in 1321N1 astrocytoma cells or in washed human platelets, this derivative readily regenerates the parent agonist upon mild irradiation with long-wave UV light (360 nm). The functional effect of the regenerated agonist was demonstrated by a rise in intracellular calcium mediated by either P2Y(1) or P2Y(12) receptors in transfected cells. Washed human platelets exposed to a solution of MRS2703 were induced to aggregate upon UV irradiation. At 1.0 microM MRS2703, full aggregation was achieved within 1 min of irradiation. Thus, this caged nucleotide promises to be a useful probe for potent P2Y receptor activation with light-directed spatial and temporal control.     

Hyperforin activates nonselective cation channels (NSCCs)

A large body of evidence supports the preclinical antidepressant profile of hyperforin including inhibition of the synaptosomal uptake of several neurotransmitters by hyperforin and studies in behavioural models. In contrast to other antidepressants, hyperforin does not directly inhibit neurotransmitter transporters, but instead uptake inhibition seems to be the consequence of an elevated intracellular sodium concentration ([Na+]i). The mechanism of hyperforin-induced elevation of [Na+]i was investigated using two different cell types: human platelets and rat pheochromocytoma cells (PC12 cells). In both cell systems, hyperforin increased both [Na+]i and free intracellular Ca2+ concentration ([Ca2+]i). One pathway for Na+ and Ca2+ entry is mediated by nonselective cation channels (NSCCs), which can be blocked by SK&F 96365 and LOE 908. LOE 908 is a blocker of both NSCC1 and NSCC2 subclasses, while SK&F 96365 blocks NSCC2 only. Both SK&F 96365 and LOE 908 completely inhibited the hyperforin-induced influx of Na+ and Ca2+ into platelets and PC12 cells. This indicates that hyperforin is mainly active upon NSCC2. The effect of hyperforin is inhibited by La3+ and Gd3+, indicating that there is a potential homology with canonical transient receptor potential protein channels (TRPC channels). Moreover, La3+ and Gd3+ attenuate the effect of hyperforin on serotonin uptake in human platelets. Additionally, hyperforin induces barium influx in PC12 cells and this influx can be inhibited by SK&F 96365, LOE 908, Gd3+ and La3+. In summary, these findings suggest that hyperforin represents a new principle for preclinical antidepressant activity, modulating brain neurotransmission by inhibition of neurotransmitter uptake via activation of NSCCs.British Journal of Pharmacology (2005) 145, 75-83. doi:10.1038/sj.bjp.0706155.     

Cellular transformation of the investigational new anticancer drug NB1011, a phosphoramidate of 5-(2-bromovinyl)-2'-deoxyuridine,results in modification of cellular proteins not DNA

NB1011 [E-5-(2-bromovinyl)-2'-deoxyuridine-5'-(L-methylalaninyl)-phenylphosphoramidate], a phosphoramidate prodrug of E-5-(2-bromovinyl)-2'-deoxyuridine-5'-monophosphate (BVdUMP), is an investigational new anticancer drug. NB1011 targets thymidylate synthase (TS), which catalyzes the transformation of BVdUMP into cytotoxic reaction products. Due to the elevated levels of TS expression in tumor cells compared to normal cells, these cytotoxic products are preferentially generated inside tumor cells, and, as expected, NB1011 is more toxic to cells with higher levels of TS expression. Therefore, NB1011 therapy should kill tumor cells without severely damaging normal cells. Radiolabeled NB1011 was used to determine the intracellular fate of NB1011 reaction products and, possibly, the mechanism of action of this investigational new drug. We found significant incorporation of the radiolabel into cellular macromolecules. In contrast to our expectations that NB1011 product(s) would be incorporated into DNA, we discovered that cellular proteins were the labeled macromolecular fraction. Herein, we report that the intracellular transformation of NB1011 involves formation of the corresponding monophosphate, TS-dependent transformation into highly reactive intermediates, and subsequent incorporation into cellular proteins. TS itself appears to escape irreversible inactivation. Our data suggest that protein modification not DNA incorporation accounts for the therapeutic effect of NB1011. The proposed mechanism is rather unexpected for a nucleotide analogue and could lead to the discovery of new cellular protein targets for future drug design.     

In vitro effects of the dicyclohexylammonium salt of hyperforin on interleukin-6 release in different experimental models

Cytokine hypersecretion might be involved in the onset and maintenance of depressive disorders and it has been suggested that St. John's wort extracts (Hypericum perforatum, SJW) might exert their antidepressant-like effects by affecting peripheral interleukin-6 (IL6) expression. We found that hyperforin, one putative active principle of SJW, and its dicyclohexylammonium salt (hyperforin-DCHA), inhibited the substance P (SP)-induced [L6 release inhuman astrocytoma cells (U373MG) with an Cs50 of 1.6 pM, indicating that hyperforin is likely to account for the inhibitory effect previously found in the same experimental model with SJW ex-tracts. [3H]SP binding experiments in parallel on the same intact cells indicate that hyperforin-DCHA does not interact with neuro-kinin-I receptors but very likely interacts with some intracellular steps leading to the synthesis and/or release of IL6. Hyperforin-DCHA also inhibited, with a similar IC50, the IL6 release induced in U373MG cells by two other classic proinflammatory stimuli,ILl and lipopolysaccharide (LPS), as well as the LPS-induced IL6 release in whole rat blood. Hyperforin-DCHA was less active in whole human blood. The concentrations required in vitro to inhibit LPS-induced IL6 release from rat and human whole blood are about one order of magnitude higher than the hyperforin levels measured in the plasma of rats or humans treated with pharmaco-logically active doses of SJW or hyperforin-DCHA.     

Inhibition of calcium uptake and catecholamine release by 8-(n,n-diethylamino)- octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) In cultured bovine adrenal chromaffin cells

Effects of intracellular calcium antagonists, 8-(f,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) and 1-(5-(p-nitrophenyl)-furfurylidene-amino) hydantoin sodium hydrate (dantrolene sodium), on catecholamine release and ⁴⁵Ca²⁺ uptake were studied using cultured bovine adrenal chromaffin cells. TMB-8 inhibited carbamylcholine-evoked catecholamine release and ⁴⁵Ca²⁺ uptake in a concentration-dependent manner with a similar potency. On the contrary, dantrolene sodium did not show obvious inhibitory effects of catecholamine release and ⁴⁵Ca²⁺ uptake. Although TMB-8 inhibited the high K⁺-evoked catecholamine release and ⁴⁵Ca²⁺ uptake, the potency of the drug was approximately 100-fold less than when used to inhibit the carbamylcholine-evoked catecholamine release and ⁴⁵Ca²⁺ uptake. The inhibitory effect of TMB-8 on the carbamylcholine-evoked catecholamine release was not overcome by an increase in an extracellular calcium concentration, and was not due to competitive antagonism at the nicotinic receptor site. Moreover, TMB-8 inhibited the carbamylcholine-stimulated ⁴⁵Ca²⁺ efflux, but dantrolene sodium failed to affect it. These results suggest that TMB-8, a well-known intracellular calcium antagonist, prevents the cellular calcium uptake in cultured adrenal chromaffin cells, and thus prevents catecholamine release.     

Effects of synthetic sphingosine-1-phosphate analogs on arachidonic acid metabolism and cell death

Sphingolipid metabolites such as sphingosine regulate cell functions including cell death and arachidonic acid (AA) metabolism. D-erythro-C18-Sphingosine-1-phosphate (D-e-S1P), a sphingolipid metabolite, acts as an intracellular messenger in addition to being an endogenous ligand of some cell surface receptors. The development of S1P analogs may be useful for studying and/or regulating S1P-mediated cellular responses. In the present study, we found that several synthetic S1P analogs at pharmacological concentrations stimulated AA metabolism and cell death in PC12 cells. D-erythro-N,O,O-Trimethyl-C18-S1P (D-e-TM-S1P), L-threo-O,O-dimethyl-C18-S1P (L-t-DM-S1P) and L-threo-O,O-dimethyl-3O-benzyl-C18-S1P (L-t-DMBn-S1P) at 100 microM stimulated [(3)H]AA release from the prelabeled PC12 cells. L-t-DMBn-S1P at 20 microM increased prostanoid formation in PC12 cells. L-t-DMBn-S1P-induced AA release was inhibited by D-e-sphingosine, but not by the tested PLA(2) inhibitors. L-t-DMBn-S1P did not stimulate the activity of cytosolic phospholipase A(2alpha) (cPLA(2alpha)) in vitro and the translocation of cPLA(2alpha) in the cells, and caused AA release from the cells lacking cPLA(2alpha). These findings suggest that L-t-DMBn-S1P stimulated AA release in a cPLA(2alpha)-independent manner. In contrast, D-e-S1P and D-erythro-N-monomethyl-C18-S1P caused cell death without AA release in PC12 cells, and the effects of D-e-TM-S1P, L-t-DM-S1P and L-t-DMBn-S1P on cell death were limited. Synthetic S1P analogs may be useful tools for studying AA metabolism and cell death in cells.     

Cholesteryl-hemisuccinate-induced apoptosis of promyelocytic leukemia HL-60 cells through a cyclosporin A-insensitive mechanism

We reported previously that alpha-tocopheryl-succinate (VES) induced apoptosis of cultured human promyelocytic leukemia cells (HL-60) (Free Radic Res 2000;33:407-18). We have now studied the effect of cholesteryl-hemisuccinate (CS) on the fate of HL-60 cells to clarify whether CS has an effect similar to that of VES. CS inhibited the growth of HL-60 cells without differentiation to granulocytes and induced DNA fragmentation and ladder formation. CS inhibited the phosphorylation of pleckstrin homology domain-containing protein kinase B (Akt) and initiated the activation of a caspase cascade. CS triggered the reaction leading to the cleavage of Bid and also released cytochrome c (Cyt. c) from mitochondria. In addition, CS induced mitochondrial membrane depolarization and translocation of Bax to mitochondria in HL-60 cells. However, CS did not induce an increase in the concentration of intracellular calcium ions in HL-60 cells. The membrane depolarization, Cyt. c release, and DNA fragmentation were inhibited by z-VAD-fluoromethylketone (z-VAD-fmk), a pan-caspase inhibitor, but not by cyclosporin A, an inhibitor of membrane permeability transition. These results suggested that CS-induced apoptosis of HL-60 cells might be caused by inhibiting Akt phosphorylation following cleavage of Bid through caspase-8 activation and subsequently via an Apaf complex-caspase cascade pathway.     

Protection by ascorbic acid from denaturation and release of cytochrome c, alteration of mitochondrial membrane potential and activation of multiple caspases induced by H(2)O(2), in human leukemia cells

We investigated peroxide and superoxide accumulation, cytochrome c nature and release from mitochondria, as well as caspase activation during exposure of HL-60 cells to H(2)O(2) and the protective effect of ascorbic acid. Exposure of the cells to 100 microM H(2)O(2) resulted in intracellular accumulation of peroxides, denaturation of cytochrome c that was identified in the mitochondria and cytosol, release of native cytochrome c to the cytosol and fall in mitochondrial membrane potential (DeltaPsi(m)). Loading of cells with ascorbic acid before exposure to H(2)O(2) resulted in a dose-dependent protective effect against: intracellular accumulation of peroxides, DeltaPsi(m) alteration, cytochrome c denaturation and release. The accumulation of peroxides induced processings and activations of procaspase-8, -9 and -3. Double staining with antiserum which recognizes the p18 subunit of cleaved caspase-3 and with Hoechst had shown that a high percentage of cells exposed to 100 microM H(2)O(2) stained positively with the antibody and showed features of apoptosis. Ascorbic acid loading prevented caspase activation induced by H(2)O(2). We conclude that ascorbic acid protects against activation of apoptotic cascades in HL-60 cells exposed to H(2)O(2) and against apoptosis.     

Inhibitory effects of (1R,9S)-β-hydrastine on calcium transport in PC12 cells

(1R,9S)-beta-Hydrastine (BHS), at 100 microM, has been shown to mainly reduce the K+-induced dopamine release and Ca2+ influx by blocking the L-type Ca2+ channel and inhibit the caffeine activated store-operated Ca2+ channels, but not those activated by thapsigargin, in PC12 cells. In this study, the effects of BHS on Ca2+ transport from Ca2+ stores in the absence of external Ca2+ were investigated in PC12 cells. BHS decreased the basal intracellular Ca2+ concentration ([Ca2+]i) in the absence of external Ca2+ in PC12 cells. In the absence of external Ca2+, pretreating PC12 cells with 100 microM BHS reduced the rapid increase in the [Ca2+]i elicited by 20 mM caffeine, but not that by 1 microM thapsigargin. In addition, BHS inhibited the increase in the [Ca2+]i elicited by restoration of 2 mM CaCl2 after the Ca2+ stores had been depleted by 20 mM caffeine, but not those depleted by 1 microM thapsigargin, in the absence of external Ca2+. These results suggested that BHS mainly inhibited Ca2+ leakage from the Ca2+ stores and the caffeine-stimulated release of Ca2+ from the caffeine-sensitive Ca2+ stores in PC12 cells.