thapsigargin and Carcinoma--Squamous-Cell

Treatment with analogues of the SERCA-inhibitor Thapsigargin is a promising new approach for a wide variety of cancer entities. However, our previous studies on various tumor cells suggested resistance of SEC62 over-expressing tumors to this treatment. Therefore, we proposed the novel concept that e.g. lung-, prostate-, and thyroid-cancer patients should be tested for SEC62 over-expression, and developed a novel therapeutic strategy for a combinatorial treatment of SEC62 over-expressing tumors. The latter was based on the observations that treatment of SEC62 over-expressing tumor cells with SEC62-targeting siRNAs showed less resistance to Thapsigargin as well as a reduction in migratory potential and that the siRNA effects can be mimicked by the Calmodulin antagonist Trifluoperazine. Therefore, the combinatorial treatment of SEC62 over-expressing tumors was proposed to involve Thapsigargin and Trifluoperazine. Here, we addressed the impact of Thapsigargin and Trifluoperazine in separate and combined treatments of heterotopic tumors, induced by inoculation of human hypopharyngeal squamous cell carcinoma (FaDu)-cells into the mouse flank. Seeding of the tumor cells and/or their growth rate were significantly reduced by all three treatments, suggesting Trifluoperazine is a small molecule to be considered for future therapeutic strategies for patients, suffering from Sec62-overproducing tumors.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Calmodulin; Carcinoma, Squamous Cell; Cell Line, Tumor; Cell Proliferation; Enzyme Inhibitors; Head and Neck Neoplasms; Humans; Hypopharyngeal Neoplasms; Membrane Transport Proteins; Mice; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Squamous Cell Carcinoma of Head and Neck; Thapsigargin; Trifluoperazine

Calcium signal plays an important role in a variety of cancer cell metabolism, but knowledge on its role in head and neck squamous cell carcinoma (HNSCC) is limited. Store-operated calcium entry (SOCE) is the principal Ca2+ entry mechanism that maintains calcium concentration and produces calcium signal in non-excitable cells. SOCE is triggered by stromal interaction molecule 1 (STIM1), which is located in endoplasmic reticulum (ER) as Ca2+ sensor. Although, many studies demonstrated that STIM1 and SOCE play important functions in the regulation of many cancer progressions, their clinical relevance in HNSCC remains unclear. In this study, STIM1 expression levels notably increased in 89% HNSCC tissues compared with those in adjacent normal tissues. Meanwhile, this overexpression was close associated with tumor size but not with neck lymph node metastasis. Thus, this study mainly focuses on STIM1 function in HNSCC tumor growth. Three HNSCC cell lines, namely, TSCCA (oral cancer cell line) and Hep2 (laryngeal cell line) with high STIM1 expression levels and Tb3.1 (oral cancer cell line) with STIM1 expression level lower than previous two cell lines, were selected for in vitro study. Downregulated STIM1 expression levels in TSCCA and Hep2 arrested cells in G0/G1 stages, promoted cell apoptosis, and inhibited cell proliferation. By contrast, upregulated STIM1 expression in Tb3.1 inhibited cell apoptosis and promoted cell proliferation. Induced by thapsigargin (TG), ER stress was amplified when STIM1 expression was downregulated but was attenuated as STIM1 expression was upregulated. Furthermore, TSCCA cell xenograft models confirmed that STIM1 could promote HNSCC tumor growth in vivo. The present study provides new insight into HNSCC molecular mechanism and potential therapeutic target through targeting SOCE-dependent process. However, whether STIM1 participates in HNSCC metastasis requires further study.

Topics: Animals; Antineoplastic Agents; Apoptosis; Blotting, Western; Carcinoma, Squamous Cell; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Endoplasmic Reticulum Stress; Gene Expression Regulation, Neoplastic; Head and Neck Neoplasms; Humans; Mice; Mice, Nude; Real-Time Polymerase Chain Reaction; Squamous Cell Carcinoma of Head and Neck; Stromal Interaction Molecule 1; Thapsigargin; Xenograft Model Antitumor Assays

Cancer stem cells (CSCs) drive tumour spread and therapeutic resistance, and can undergo epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET) to switch between epithelial and post-EMT sub-populations. Examining oral squamous cell carcinoma (OSCC), we now show that increased phenotypic plasticity, the ability to undergo EMT/MET, underlies increased CSC therapeutic resistance within both the epithelial and post-EMT sub-populations. The post-EMT CSCs that possess plasticity exhibit particularly enhanced therapeutic resistance and are defined by a CD44(high)EpCAM(low/-) CD24(+) cell surface marker profile. Treatment with TGFβ and retinoic acid (RA) enabled enrichment of this sub-population for therapeutic testing, through which the endoplasmic reticulum (ER) stressor and autophagy inhibitor Thapsigargin was shown to selectively target these cells. Demonstration of the link between phenotypic plasticity and therapeutic resistance, and development of an in vitro method for enrichment of a highly resistant CSC sub-population, provides an opportunity for the development of improved chemotherapeutic agents that can eliminate CSCs.

Topics: Animals; Antineoplastic Agents; Carcinoma, Squamous Cell; CD24 Antigen; Cell Line; Cell Line, Tumor; Drug Resistance, Neoplasm; Epithelial Cell Adhesion Molecule; Epithelial-Mesenchymal Transition; Female; Humans; Hyaluronan Receptors; Male; Mice; Mice, Inbred NOD; Mice, SCID; Mouth Neoplasms; Neoplastic Stem Cells; Phenotype; Thapsigargin; Transforming Growth Factor beta; Tretinoin

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent for esophageal squamous cell carcinoma (ESCC). Forced expression of CHOP, one of the key downstream transcription factors during endoplasmic reticulum (ER) stress, upregulates the death receptor 5 (DR5) levels and promotes oxidative stress and cell death. In this study, we show that ER stress mediated by thapsigargin promoted CHOP and DR5 synthesis thus sensitizing TRAIL treatment, which induced ESCC cells apoptosis. These effects were reversed by DR5 siRNA in vitro and CHOP siRNA both in vitro and in vivo. Besides, chemically inhibition of AMPK by Compound C and AMPK siRNA weakened the anti-cancer effect of thapsigargin and TRAIL co-treatment. Therefore, our findings suggest ER stress effectively sensitizes human ESCC to TRAIL-mediated apoptosis via the TRAIL-DR5-AMPK signaling pathway, and that activation of ER stress may be beneficial for improving the efficacy of TRAIL-based anti-cancer therapy.

Topics: AMP-Activated Protein Kinases; Antineoplastic Agents; Apoptosis; Carcinoma, Squamous Cell; Cell Adhesion; Cell Line, Tumor; Cell Movement; Cell Survival; Drug Synergism; Drug Therapy, Combination; Endoplasmic Reticulum Stress; Enzyme Activation; Esophageal Neoplasms; Esophageal Squamous Cell Carcinoma; Humans; Neoplasm Invasiveness; Reactive Oxygen Species; Receptors, TNF-Related Apoptosis-Inducing Ligand; RNA, Small Interfering; Thapsigargin; TNF-Related Apoptosis-Inducing Ligand; Transcription Factor CHOP; Up-Regulation

To explore the apoptotic effect of ubiquitin-proteasome inhibitor (PI) MG-132 on human tongue squamous cell carcinoma cell line (Tca-8113 cell) through endoplasmic reticulum stress.. Tca-8113 cells were cultured in RPMI 1640 medium supplemented with 10% fetal calf serum, the exponential cells were divided into 5 groups.The cell culture medium was added to 1640 (negative control group), thapsigargin 5 μmol/L (positive control group), and 10,20,30 μmol/L (MG-132 group). After 24 h, the following experiments were carried out: morphological change of apoptotic cells was observed by Hoechst 33258 fluorescent staining under fluorescent microscope, apoptotic rate of cells was determined with annexin V-FITC/PI double staining by flow cytometry, the GRP78 mRNA level was determined by RT-PCR, the expression of caspase-12 protein was evaluated by Western blot, the human ubiquitin-protein ligase E3 concentration was detected by ELISA. The data was analyzed using SPSS16.0 software package.. Typical morphological change of apoptosis in Tca-8113 cells was observed 24 hours after treating with 10.0, 20.0, 30.0 μmol/L MG-132 and positive control group; The apoptotic rate of MG-132 groups gradually increased with MG-132 concentration; The GRP78 mRNA level was up-regulated; The expression of caspase-12 increased was demonstrated by Western blot; The expression of the human ubiquitin-protein ligase E3 in MG-132 groups was 28.75 ± 2.28, 18.16 ± 0.65 and 8.85 ± 0.72.. MG-132 can induce apoptosis of Tca-8113 cells through endoplasmic reticulum stress; MG-132 can inhibit the expression of human ubiquitin ligase E3.

Topics: Animals; Apoptosis; Carcinoma, Squamous Cell; Cell Line; Endoplasmic Reticulum Chaperone BiP; Heat-Shock Proteins; Humans; Leupeptins; Thapsigargin; Tongue Neoplasms

The aim of this study was to investigate the apoptotic effect of a proteasome inhibitor MG-132 on Tca-8113, a cell line of human tongue squamous cell carcinoma. Tca-8113 cells were treated with 10, 20, and 30μM of MG-132, or 5μM thapsigargin. Apoptosis rate was determined with annexin V/propidium iodide double staining. Expression of E3ubiquitin-protein ligase was determined by ELISA, and Grp78 and caspase-12 mRNA, and Grp78 and caspase-12 protein was assessed by RT-PCR and Western blot, respectively. Apoptosis was observed 18h after MG-132 treatment. The apoptotic rate in the 10, 20, and 30μM MG-132 group was 13.5, 19.6 and 34.7%, respectively, which was higher than in the thapsigargin (8.5%, P<0.01) or control group (0.5%, P<0.01). The expression of E3 ubiquitin-protein ligase in the 10, 20, and 30μM MG-132 group was 28.75±2.28, 18.16±0.65, 8.85±0.72, respectively, which was lower than in the thapsigargin (38.96±0.33, P<0.05 or 0.01) or control (40.88±4.52, P<0.05 or 0.01) group. The levels of Grp78 and capase-12 mRNA, Grp78 and caspase-12 protein in the MG-132 groups were higher than in the control group (P<0.01). In conclusion, MG-132 induces apoptosis in Tca-8113 cells in a concentration-dependent manner. The MG-132-induced apoptosis may involve downregulation of E3 ubiquitin ligase, and upregulation of Grp78 and caspase-12.

Topics: Antineoplastic Agents; Apoptosis; Carcinoma, Squamous Cell; Caspase 12; Cell Line, Tumor; Cysteine Proteinase Inhibitors; Endoplasmic Reticulum Chaperone BiP; Heat-Shock Proteins; Humans; Leupeptins; RNA, Messenger; Thapsigargin; Tongue Neoplasms; Ubiquitin-Protein Ligases

Our investigation aims to evaluate the significance of TRB3, an endoplasmic reticulum stress (ERS)-inducible gene, and explore its relationship with AKT in oral tongue squamous cell carcinoma (OTSCC). Expression of TRB3 and phosphorylated AKT (p-AKT) in OTSCC tissues and adjacent normal tissues were assessed by RT-PCR, Western blot and immunohistochemistry assay. Correlation of TRB3 and AKT was validated by TRB3 adenovirus plasmid (Ad-TRB3) transfection and short hairpin RNA (shRNA) inhibition. The mRNA expression of TRB3 was significantly higher than adjacent noncancerous tissues by RT-PCR in 15 of 18 specimens of OTSCC (83.3%, P<0.01). Both of TRB3 and AKT were highly expressed in 13 of 18 (72.2%) specimens of OTSCC comparing with adjacent noncancerous tissues by Western blot assay (P<0.05). TRB3 was significantly elevated in 49.2% (63/128) of pathologically confirmed specimens and 13.3% (4/30) of adjacent noncancerous specimens by immunohistochemical analysis (P<0.01). TRB3 overexpression was closely correlated with tumor pathological T stage, lymph node metastasis and tumor recurrence. In addition, both mRNA and protein expression of TRB3 was increased under thapsigargin (TG) or tunicmycin (TU)-induced ERS in Tca8113 and CAL-27 cells. Moreover, expression of p-AKT protein decreased when Ad-TRB3 was transected with OTSCC Tca8113 cells. However, expression of p-AKT protein increased when TRB3 was inhibited by TRB3 shRNA inhibition. TRB3 expression was closely correlated with OTSCC prognosis. Under ERS, TRB3 was up-regulated, resulting in inhibiting the activation of AKT in OTSCC.

Topics: Antiviral Agents; Biomarkers, Tumor; Blotting, Western; Carcinoma, Squamous Cell; Cell Cycle Proteins; Endoplasmic Reticulum Stress; Enzyme Inhibitors; Female; Humans; Lymphatic Metastasis; Male; Middle Aged; Neoplasm Recurrence, Local; Phosphorylation; Prognosis; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Repressor Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA, Small Interfering; Thapsigargin; Tongue Neoplasms; Tunicamycin

The histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), enhances cisplatin [cis-diammine dichloroplatinum (II)] (CDDP)-induced apoptosis in the oral squamous cell carcinoma (OSCC) cell line by complex, multifunctional mechanisms. We investigated the role of endoplasmic reticulum (ER) stress in the enhancing effect of SAHA on CDDP, compared with the ER stressor thapsigargin.. We chose OSCC cell line HSC-3 to ascertain the mechanism of SAHA-enhanced cytotoxicity among various cell lines. HSC-3 cells were incubated with CDDP/SAHA for 48 h, followed by the assessment of cell chemosensitivity to CDDP with MTT and TUNEL assays. Western blot analysis was used to detect the expressions of ER-related molecules, and flow cytometry was used to monitor caspase activity.. Treatment with CDDP/SAHA potently induced apoptosis in HSC-3 cells with a significant increase in caspase-4 and -12 functions. For example, 60% of cells became apoptotic after 48 h of treatment with CDDP/SAHA. In addition, SAHA alone rapidly induced sustained phosphorylation of eukaryotic translation initiation factor-2 (eIF2)alpha, which is up-regulated during ER stress. Inhibition of ER stress by salubrinal, an inhibitor of eIF2alpha dephosphorylation, abrogated SAHA's enhancement of CDDP cytotoxicity. Levels of phospho-Akt are decreased in SAHA-treated cells, and this is in turn associated with increased activity of protein phosphatase 1 (PP1) by SAHA, the phosphatase upstream of Akt.. These data indicate that up-regulation of specific-ER stress-associated events is an integral part of the mechanism by which SAHA enhances CDDP-induced apoptosis, and PP1 up-regulation followed by Akt dephosphorylation plays an important role in SAHA-enhanced CDDP apoptosis.

Topics: Apoptosis; Carcinoma, Squamous Cell; Caspase 12; Caspase Inhibitors; Caspases, Initiator; Cell Line, Tumor; Cinnamates; Cisplatin; Drug Synergism; Endoplasmic Reticulum; Endoplasmic Reticulum Chaperone BiP; Enzyme Inhibitors; Eukaryotic Initiation Factor-2; Female; Heat-Shock Proteins; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; In Situ Nick-End Labeling; Membrane Glycoproteins; Mouth Neoplasms; Phosphorylation; Protein Phosphatase 1; Proto-Oncogene Proteins c-akt; Thapsigargin; Thiourea; Tunicamycin; Valproic Acid; Vorinostat

Amlodipine, a dihydropyridine Ca(2+) channel blocker, is reported to inhibit proliferation of human epidermoid carcinoma A431 cells, and specifically attenuates Ca(2+) responses evoked by thapsigargin, an inhibitor of endoplasmic reticulum Ca(2+)-ATPases. In this study, we further examined the possible mechanism of the antiproliferative action of amlodipine and its antitumor effect on A431 xenografts in nude mice. Amlodipine reduced BrdU incorporation into nucleic acids in serum-starved A431 cells, and the reduction was diminished by uridine 5'-triphosphate (UTP), a phospholipase C (PLC)-linked agonist. Fluorometric measurement of intracellular free Ca(2+) concentration revealed that amlodipine blunted the UTP-induced Ca(2+) release from the internal Ca(2+) stores and consequently Ca(2+) influx through Ca(2+)-permeable channels on the plasma membrane. Although amlodipine alone caused Ca(2+) release from thapsigargin-sensitive Ca(2+) stores, such an effect was not reproduced by other dihydropyridine Ca(2+) channel blockers, including nicardipine and nimodipine, despite their antiproliferative effects in the cells. Daily intraperitoneal administration of amlodipine (10 mg/kg) for 20 days into mice bearing A431 xenografts retarded tumor growth and prolonged the survival of mice. Our results suggest a potential antitumor action for amlodipine in vitro and in vivo, which may be in part mediated by inhibiting Ca(2+) influx evoked by the passive depletion of internal Ca(2+) stores and by PLC-linked agonist stimulation.

Topics: Amlodipine; Animals; Antineoplastic Agents; Calcium; Calcium Channel Blockers; Carcinoma, Squamous Cell; Enzyme Inhibitors; Fluorometry; Humans; Male; Mice; Mice, Nude; Nucleic Acid Synthesis Inhibitors; Thapsigargin; Time Factors; Transplantation, Heterologous; Tumor Cells, Cultured; Type C Phospholipases; Uridine Triphosphate

Using patch clamp and ion-selective fluorescence dye techniques, we investigated the influence of actin cytoskeleton rearrangements on the activity of calcium entry channels in plasma membrane of human carcinoma A431 cells. It is shown that disruption of actin microfilaments by cytohalasin D has no significant effect on calcium release from the stores and its entry from the extracellular space. It also does not interfere with the activation of inositol 1,4,5-trisphosphate (IP3)-dependent high-selective low-conductance calcium channels Imin. The treatment of cells with calyculin A induces the formation of actin filament layer beneath plasma membrane and also inhibits Imin activation and calcium entry through the plasma membrane, though calcium efflux from the stores was nearly unchanged. Thus, it is concluded that calcium signalling in A431 cells can be modulated by actin cytoskeleton rearrangements, and may be well described in terms of "conformational coupling" model.

Topics: Actins; Calcium; Calcium Channel Agonists; Calcium Channels; Calcium Signaling; Carcinoma, Squamous Cell; Cell Line; Cell Membrane; Cytochalasin D; Cytoskeleton; Electric Conductivity; Extracellular Space; Humans; Inositol 1,4,5-Trisphosphate; Ion Channel Gating; Marine Toxins; Oxazoles; Patch-Clamp Techniques; Thapsigargin; Tumor Cells, Cultured

The effects of Ca(2+) channel blockers on the proliferation of human epidermoid carcinoma A431 cells were investigated by microtiter tetrazolium (MTT) proliferation assay and bromodeoxyuridine (BrdU) incorporation assay. Dihydropyridine derivatives, such as amlodipine, nicardipine, and nimodipine inhibited A431 cell growth and the incorporation of BrdU into cells with IC(50) values of 20-30 microM, while verapamil, diltiazem and dihydropyridine nifedipine inhibited neither the cell growth nor BrdU incorporation at the same concentration. Though extracellular Ca(2+) is indispensable to the cell growth, an L-type Ca(2+) channel agonist, 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl) phenyl]pyridine-3-carboxylic acid methyl ester (200 nM), did not affect the antiproliferative action of amlodipine. Thapsigargin, an inhibitor of Ca(2+)-ATPase of the endoplasmic reticulum, inhibited itself the growth of A431 cells and also showed a synergistic effect with the antiproliferative action of amlodipine. In the fluorimetric measurement of intracellular free Ca(2+) concentration in fura-2 or fluo-3 loaded A431 cells, amlodipine blunted the thapsigargin- or cyclopiazonic acid-induced Ca(2+) release from endoplasmic reticulum and the ensuing Ca(2+) influx through Ca(2+)-permeable channels. The effect on the thapsigargin-induced Ca(2+) responses could be reproduced by nicardipine and nimodipine but not by nifedipine or verapamil, lacking antiproliferative potency. These findings suggest that the intracellular Ca(2+) control system responsible for thapsigargin- and cyclopiazonic acid-sensitive endoplasmic reticulum, but not L-type Ca(2+) channels, may be modulated by amlodipine, which results in the inhibition of A431 cell growth.

Topics: Calcium; Calcium Channel Blockers; Calcium Channels, L-Type; Carcinoma, Squamous Cell; Cell Division; DNA, Neoplasm; Humans; Inhibitory Concentration 50; Thapsigargin; Time Factors; Tumor Cells, Cultured

Interleukin-1 receptor antagonist (IL-1Ra) is an endogenous inhibitor of interleukin-1. The expression of IL-1Ra and interleukin-1alpha (IL-1alpha) was measured in murine epidermis after treatment with tumor promoters and in tumor cell lines. A single treatment with three different tumor promoters (12-O-tetradecanoylphorbol-13-acetate (TPA), anthralin, and thapsigargin) induced IL-1Ra mRNA with different kinetics in mouse skin. The expression of IL-1Ra mRNA also was induced by TPA and IL-1alpha in a dose-related and time-dependent manner in cultured mouse keratinocytes. Expression of IL-1Ra mRNA peaked 6 h after treatment. Both IL-1Ra and IL-1alpha protein and IL-1Ra and IL-1alpha mRNA were measured in various keratinocyte tumor cell lines (C50, MT1/2, HEL30, JWF2, CH72, and BPCC2). The expression of IL-1alpha was increased in papilloma and squamous cell carcinoma cell lines. IL-1Ra protein also was increased in nontumorigenic and papilloma cell lines; however, the expression was dramatically reduced in some carcinoma cell lines. Finally, we detected IL-1alpha and IL-1Ra protein in mouse skin tumors by western blot analysis, and localization was assessed by immunohistochemical analysis. Positive staining for both IL-1alpha and IL-1Ra was observed in the cytoplasm and was most prominent in the suprabasal layer. Although IL-1Ra protein increased in papillomas and carcinomas, IL-1alpha protein was not significantly increased above basal level in most tumors.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Anthralin; Blotting, Northern; Blotting, Western; Carcinogens; Carcinoma, Squamous Cell; Cell Polarity; Cytoplasm; Disease Progression; Epidermis; Gene Expression Regulation, Neoplastic; Hyperplasia; Inflammation; Interleukin 1 Receptor Antagonist Protein; Interleukin-1; Keratinocytes; Mice; Mice, Inbred SENCAR; Neoplasm Proteins; Papilloma; Precancerous Conditions; RNA, Messenger; RNA, Neoplasm; Sialoglycoproteins; Skin Diseases; Skin Neoplasms; Tetradecanoylphorbol Acetate; Thapsigargin; Tumor Cells, Cultured

Cholera toxin is normally observed only in the Golgi apparatus and not in the endoplasmic reticulum (ER) although the enzymatically active A subunit of cholera toxin has a KDEL sequence. Here we demonstrate transport of horseradish peroxidase-labeled cholera toxin to the ER by electron microscopy in thapsigargin-treated A431 cells. Thapsigargin treatment strongly increased cholera toxin-induced cAMP production, and the formation of the catalytically active A1 fragment was somewhat increased. Binding of cholera toxin to the cell surface and transport of toxin to the Golgi apparatus were not changed in thapsigargin-treated cells, suggesting increased retrograde transport of cholera toxin from the Golgi apparatus to the ER. The data demonstrate that retrograde transport of cholera toxin can take place and that the transport is under regulation. The results are consistent with the idea that retrograde transport can be important for the action of cholera toxin.

Topics: Calcium; Carcinoma, Squamous Cell; Cholera Toxin; Cyclic AMP; Endoplasmic Reticulum; Golgi Apparatus; Humans; Microscopy, Electron; Oligopeptides; Protein Sorting Signals; Thapsigargin; Tumor Cells, Cultured

Depletion of intracellular calcium stores induces transmembrane Ca2+ influx. We studied Ca(2+)- and Ba(2+)-permeable ion channels in A431 cells after store depletion by dialysis of the cytosol with 10 mM BAPTA solution. Cell-attached patches of cells held at low (0.5 microM) external Ca2+ exhibited transient channel activity, lasting for 1-2 min. The channel had a slope conductance of 2 pS with 200 mM CaCl2 and 16 pS with 160 mM BaCl2 in the pipette. Channel activity quickly ran down in excised inside-out patches and was not restored by InsP3 and/or InsP4. Thapsigargin induced activation in cells kept in 1 mM external Ca2+ after BAPTA dialysis. These channels represent one Ca2+ entry pathway activated by depletion of internal calcium stores and are clearly distinct from previously identified calcium repletion currents.

Topics: Barium Compounds; Benzoquinones; Calcium; Calcium Channels; Calcium Chloride; Calcium-Transporting ATPases; Carcinoma, Squamous Cell; Cell Adhesion; Cell Line; Chlorides; Egtazic Acid; Electric Conductivity; Humans; Inositol Phosphates; Ion Channel Gating; Kinetics; Magnesium Chloride; Membrane Potentials; Terpenes; Thapsigargin; Time Factors; Tumor Cells, Cultured