Biomedical subjects

Hong-Tai Chang

Publications and source records attributed to Hong-Tai Chang.

42 records · Page 3Linked to original sources

PubMed2002

Novel effect of CP55,940, a CB1/CB2 cannabinoid receptor agonist, on intracellular free Ca2+ levels in bladder cancer cells.

The study was undertaken to explore the effect of CP55,940 ((-)-cis-3-[2-Hydroxy4-(1,1-dimethylheptyl) phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol), a drug commonly used as a CB1/CB2 cannabinoid receptor agonist, on intracellular free Ca2+ levels ([Ca2+]i) in several cell types [Ca2+]i was measured in suspended cells by using the fluorescent dye fura-2 as an indicator. At concentrations between 1-50 microM, CP55,940 increased [Ca2+]i in a concentration-dependent manner with an EC50 of 8 microM. The [Ca2+]i signal comprised an initial rise, a slow decay, and a sustained phase. CP55940 (10 microM)-induced (Ca2+]i signal was not altered by 5 microM of two cannabinoid receptor antagonists (AM-251, N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide; AM-281, 1-(2,4-Dichlorophenyl)-5-(4-iodophenyl)-4-m3thyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide). Extracellular Ca2+ removal decreased the maximum value of the Ca2+ signals by 50%. CPS5,940 (10 microM)-induced [Ca2+]i increase in Ca2+-free medium was inhibited by 80% by pretreatment with 1 microM thapsigargin, an endoplasmic reticulum Ca2+ pump inhibitor. Conversely, pretreatment with 10 microM CP55,940 in Ca2+-free medium for 6 min abolished thapsigargin-induced [Ca2+]i increase. Nifedipine (10 microM) and verapamil (10 microM) did not alter CP55,940 (10 microM)-induced [Ca2+]i increase. CP55, 940 (10 microM)-induced Ca2+ release was not affected when phospholipase C was inhibited by 2 microM U73122 (1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione). CP55,940 (5 microM) also increased [Ca22+] in Madin-Darby canine kidney cells, MG63 human osteosarcoma cells, and IMR-32 neuroblastoma cells. Collectively, CP,55940 induced significant [Ca2+]i increases in several cell types by releasing store Ca2+ from thapsigargin-sensitive pools and by causing Ca2+ entry. The CP55,940's action appears to be dissociated from stimulation of cannabinoid receptors

Calcium↗

PubMed2002

Effect of the organotin compound triethyltin on Ca2+ handling in human prostate cancer cells.

The effects of triethyltin on Ca2+ mobilization in human PC3 prostate cancer cells have been explored. Triethyltin increased [Ca2+]i at concentrations larger than 3 microM with an EC50 of 30 microM. Within 5 min, the [Ca2+]i signal was composed of a gradual rise and a sustained phase. The [Ca2+]i signal was reduced by half by removing extracellular Ca2+. The triethyltin-induced [Ca2+]i increases were inhibited by 40% by 10 microM nifedipine, nimodipine and nicardipine, but were not affected by 10 microM of verapamil or diltiazem. In Ca2+-free medium, pretreatment with thapsigargin (1 microM), an endoplasmic reticulum Ca+ pump inhibitor, reduced 200 microM triethyltin-induced Ca+ increases by 50%. Pretreatment with U73122 (2 microM) to inhibit phospholipase C did not alter 200 microM triethyltin-induced [Ca2+]i increases. Incubation with triethyltin at a concentration that did not increase [Ca2+]i (1 microM) in Ca2+-containing medium for 3 min potentiated ATP (10 microM)- or bradykinin (1 microLM)-induced [Ca2+]i increases by 41 +/- 3% and 51 +/- 2%, respectively. Collectively, this study shows that the environmental toxicant triethyltin altered Ca2+ handling in PC3 prostate cancer cells in a concentration-dependent manner: at higher concentrations it increased basal [Ca2+]i; and at lower concentrations it potentiated agonists-induced [Ca2+]i increases.

Calcium↗

PubMed2002

Effect of nordihydroguaiaretic acid on intracellular Ca(2+) concentrations in C6 glioma cells.

The effect of nordihydroguaiaretic acid (NDGA) on Ca(2+) signaling in C6 glioma cells has been investigated. NDGA (5-100 microM) increased [Ca(2+)]i concentration-dependently. The [Ca(2+)]i increase comprised an initial rise and an elevated phase over a time period of 4 min. Removal of extracellular Ca(2+) reduced NDGA-induced [Ca(2+)]i signals by 52+/-2%. After incubation of cells with NDGA in Ca(2+)-free medium for 4 min, addition of 3 mM CaCl2 induced a concentration-dependent increase in [Ca(2+)]i. NDGA (100 microM)-induced [Ca(2+)]i increases in Ca(2+)-containing medium was not changed by pretreatment with 10 microM nifedipine or verapamil. In Ca(2+)-free medium, pretreatment with the endoplasmic reticulum Ca(2+) pump inhibitor thapsigargin (1 microM) abolished 100 microM NDGA-induced [Ca(2+)]i increases. Inhibition of phospholipase C with 2 microM U73122 had little effect on 100 microM NDGA-induced Ca(2+) release. Several other lipoxygenase inhibitors had no effect on basal [Ca(2+)]i. Collectively, the results suggest that NDGA increased [Ca(2+)]i in glioma cells in a lipoxygenase-independent manner, by releasing Ca(2+) from the endoplasmic reticulum in a manner independent of phospholipase C activity and by causing Ca(2+) influx.

Animals↗

PubMed2002

Tamoxifen-induced increases in cytoplasmic free Ca2+ levels in human breast cancer cells.

Tamoxifen has been shown to increase cytoplasmic free Ca2+ levels [Ca2+]i in renal tubular cells and bladder cancer cells, and to after Ca2+ signaling in MCF-7 breast cancer cells. The present study examined the effect of tamoxifen on [Ca2+], in ZR-75-1 human breast cancer cells using fura-2 as an indicator. Tamoxifen increased [Ca2+]i at a concentration above 2 microM with an EC50 of 5 microM. Removing extracellular Ca2+ reduced the response by 48+/-2%. In Ca2+-free medium, after tamoxifen-induced [Ca2+]i increased had returned to baseline, adding 3 mM Ca2+ increased [Ca2+]i in a concentration-dependent manner. Further, pretreatment with 10 microM tamoxifen abolished the [Ca2+]i increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor); and conversely, pretreatment with thapsigargin prevented tamoxifen from releasing more Ca2+. Tamoxifen (10 microM)-induced Ca2+ release was not changed by inhibiting phospholipase C activity with 2 microM U73122. Trypan blue exclusion assay revealed that tamoxifen (1-10 microM) did not alter viability after 1 min of incubation, but killed 10% of cells after 3-10 min of incubation. Together, this study shows that tamoxifen (>2 microM) induced a significant, immediate increase in [Ca2+]i in ZR-75-1 breast cancer cells. Tamoxifen acted by releasing Ca2+ from the endoplasmic reticulum Ca2+ stores in a manner independent of phospholipase C activity, and by inducing Ca2+ entry from extracellular medium. Tamoxifen may be of mild cytotoxicity after acute exposure.

Breast Neoplasms↗

PubMed2002

Effect of the anti-breast cancer drug tamoxifen on Ca(2+) movement in human osteosarcoma cells.

The anti-breast cancer drug tamoxifen has recently been shown to cause an increase in [Ca(2+)]i in renal tubular cells, breast cells and bladder cells. Because tamoxifen is known to interact with oestrogens leading to modulation of bone metabolism, the present study was aimed at exploring whether tamoxifen could alter Ca(2+) signaling in human osteoblast-like MG63 cells. Cytosolic free Ca(2+) levels were recorded by using the Ca(2+)-sensitive dye fura-2. Tamoxifen induced a sustained [Ca(2+)]i increase at concentrations above 1 microM with an EC(50) of 8 microM. Removal of extracellular Ca(2+) reduced the response by 40%, suggesting that tamoxifen induced both Ca(2+) influx and store Ca(2+) release. Tamoxifen-induced Ca(2+) influx was confirmed as tamoxifen caused Mn(2+) influx-induced quench of fura-2 fluorescence. In Ca(2+)-free medium, pretreatment with 10 microM tamoxifen abolished the [Ca(2+)]i increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor), and by 2 microM carbonylcyanide m-chlorophenylhydrazone (a mitochondrial uncoupler). Conversely, pretreatment with thapsigargin and carbonylcyanide m-chlorophenylhydrazone only reduced 64% of tamoxifen-induced [Ca(2+)]i increases. Addition of 2 microM U73122 to inhibit phospholipase C activity abolished the [Ca(2+)]i increase induced by 1 microM histamine, a phospholipase C-dependent Ca(2+) mobilizer, without affecting 10 microM tamoxifen-induced Ca(2+) release. The [Ca(2+)]i increase induced by 10 microM tamoxifen was not altered by 10 microM of nifedipine, verapamil and diltiazem. Together, the data show that tamoxifen induced a lasting increase in [Ca(2+)]i in human osteoblast-like cells by causing Ca(2+) influx and releasing Ca(2+) from multiple stores in a phospholipase C-independent manner.

Antineoplastic Agents↗

PubMed2002

Effect of riluzole on cytosolic Ca2+ increase in human osteosarcoma cells.

In human osteosarcoma MG63 cells, the effect of the neuroprotective drug riluzole on the intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured using fura-2. Riluzole (50-500 micromol/l) caused a rapid and sustained plateau increase in [Ca(2+)](i) in a concentration-dependent manner (EC(50) = 150 micromol/l). The riluzole-induced rise in [Ca(2+)](i) was prevented by 58 and 20% by extracellular Ca(2+) removal and nifedipine, respectively, but was not changed by La(3+) and verapamil. In Ca(2+)-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum (ER) Ca(2+)-ATPase, caused a monophasic increase in [Ca(2+)](i), after which the increasing effect of riluzole on [Ca(2+)](i) was attenuated by 84%; also, pretreatment with riluzole abolished the thapsigargin-induced [Ca(2+)](i) increase. U73122, an inhibitor of phospholipase C, abrogated the ATP (but not riluzole)-induced rise in [Ca(2+)](i). A low concentration (6 micromol/l) of riluzole selectively potentiated the bradykinin (but not ATP and histamine)-induced increase in [Ca(2+)](i). These results suggest that riluzole rapidly increases [Ca(2+)](i) by stimulating both the extracellular Ca(2+) influx via a nifedipine-sensitive pathway and intracellular Ca(2+) release from the ER via an as yet unidentified mechanism(s).

Calcium↗