Li-Ling Tseng

Mechanisms of histamine-induced intracellular Ca2+ release and extracellular Ca2+ entry in MG63 human osteosarcoma cells

The effect of histamine on intracellular free Ca2+ levels ([Ca2+](i)) in MG63 human osteosarcoma cells was explored using fura-2 as a Ca2+ dye. Histamine increased ([Ca2+](i)) in a concentration-dependent fashion with an EC(50) value of 0.5 microM. Extracellular Ca2+ removal inhibited the ([Ca2+](i)) signals. Histamine failed to increase ([Ca2+](i)) in Ca2+-free medium after cells were pretreated with thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor). Addition of Ca2+ induced concentration-dependent ([Ca2+](i)) increases after preincubation with histamine in Ca2+-free medium. Histamine-induced intracellular Ca2+ release was abolished by inhibiting phospholipase C with 1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). The ([Ca2+](i)) increase induced by histamine in Ca2+ medium was abolished by cimetidine, but was not altered by pyrilamine, nifedipine, verapamil, and La(3+). Together, this study shows that histamine increased in ([Ca2+](i)) in osteosarcoma cells by stimulating H2 histamine receptors. The Ca2+ signal was caused by Ca2+ release from the endoplasmic reticulum in a phospholipase C-dependent manner. The Ca2+ release was accompanied by Ca(2+) influx.

Effect of betulinic acid on intracellular-free Ca2+ levels in Madin Darby canine kidney cells

The effect of betulinic acid, an anti-tumor and apoptosis-inducing natural product, on intracellular-free levels of Ca(2+) ([Ca(2+)](i)) in Madin Darby canine kidney (MDCK) cells was examined by using fura-2 as a Ca(2+) dye. Betulinic acid caused significant increases in [Ca(2+)](i) concentration dependently between 25 and 500 nM with an EC(50) of 100 nM. The [Ca(2+)](i) signal was composed of an initial gradual rise and a plateau. The response was decreased by removal of extracellular Ca(2+) by 45+/-10%. In Ca(2+)-free medium, pretreatment with 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor) abolished 250 microM betulinic acid-induced [Ca(2+)](i) increases. Conversely, pretreatment with betulinic acid only partly inhibited thapsigargin-induced [Ca(2+)](i) increases. Addition of 3 mM Ca(2+) induced a [Ca(2+)](i) increase after pretreatment with 250 nM betulinic acid in Ca(2+)-free medium for 5 min. This [Ca(2+)](i) increase was not altered by the addition of 20 microM SKF96365 and 10 microM econazole. Inhibiting inositol 1,4,5-trisphosphate formation with the phospholipase C inhibitor U73122 (2 microM) abolished 250 nM betulinic acid-induced Ca(2+) release. Pretreatment with 10 microM La(3+) inhibited 250 nM betulinic acid-induced [Ca(2+)](i) increases by 85+/-3%; whereas 10 microM of verapamil, nifedipine and diltiazem had no effect. In Ca(2+) medium, pretreatment with 2.5 nM betulinic aid for 260 s potentiated 10 microM ATP and 1 microM thapsigargin-induced [Ca(2+)](i) increases by 33+/-3% and 45+/-3%, respectively. Trypan blue exclusion revealed that acute exposure of 250 nM betulinic acid for 2-30 min decreased cell viability by 6+/-2%, which could be prevented by pretreatment with 2 microM U731222. Together, the results suggest that betulinic acid induced significant [Ca(2+)](i) increases in MDCK cells in a concentration-dependent manner, and also induced mild cell death. The [Ca(2+)](i) signal was contributed by an inositol 1,4, 5-trisphosphate-dependent release of intracellular Ca(2+) from thapsigargin-sensitive stores, and by inducing Ca(2+) entry from extracellular medium in a La(3+)-sensitive manner.

Mechanisms of diethylstilbestrol-induced calcium movement in MG63 human osteosarcoma cells.

The effect of the estrogen diethylstilbestrol (DES) on cytosolic free Ca(2+) levels ([Ca(2+)](i)) in MG63 human osteoblasts was explored by using fura-2 as a Ca(2+) indicator. DES at concentrations between 5--20 microM induced an immediate increase in [Ca(2+)](i) in a concentration-dependent manner with an EC(50) of 10 microM. Removing extracellular Ca(2+) reduced the Ca(2+) signal by 70%. Pretreatment with 50 microM La(3+) or 10 microM of nifedipine, verapamil and diltiazem did not change 20 microM DES-induced [Ca(2+)](i) increases. Addition of 3 mM Ca(2+) increased [Ca(2+)](i) in cells pretreated with 20 microM DES in Ca(2+)-free medium. Pretreatment with 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor) to deplete the endoplasmic reticulum Ca(2+) store partly inhibited 20 microM DES-induced Ca(2+) release, but addition of carbonylcyanide m-chlorophenylhydrazone (CCCP; a mitochondrial uncoupler) and thapsigargin together abolished DES-induced Ca(2+) release. Conversely, pretreatment with 20 microM DES abrogated CCCP- and thapsigargin-induced Ca(2+) release. Inhibition of phospholipase C activity with 2 microM U73122 did not alter 20 microM DES-induced Ca2+ release. Another estrogen 17beta-estradiol also increased [Ca(2+)](i) in a concentration-dependent manner with an EC50 of 7 microM. Together, the data indicate that in human osteoblasts, DES increased [Ca(2+)](i) via causing Ca(2+) release from both mitochondria and the endoplasmic reticulum in a phospholipase C-independent manner, and by causing Ca(2+) influx.

Effect of the Antidepressant Desipramine on Cytosolic Ca2+ Movement and Proliferation in Human Osteosarcoma Cells

In human osteosarcoma MG63 cells, the effect of desipramine, an antidepressant, on intracellular Ca²⁺ concentration ([Ca²⁺]_i) was measured by using fura-2. Desipramine (>10 µmol/l) caused a rapid and sustained rise of [Ca²⁺]_i in a concentration-dependent manner (EC₅₀ = 200 µmol/l). Desipramine-induced [Ca²⁺]_i rise was prevented by 80% by removal of extracellular Ca²⁺ but was not altered by voltage-gated Ca²⁺ channel blockers. In Ca²⁺-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum (ER) Ca²⁺-ATPase, caused a monophasic [Ca²⁺]_i rise, after which the increasing effect of desipramine on [Ca²⁺]_i was abolished; also, pretreatment with desipramine partly reduced thapsigargin-induced [Ca²⁺]_i increase. U73122, an inhibitor of phospholipase C, did not affect desipramine-induced [Ca²⁺]_i rise. Overnight incubation with 10 µmol/l desipramine did not alter cell proliferation, but killed 32 and 89% of cells at concentrations of 100 and 200 µmol/l, respectively. These findings suggest that desipramine rapidly increases [Ca²⁺]_i in osteoblasts by stimulating both extracellular Ca²⁺ influx and intracellular Ca²⁺ release, and is cytotoxic at high concentrations.

CP55,940 increases intracellular Ca2+ levels in Madin-Darby canine kidney cells

The effect of CP55,940, a presumed CB1/CB2 cannabinoid receptor agonist, on intracellular free Ca2+ levels ([Ca2+]i) in Madin-Darby canine kidney cells was examined by using the fluorescent dye fura-2 as a Ca2+ indicator. CP55,940 (2-50 microM) increased [Ca2+]i concentration-dependently with an EC50 of 8 microM. The [Ca2+]i signal comprised an initial rise and a sustained phase. Extracellular Ca2+ removal decreased the maximum [Ca2+]i signals by 32+/-12%. CP55,940 (20 microM)-induced [Ca2+]i signal was not altered by 5 microM of two cannabinoid receptor antagonists, AM-251 and AM-281. CP55,940 (20 microM)-induced [Ca2+]i increase in Ca2+-free medium was inhibited by 86+/-3% by pretreatment with 1 microM thapsigargin, an endoplasmic reticulum Ca2+ pump inhibitor. Conversely, pretreatment with 20 microM CP55,940 in Ca2+-free medium for 6 min abolished thapsigargin-induced [Ca2+]i increases. CP55,940 (20 microM)-induced intracellular Ca2+ release was not inhibited when inositol 1,4,5-trisphosphate formation was abolished by suppressing phospholipase C with 2 microM U73122. Collectively, this study shows that CP,55940 induced significant [Ca2+]i increases in canine renal tubular cells by releasing stored Ca2+ from the thapsigargin-sensitive pools in an inositol 1,4,5-trisphosphate-independent manner, and also by causing extracellular Ca2+ entry. The CP55,940s action appears to be dissociated from stimulation of cannabinoid receptors.

NPC-14686, a novel anti-inflammatory agent, increased intracellular Ca2+ concentrations in MDCK renal tubular cells

The effect of NPC-14686 (Fmoc-L-homophenylalanine), a novel anti-inflammatory agent on intracellular free Ca(2+) concentrations ([Ca(2+)](i)) in Madin Darby canine kidney (MDCK) renal tubular cells, was investigated, using fura-2 as a Ca(2+) dye. At concentrations between 10 and 200 microM NPC-14686 increased [Ca(2+)](i) concentration dependently. The [Ca(2+)](i) signal comprised an initial rise and a sustained phase. Ca(2+) removal inhibited the Ca(2+) signals by 90%. In Ca(2+)-free medium, pretreatment with 100 microM NPC-14686 nearly abolished the [Ca(2+)](i) increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor) and abolished the [Ca(2+)](i) increase induced by 2 microM carbonylcyanide m-chlorophenylhydrazone (CCCP) (a mitochondrial uncoupler). NPC-14686 (100 microM) induced a slight [Ca(2+)](i) increase after pretreatment with 2 microM CCCP and 1 microM thapsigargin. Addition of 3 mM Ca(2+) elicited a [Ca(2+)](i) increase in cells pretreated with 100 microM NPC-14686 in Ca(2+)-free medium. Inhibition of inositol-1,4,5-trisphosphate (IP(3)) production by suppressing phospholipase C with 2 microM U73122 did not alter NPC-14686-induced Ca(2+) release. Trypan blue exclusion revealed that incubation with 10 or 200 microM NPC-14686 for 1-30 min decreased cell viability by 10-20% concentration dependently. Collectively, the results demonstrate that, in MDCK tubular cells, NPC-14686 induced Ca(2+) release followed by Ca(2+) entry, with the latter playing a major role. NPC-14686 appears to release intracellular Ca(2+) in an IP(3)-uncoupled manner. NPC-14686 may be of mild cytotoxicity.

Effect of sertraline on [Ca2+]i and viability of human MG63 osteosarcoma cells

The antidepressant, sertraline, has been shown to have diverse in vitro effects. This study examined whether sertraline altered [Ca2+]i in MG63 human osteosarcoma cells by using fura-2 as a Ca2+-sensitive fluorescent dye. At 50–200 µM, sertraline induced a [Ca2+]i rise in a concentration-dependent manner. Ca2+ response was decreased by removing extracellular Ca2+, suggesting that Ca2+ entry and release contributed to the [Ca2+]i signal. Sertraline-induced Ca2+ entry was inhibited by nifedipine, La3+, Gd3+, and SK&F96365. When extracellular Ca2+ was removed, pretreatment with the endoplasmic reticulum (ER) Ca2+ pump inhibitor, thapsigargin, or 2,5-di-tert-butylhydroquinone (BHQ) abolished the sertraline-evoked [Ca2+]i rise. Incubation with sertraline also abolished the thapsigargin or BHQ-induced [Ca2+]i rise. Inhibition of phospholipase C (PLC) with U73122 abolished the sertraline-induced [Ca2+]i rise. At 20–30 µM, overnight treatment with sertraline killed cells in a concentration-dependent manner. The cytotoxic effect of sertraline was not reversed by chelating cytosolic Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA). Annexin V/propidium iodide staining data demonstrate that sertraline (30 µM) evoked apoptosis. Sertraline (20 and 30 µM) also increased levels of reactive oxygen species. Together, in human osteosarcoma cells, sertraline evoked a [Ca2+]i rise by inducing PLC-dependent Ca2+ release from the ER and Ca2+ entry by L-type Ca2+ channels and store-operated Ca2+ channels. Sertraline induced cell death that may involve apoptosis by mitochondrial pathways.

The anti-anginal drug fendiline increases intracellular Ca2+ levels in MG63 human osteosarcoma cells

The effect of fendiline, an anti-anginal drug, on cytosolic free Ca(2+) levels ([Ca(2+)](i)) in MG63 human osteosarcoma cells was explored by using fura-2 as a Ca(2+) indicator. Fendiline at concentrations between 1 and 200 microM increased [Ca(2+)](i) in a concentration-dependent manner and the signal saturated at 100 microM. The Ca(2+) signal was inhibited by 65+/-5% by Ca(2+) removal and by 38+/-5% by 10 microM nifedipine, but was unchanged by 10 microM La(3+) or verapamil. In Ca(2+)-free medium, pre-treatment with 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor) to deplete the endoplasmic reticulum Ca(2+) store inhibited fendiline-induced intracellular Ca(2+) release. The Ca(2+) release induced by 50 microM fendiline appeared to be independent of IP(3) because the [Ca(2+)](i) increase was unaltered by inhibiting phospholipase C with 2 microM U73122. Collectively, the results suggest that in MG63 cells fendiline caused an increase in [Ca(2+)](i) by inducing Ca(2+) influx and Ca(2+) release in an IP(3)-independent manner.

Effect of Methoxychlor on Ca2+ Handling and Viability in OC2 Human Oral Cancer Cells

Abstract:  The effect of the insecticide methoxychlor on the physiology of oral cells is unknown. This study aimed to explore the effect of methoxychlor on cytosolic Ca2+ concentrations ([Ca2+]i) in human oral cancer cells (OC2) by using the Ca2+‐sensitive fluorescent dye fura‐2. Methoxychlor at 5–20 μM increased [Ca2+]i in a concentration‐dependent manner. The signal was reduced by 70% by removing extracellular Ca2+. Methoxychlor‐induced Ca2+ entry was not affected by nifedipine, econazole, SK&F96365 and protein kinase C modulators but was inhibited by the phospholipase A2 inhibitor aristolochic acid. In Ca2+‐free medium, treatment with the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin or 2,5‐di‐tert‐butylhydroquinone (BHQ) inhibited or abolished methoxychlor‐induced [Ca2+]i rise. Incubation with methoxychlor also inhibited thapsigargin‐ or BHQ‐induced [Ca2+]i rise. Inhibition of phospholipase C with U73122 did not alter methoxychlor‐induced [Ca2+]i rise. At 5–20 μM, methoxychlor killed cells in a concentration‐dependent manner. The cytotoxic effect of methoxychlor was not reversed by chelating cytosolic Ca2+ with 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N’,N’‐tetraacetic acid/AM (BAPTA/AM). Annexin V‐FITC data suggest that methoxychlor (10 and 20 μM) evoked apoptosis in a concentration‐dependent manner. Together, in human OC2, methoxychlor induced a [Ca2+]i rise probably by inducing phospholipase C‐independent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via phospholipase A2‐sensitive channels. Methoxychlor induced cell death that may involve apoptosis.

Effect of 17β-Estradiol on Intracellular Ca2+ Levels in Renal Tubular Cells

The effect of 17β-estradiol on intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in Madin Darby canine kidney cells was investigated by using the fluorescent dye fura-2. 17β-Estradiol (5–100 µmol/l) induced instantaneous increases in [Ca²⁺]_i in a concentration-dependent manner. Ca²⁺ removal inhibited 45 ± 15% of the Ca²⁺ signal. In Ca²⁺-free medium, pretreatment with 50 µmol/l 17β-estradiol abolished the [Ca²⁺]_i increases induced by 2 µmol/l carbonylcyanide m-chlorophenylhydrazone (CCCP; a mitochondrial uncoupler), 1 µmol/l thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor) and 50 µmol/l brefeldin A (an antibiotic which disperses the Golgi complex), but pretreatment with brefeldin A, CCCP and thapsigargin only partly inhibited the 17β-estradiol-induced [Ca²⁺]_i signal. Adding 3 mmol/lCa²⁺ increased [Ca²⁺]_i in cells pretreated with 5–100 µmol/l 17β-estradiol in Ca²⁺-free medium. Pretreatment with 1 µmol/l U73122 to abolish the formation of inositol-1,4,5-trisphosphate inhibited 50% of the Ca²⁺ release induced by 50 µmol/l 17β-estradiol. 17β-Estradiol (20 µmol/l) also increased [Ca²⁺]_i in human bladder cancer cells and prostate cancer cells. Collectively, this study shows that 17β-estradiol evoked a significant internal Ca²⁺ release and external Ca²⁺ entry possibly in a nongenomic manner.