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The effects of five lignans (epi-aschantin, epi-magnolin, epi-yangambin, deoxypodophyllotoxin, yatein) isolated from Hernandia nymphaeifolia (Presl.) Kubitzki (Hernandiaceae) on intracellular Ca2+ levels ([Ca2+]i) in human neutrophils were investigated by using fura-2 as a fluorescent probe. In both Ca2+-containing and Ca2+-free media, the lignans (50-100 microM) did not alter basal [Ca2+]i but inhibited the [Ca2+]i increase induced by platelet activating factor (PAF, 10 microM), leukotriene B4 (LTB4, 0.2 microM), and thapsigargin (1 microM) to different extents. In Ca2+-free medium, after depleting stores of Ca2+ with PAF, LTB4 or thapsigargin, addition of 3 mM Ca2+ induced Ca2+ influx. Each of the lignans (50-100 microM) caused 39-89% inhibition of PAF-induced Ca2+ influx; whereas only epi-aschantin was able to inhibit LTB4- and thapsigargin-induced Ca2+ influx by 54-79%. Together, the results suggest that in human neutrophils, these lignans did not alter basal [Ca2+]i but inhibited Ca2+ movement induced by Ca2+ mobilizing agents.

In Madin-Darby canine kidney (MDCK) cells, the effect of maprotiline, an antidepressant, on intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured using fura-2. Maprotiline (2.5 microM) caused a rapid rise of [Ca(2+)](i) in a concentration-dependent manner (EC(50) 200 microM). Maprotiline-induced [Ca(2+)](i) rise was reduced by removal of extracellular Ca(2+) or by addition of La(3+), but was not altered by voltage-gated Ca(2+)-channel blockers. Maprotiline-induced Mn(2+) influx-associated fura-2 fluorescence quench directly suggests that maprotiline caused Ca(2+) influx. In Ca(2+)-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, caused a monophasic [Ca(2+)](i) rise, after which the increasing effect of maprotiline on [Ca(2+)](i) was nearly abolished; also, pretreatment with maprotiline reduced a portion of thapsigargin-induced [Ca(2+)](i) rise. U73122, an inhibitor of phospholipase C, abolished [Ca(2+)](i) rise induced by ATP (but not by maprotiline). Overnight incubation with 1-10 microM maprotiline enhanced cell viability, but 20-50 microM maprotiline decreased it. These findings suggest that maprotiline rapidly increases [Ca(2+)](i) in renal tubular cells by stimulating both extracellular Ca(2+) influx and intracellular Ca(2+) release, and may modulate cell proliferation in a concentration-dependent manner.

The effect of oxidants on Ca(2+) movement in osteoblasts is unclear. In this study, we show that 4,4'-dithiodipyridine (4,4'-DTDP), a reactive disulphide that mobilizes Ca(2+) in muscle, induces an increase in cytoplasmic free-Ca(2+) concentrations ([Ca(2+)](i)) in MG63 human osteosarcoma cells loaded with the Ca(2+)-sensitive dye fura-2. 4,4'-DTDP acted in a concentration-dependent manner with an EC(50) of 10 microM. Removing extracellular Ca(2+) reduced the Ca(2+) signal by 35%. In Ca(2+)-free medium, the 4,4'-DTDP-induced [Ca(2+)](i) increase was not changed by depleting store Ca(2+) with 50 microM brefeldin A (a Golgi apparatus permeabilizer), by 2 microM carbonylcyanide m-chlorophenylhydrazone (CCCP, a mitochondrial uncoupler), by 1 microM thapsigargin (an inhibitor of the endoplasmic reticulum Ca(2+) pump) or by 5 microM ryanodine. Ca(2+) signals induced by 4,4'-DTDP in Ca(2+)-containing medium were not affected by modulation of protein kinase C activity or suppression of phospholipase C activity. However, 4,4'-DTDP-induced Ca(2+) release was inhibited by a thiol-selective reducing reagent, dithiothreitol (0.05-2.5 mM), in a concentration-dependent manner. Collectively, this study shows that 4,4'-DTDP induced [Ca(2+)](i) increases in human osteosarcoma cells via releasing store Ca(2+) from multiple stores in a manner independent of protein kinase C or phospholipase C activity. The store Ca(2+) release induced by 4,4'-DTDP appears to be associated with thiol oxidation. Furthermore, overnight incubation with 4,4'-DTDP inhibited cell activity in a concentration-dependent manner.