thapsigargin and palytoxin

Palytoxin (PTX) is one of the most potent toxins isolated from marine coelenterates of the genus Palythoa. It induces depolarization in various types of cells by increasing the permeability for monovalent cations. It has been reported that PTX induces endothelium-dependent relaxation of vascular smooth muscle. In this study, we examined the effect of PTX on the cytosolic Ca2+ concentration ([Ca2+]i) in the endothelium of rabbit aortic valves loaded with fluorescent Ca2+ indicators, fura-PE3 or fluo-3. PTX (10 pM-300 nM) irreversibly increased endothelial [Ca2+]i in a concentration-dependent manner. ATP and thapsigargin also increased [Ca2+]i. Imaging of [Ca2+]i with a confocal microscope revealed that PTX increased [Ca2+]i in all endothelial cells studied (n = 13). An inorganic Ca2+ entry blocker, La3+ (30 microM), had no effect on the increase in [Ca2+]i induced by PTX whereas it inhibited the sustained phase of the increase in [Ca2+]i induced by ATP or thapsigargin. The PTX-induced increase in [Ca2+]i was partially inhibited by ouabain and was abolished by removal of external Ca2+ although decrease of Na+ concentration in the incubation medium was ineffective. Activation of protein kinase C by 1 microM 12-deoxyphorbol 13-isobutyrate or inhibition of phosphatase by 10 nM calyculin-A had no effect on the increase in [Ca2+]i induced by PTX, whereas both agents inhibited the sustained phase of the increase in [Ca2+]i induced by ATP or thapsigargin. Mn2+ influx, measured by the quenching of fura-PE3 fluorescence, was accelerated by ATP or thapsigargin, but not by PTX. These results suggest that PTX increases [Ca2+]i in the endothelium of the rabbit aortic valve by increasing Ca2+ influx through a pathway which is different from that activated by ATP or thapsigargin.

Topics: Acrylamides; Adenosine Triphosphate; Animals; Aortic Valve; Calcium; Cnidarian Venoms; Colforsin; Endothelium, Vascular; In Vitro Techniques; Lanthanum; Marine Toxins; Microscopy, Confocal; Ouabain; Oxazoles; Potassium; Rabbits; Sodium; Thapsigargin; Vasoconstrictor Agents

Topics: Acrylamides; Animals; Calcium-Transporting ATPases; Cnidarian Venoms; Enzyme Activation; Ethers, Cyclic; Liver Neoplasms, Experimental; Lyngbya Toxins; Okadaic Acid; Protein Kinase C; Terpenes; Thapsigargin; Tumor Cells, Cultured; Vacuoles

Topics: Acrylamides; Alkaloids; Animals; Carcinogenicity Tests; Carcinogens; Cells, Cultured; Cnidarian Venoms; Enzyme Induction; Ethers, Cyclic; Mice; Okadaic Acid; Ornithine Decarboxylase; Plant Extracts; Plants, Medicinal; Protein Kinase C; Skin; Staurosporine; Tetradecanoylphorbol Acetate; Thapsigargin; Vasoconstrictor Agents

The non-12-O-tetradecanoylphorbol-13-acetate (TPA) type tumor promoters palytoxin and thapsigargin provoked a respiratory burst in porcine and human neutrophils. The amounts of oxygen consumed and superoxide anion (O2-) produced were found to be stoichiometric. Concentrations of 6.5 X 10(-8) M palytoxin and 1.2 X 10(-6) M thapsigargin were required for half-maximal stimulation to 3 X 10(6) porcine cells/ml in Hanks' solution. Combinations of palytoxin and thapsigargin, and of one non-TPA type and one TPA-type tumor promoter, had synergistic effects in stimulating O2- formation in neutrophils, suggesting that these compounds activate the cells by different signal transduction mechanisms.

Topics: Acrylamides; Animals; Carcinogens; Cnidarian Venoms; Humans; In Vitro Techniques; Lyngbya Toxins; NADH, NADPH Oxidoreductases; NADPH Oxidases; Oxygen Consumption; Plant Extracts; Superoxides; Swine; Tetradecanoylphorbol Acetate; Thapsigargin

Ten new tumor promoters which are structurally different from TPA but of similar biological activity were found. Based on their binding to the phorbol ester receptors of cell membranes, these new tumor promoters were classified as TPA-type tumor promoters, teleocidin and aplysiatoxin, which like TPA, activated protein kinase C in vitro, whereas two non-TPA-type tumor promoters, palytoxin and thapsigargin did not induce ODC activity in mouse skin, adhesion of HL-60 cells or activation of protein kinase C, but did show tumor-promoting activity in a two-stage carcinogenesis experiment. Although these two types of tumor promoter exert their tumor-promoting activities through different pathways, production of prostaglandin E2 by rat macrophages was induced by both the TPA-type and non-TPA-type promoters. Therefore, stimulation of arachidonic acid metabolism is suggested to be one of the important biological activities for tumor promotion.

Topics: Acrylamides; Animals; Arachidonic Acid; Arachidonic Acids; Carcinogens; Cnidarian Venoms; Enzyme Activation; Humans; Lyngbya Toxins; Mice; Neoplasms, Experimental; Phorbols; Plant Extracts; Protein Kinase C; Receptors, Cell Surface; Skin Neoplasms; Structure-Activity Relationship; Tetradecanoylphorbol Acetate; Thapsigargin