Xestospongin C, a novel blocker of IP3 receptor, attenuates the increase in cytosolic calcium level and degranulation that is induced by antigen in RBL-2H3 mast cells.
1. We evaluated the role of the cross-linking of Fc epsilon RI-mediated inositol 1,4,5-triphosphate (IP(3)) in the increase in cytosolic Ca(2+) level ([Ca(2+)](i)) using xestospongin C, a selective membrane permeable blocker of IP(3) receptor, in RBL-2H3 mast cells. 2. In the cells sensitized with anti-dinitrophenol (DNP) IgE, DNP-human serum albumin (DNP-HSA) and thapsigargin induced degranulation of beta-hexosaminidase and a sustained increase in [Ca(2+)](i). Xestospongin C (3 - 10 microM) inhibited both of these changes that were induced by DNP-HSA without changing those induced by thapsigargin. 3. In the absence of external Ca(2+), DNP-HSA induced a transient increase in [Ca(2+)](i). Xestospongin C (3 - 10 microM) inhibited this increase in [Ca(2+)](i). 4. In the cells permeabilized with beta-escin, the application of IP(3) decreased Ca(2+) in the endoplasmic reticulum (ER) as evaluated by mag-fura-2. Xestospongin C (3 - 10 microM) inhibited the effect of IP(3). 5. After the depletion of Ca(2+) stores due to stimulation with DNP-HSA or thapsigargin, the addition of Ca(2+) induced capacitative calcium entry (CCE). Xestospongin C (3 - 10 microM) inhibited the DNP-HSA-induced CCE, whereas it did not affect the thapsigargin-induced CCE. 6. These results suggest that Fc epsilon RI-mediated generation of IP(3) contributes to Ca(2+) release not only in the initial phase but also in the sustained phase of the increase in [Ca(2+)](i), resulting in prolonged Ca(2+) depletion in the ER. The ER Ca(2+) depletion may subsequently activate CCE to achieve a continuous [Ca(2+)](i) increase, which is necessary for degranulation in the RBL-2H3 mast cells. Xestospongin C may inhibit Ca(2+) release and consequently may attenuate degranulation.
Oka
Tatsuya
T
Department of Veterinary Pharmacology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-Ku, Tokyo 113-8657, Japan.
Sato
Koichi
K
Hori
Masatoshi
M
Ozaki
Hiroshi
H
Karaki
Hideaki
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D015550:Cell Degranulation / Q000187:drug effects*; D002463:Cell Membrane Permeability / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D004140:Dinitrophenols / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D004928:Escin / Q000494:pharmacology; D006241:Haptens / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism* / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D047028:Macrocyclic Compounds; D008407:Mast Cells / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010080:Oxazoles / Q000494:pharmacology*; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012709:Serum Albumin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D001619:beta-N-Acetylhexosaminidases / Q000037:antagonists & inhibitors / Q000378:metabolism
D015220:Calcium Channels; D004140:Dinitrophenols; D006241:Haptens; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D047028:Macrocyclic Compounds; D010080:Oxazoles; D018160:Receptors, Cytoplasmic and Nuclear; D012709:Serum Albumin; C058064:dinitrophenyl-human serum albumin conjugate; C108644:xestospongin A; D004928:Escin; D015544:Inositol 1,4,5-Trisphosphate; D001619:beta-N-Acetylhexosaminidases; D002118:Calcium