In recent immunological studies, it has been suggested that trichloroethylene (TCE) participates in the onset of pneumatosis cystoides intestinalis (PCI) through a certain mechanism; however, the mechanism by which it develops remains unknown. Based on findings that secondary PCI is often linked with autoimmune disease, the possibility that some genetic or immunological mechanisms are involved in the development of PCI has been proposed. Pneumatosis cystoides intestinalis is not a type of disease where a dose-response relationship with TCE exposure can be recognized and it is difficult to reproduce its physiopathology through TCE exposure in ordinary experimental animals. In the present study, immunological changes caused by TCE exposure were investigated by employing MRL-lpr/lpr mice that are genetically labile to autoimmune diseases. To observe changes in B cell functions, serum antibody titres were measured; and for the T cell function, T cell subsets were examined. The animals were exposed to TCE at dosages of 0, 500, 1000 and 2000 ppm through inhalation 4 h a day, 6 days a week, for 8 weeks. It was found that only IgG production capacity was suppressed and there were no changes in T cell subsets with TCE concentrations up to 1000 ppm. At a concentration of 2000 ppm, changes were noted in both T and B cell functions. Typical organs that are responsible for immunological functions were examined for their morphological changes under a light microscope: the spleen and liver exhibited dose-response changes at a concentration of 500 ppm or greater. The development of immunoblastoid cells at a concentration of 1000 ppm indicated a possibility that a change has occurred in the immunological system. These findings show that exposure to TCE at high concentrations affects the immune system, but the study failed to induce PCI in the experimental animals. Further studies on TCE exposure at lower concentrations for longer periods are needed.

Anesthetics, Inhalation↗

PubMedDate not supplied

Role of microtubules on Ca2+ release from the endoplasmic reticulum and associated histamine release from rat peritoneal mast cells.

In order to study the role of cytoskeletons on histamine release from mast cells, the effects of cytoskeleton-inhibiting agents were investigated. Since neither colchicine, vinblastine nor cytochalasin D was effective in inhibiting the IP3 formation, it is possible that neither microtubules nor microfilaments of rat peritoneal mast cells participate in the initial membrane events of the histamine release. However, both colchicine and vinblastine, but not cytochalasin D, were effective in inhibiting Ca2+ release from the intracellular Ca store. It was accordingly suggested that the microtubules, rather than microfilaments, are intimately related to the Ca2+ releasing process from the endoplasmic reticulum. The fluorescence intensity of the mast cells stained with FITC-labeled anti-tubulin antibody reflects the amount of tubulin polymers inside the cell, and colchicine treatment decreased the fluorescence intensity, indicating that colchicine is effective in depolymerizing the microtubules of rat mast cells. By contrast, the amount of tubulin polymer in the mast cells increased by compound 48/80, indicating that the rearrangement of microtubules took place in the mast cells, leading to histamine release. When permeabilized mast cells were exposed to potassium antimonate solution, microtubules attached themselves to the endoplasmic reticulum and many Ca antimonate dots were observed. From the present results, it was concluded that microtubules play an important role in the processes leading to Ca2+ release from the intracellular Ca store and subsequent histamine release.

Animals↗

PubMedDate not supplied

Ca uptake and Ca releasing properties of the endoplasmic reticulum in rat peritoneal mast cells.

In order to study the characteristics of the intracellular Ca store of mast cells, organelles of rat peritoneal mast cells were fractionated. The binding of 45Ca was at its peak in the fractions where the highest activity of glucose-6-phosphatase, the marker enzyme for the endoplasmic reticulum (ER), was measured. The ER-rich fraction exhibited an ATP-dependent uptake of 45Ca and this uptake was inhibited by pretreatment with ATPase inhibitors such as LaCl3 or Na3VO4. When inositol 1,4,5-trisphosphate (IP3) was added to a medium containing the 45Ca-loaded ER fraction, it caused a dose-dependent release of 45Ca at concentrations higher than 0.5 microM, while inositol 1-monophosphate and inositol 1,4-bisphosphate were not effective even at higher concentrations. The results of a binding assay using 3H-labeled IP3 indicated that there exist two kinds of IP3 binding site in the ER: one is of high affinity but low capacity while the other is of low affinity and high capacity. IP3-induced 45Ca release was dose-dependently inhibited by pretreatment with c-AMP. The present study supports the assumption that the intracellular Ca store associated with histamine release from the mast cell is the ER.

Adenosine Triphosphate↗

PubMedDate not supplied

Histamine release from beta-escin-permeabilized rat peritoneal mast cells and its inhibition by intracellular Ca2+ blockers, calmodulin inhibitors and cAMP.

In order to study the intracellular events leading to histamine release, rat peritoneal mast cells were permeabilized using beta-escin, a triterpenoid. IP3 (0.5-10 microM) dose-dependently elicited significant histamine release from permeabilized mast cells in a Ca2+-free medium, as did GTP-gamma-S at concentrations higher than 5 microM, GTP-gamma-S induced IP3 production dose-dependently in association with histamine release. Histamine release induced by IP3 and GTP-gamma-S was inhibited by pretreatment with TMB-8, while neomycin pretreatment suppressed histamine release caused by GTP-gamma-S but not that caused by IP3.IP3 may cause Ca2+ release from the intracellular Ca2+ store as the key event leading to histamine release. At concentrations higher than 0.1 microM, Ca2+ dose-dependently induced histamine release. Both IP3-and Ca2+-induced histamine release from permeabilized mast cells was inhibited by pretreatment with calmodulin inhibitors (W-7 and calmidazolium), or with cytochalasin D or colchicine. Pretreatment with cAMP also inhibited the histamine release induced by either IP3 or Ca2+. From the present study, it can be assumed that (1) Ca2+ may act on a calmodulin-associated process(es) and cytoskeletal systems, in the process leading to histamine release, and (2) cAMP seems to inhibit histamine release, even in the stages following Ca2+ release from the intracellular Ca2+ store.

Animals↗

PubMedDate not supplied

Role of endoplasmic reticulum, an intracellular Ca2+ store, in histamine release from rat peritoneal mast cell.

By means of the Ca-antimonate precipitation technique, it was revealed that Ca2+ accumulates in the endoplasmic reticulum (ER) of rat peritoneal mast cells. The ER of rat mast cells was isolated using Percoll density gradient centrifugation, and its characteristics were studied. Although the uptake of 45Ca into the ER was enhanced by adenosine 5'-triphosphate (ATP) at concentrations lower than 2 mM, at higher concentrations ATP induced 45Ca release from the ER, suggesting that bidirectional translocation of Ca2+ takes place in the ER membrane. When apyrase was added to the reaction mixture to decompose all ATP molecules, the amount of 45Ca in the ER was decreased, indicating that ATP is necessary to retain Ca2+ in the ER. Not only inositol 1,4,5-trisphosphate (IP3) but also guanosine 5'-triphosphate (GTP) was effective in releasing Ca2+ from the ER at concentrations higher than 2 microM, while guanosine 5'-[gamma-thio]-triphosphate (GTP-gamma S), a non-hydrolysable analogue of GTP, was not effective. This may indicate that a hydrolysis of GTP is necessary for Ca2+ release from the ER. Intracellular Ca2+ blockers such as 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) and dantrolene sodium were effective in inhibiting Ca2+ release from ER induced by IP3. The Ca2+ release due to IP3 was also inhibited by flunarizine, a Ca2+ channel blocker, and by oxatomide, an antiallergic drug. Since these two compounds are diphenylpiperazine derivatives, it is suggested that a diphenylpiperazine moiety may be effective in inhibiting Ca2+ release from the ER.

Adenosine Triphosphate↗