Quantitative relationships between aggregation of IgE receptors, generation of intracellular signals, and histamine secretion in rat basophilic leukemia (2H3) cells. Enhanced responses with heavy water.
RBL-2H3 cells (a tumor analog of rat mast cells) have plasma-membrane receptors that bind immunoglobulin E, which when aggregated, initiate degranulation. As in other systems, secretion is preceeded by enhanced hydrolysis of inositol phospholipids and by a rise in intracellular Ca2+. Unlike the responses of many other cells, however, both of these earlier events require extracellular Ca2+. The relationship of these events to each other and to the subsequent secretory process is thus unclear. By exposing cells to covalent oligomers of IgE one can demonstrate substantial increases in secretion of histamine by increasing the concentration and size of the oligomers or by using heavy water (D2O) in the medium. We have used such maneuvers to examine the quantitative relationships between aggregation of the receptors and the breakdown of inositol phospholipids, the increase in cytosolic Ca2+ and secretion. Our principal findings were: all treatments that increased secretion, correspondingly increased the changes that precede degranulation. These early events correlated with the degree of aggregation of the receptors even when the stimulatory conditions resulted in maximal secretion. Although the results were insufficient to prove that the hydrolysis of inositol phospholipids is required for the rise in cytosolic Ca2+, the studies with D2O and other observations supported this view. Since a plasma-membrane ion channel for Ca2+ has been implicated in the IgE-mediated rise in cytosolic Ca2+ in RBL 2H3 cells, this in turn suggests a heretofore undescribed role for hydrolysis of inositol phospholipids.
Maeyama
K
K
Hohman
R J
RJ
Metzger
H
H
Beaven
M A
MA
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D003903:Deuterium / Q000378:metabolism*; D017666:Deuterium Oxide; D006636:Histamine Release; D006868:Hydrolysis; D007073:Immunoglobulin E / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D007938:Leukemia / Q000378:metabolism*; D046911:Macromolecular Substances; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D011961:Receptors, Fc / Q000378:metabolism*; D017455:Receptors, IgE; D011971:Receptors, Immunologic / Q000378:metabolism*; D013997:Time Factors; D014867:Water / Q000378:metabolism*
D007295:Inositol Phosphates; D046911:Macromolecular Substances; D010716:Phosphatidylinositols; D011961:Receptors, Fc; D017455:Receptors, IgE; D011971:Receptors, Immunologic; D014867:Water; D007073:Immunoglobulin E; D003903:Deuterium; D017666:Deuterium Oxide; D002118:Calcium