Independent regulation of Ca2+ entry and release from internal stores in activated B cells.
Addition of crosslinking antibody to B lymphocytes results in a rapid rise in cytoplasmic-free Ca2+ ([Ca2+]i) due to release of Ca2+ from internal stores and uptake of Ca2+ across the plasma membrane. Inositol 1,4,5-trisphosphate is believed to mediate the release of internal Ca2+ stores and has also been proposed to mediate extracellular Ca2+ entry. We have compared the properties of these two pathways for Ca2+ mobilization by dissociating the [Ca2+]i changes in ligand-activated human B cells after loading of the cells with the Ca2+ chelator BAPTA. In the present paper we show that: (a) the sustained increase in [Ca2+]i is due to increased unidirectional influx of external [Ca2+]i; (b) entry of extracellular Ca2+, but not release of internal stores, is sensitive to the transmembrane potential; and (c) entry of extracellular Ca2+, but not release of internal stores, is inhibited by increasing [Ca2+]i. These findings suggest that the permeation pathways mediating the translocation of Ca2+ across the plasma membrane and endoplasmic reticulum membrane are not identical.
Gelfand
E W
EW
Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
MacDougall
S L
SL
Cheung
R K
RK
Grinstein
S
S
D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004987:Ethers / Q000494:pharmacology; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D015759:Ionomycin; D007700:Kinetics; D008213:Lymphocyte Activation; D014066:Palatine Tonsil / Q000276:immunology
D000888:Antibodies, Anti-Idiotypic; D004987:Ethers; D007075:Immunoglobulin M; D015759:Ionomycin; D002118:Calcium