Effect of Ca2+ influx on intracellular free Ca2+ responses in antigen-stimulated RBL-2H3 cells.
We undertake a quantitative investigation of changes in intracellular free Ca2+ concentration ([Ca2+]i) in antigen-stimulated rat basophilic leukemia (RBL-2H3) cells, which include contributions of both Ca2+ store release and Ca2+ influx from the medium. Following Keizer and De Young (J. Keizer and G. De Young. Biophys. J. 61: 649-660, 1992), we develop a highly constrained mathematical model for [Ca2+]i oscillations in RBL-2H3 cells, which includes activation of the inositol trisphosphate receptor (IP3R) by inositol 1,4,5-trisphospate, indirect Ca2+ activation of the IP3R via Ca2+ -dependent activity of phospholipase C-gamma, slow inhibition of the IP3R by cytosolic Ca2+, refilling of Ca2+ stores by a Ca2+ -ATPase (SERCA)-type pump, and a simple representation of the dependence of plasma membrane (PM) fluxes on experimental conditions. Using this full (open cell) model, we simulate [Ca2+]i responses for protocols in which antigen concentration and external Ca2+ are manipulated and compare out calculations with experimental data. In protocol A, cells are stimulated in the presence of external Ca2+, in protocols B and C, cells are stimulated in the absence of external Ca2+, with external Ca2+ later reapplied in protocol C. We are able to reproduce quantitatively the important features of all three protocols, including the dose response of protocol B, the [Ca2+]i response to thapsigargin, and lag time results, and we provide qualitative explanations for the responses derived from our calculations. We also develop a simplified (closed cell) version of the model in which PM fluxes are neglected and total free Ca2+ concentration ([Ca2+]T) is a slowly varying parameter. This permits us to explain in a simple graphical fashion how PM fluxes may influence [Ca2+]i responses in RBH-2H3 cells through modulation of [Ca2+]T.
Smith
G D
GD
Institute of Theoretical Dynamics, Section of Neurobiology, Physiology, and Behavior, University of California, Davis 95616, USA.
Lee
R J
RJ
Oliver
J M
JM
Keizer
J
J
D000818:Animals; D000941:Antigens / Q000494:pharmacology*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D004140:Dinitrophenols / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D015471:Leukemia, Basophilic, Acute; D008433:Mathematics; D008954:Models, Biological; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D012710:Serum Albumin, Bovine / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
D000941:Antigens; D015220:Calcium Channels; D004140:Dinitrophenols; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; C034638:dinitrophenyl-bovine serum albumin; D012710:Serum Albumin, Bovine; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D000252:Calcium-Transporting ATPases; D002118:Calcium