Increased plasma membrane permeability to Ca2+ in anti-Ig-stimulated B lymphocytes is dependent on activation of phosphoinositide hydrolysis.
The biochemical basis of Ca2+ mobilization after anti-Ig binding to B cell Ag-R has been further characterized by flow cytometric analysis of indo-1-loaded B cells. The ability to distinguish intracellular Ca2+ release from extracellular Ca2+ influx by using an extracellular calcium depletion-repletion approach has allowed us to study the relationship between the mobilization of Ca2+ from these sources. Studies involving manipulation of the Ca2+ gradient across the plasma membrane indicate that a significant portion of the Ca2+ mobilization response is preserved even when the normal inwardly directed Ca2+ gradient is reversed. In the presence of an extracellular calcium concentration ([Ca2+]o) of 10 microM, the response to anti-Ig is not blocked by the organic Ca2+ channel blockers. This response is not reduced by further depletion of [Ca2+]o by EGTA Ca2+-binding buffers. Thus, the Ca2+ response that occurs when [Ca2+]o less than or equal to 10 microM represents intracellular calcium release. Analysis of B cells stimulated with anti-Ig in low Ca2+ medium ([Ca2+]o = less than 10 microM) followed by repletion of [Ca2+]o to 1 to 5 mM reveals that a significant increase in permeability of the plasma membrane to Ca2+ develops in the stimulated cells. The resultant Ca2+ influx is nimodipine (20 microM) sensitive. Both intracellular Ca2+ release and Ca2+ influx are reduced in parallel as the concentration of anti-Ig stimulus is decreased, suggesting that Ca2+ influx may be coupled to the release of intracellular stores. Neomycin blocks anti-Ig-stimulated formation of inositol trisphosphate, which mediates release of Ca2+ from the endoplasmic reticulum. It also blocks the anti-Ig-induced release of intracellular Ca2+ stores as well as Ca2+ influx, indicating that both responses may be dependent upon phosphatidylinositol 4,5-bisphosphate hydrolysis.
Ransom
J T
JT
Department of Medicine, National Jewish Center for Immunology and Respiratory Medicine, Denver, CO 80206.
Chen
M
M
Sandoval
V M
VM
Pasternak
J A
JA
Digiusto
D
D
Cambier
J C
JC
D000818:Animals; D000888:Antibodies, Anti-Idiotypic; D000937:Antigen-Antibody Reactions; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002451:Cell Compartmentation; D002463:Cell Membrane Permeability; D007145:Immunoglobulin kappa-Chains; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism*; D051379:Mice; D009355:Neomycin / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000502:physiology*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D013403:Sugar Phosphates / Q000378:metabolism*
D000888:Antibodies, Anti-Idiotypic; D007145:Immunoglobulin kappa-Chains; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011947:Receptors, Antigen, B-Cell; D013403:Sugar Phosphates; D009553:Nimodipine; D009355:Neomycin; D002118:Calcium