Cross-linking of Surface Immunoglobulin on B Lymphocytes Induces Both Intracellular Ca2+ Release and Ca2+ Influx: Analysis with Indo-1

The new Ca2+-probe indo-1 has a high fluorescence intensity, which allows low intracellular dye loadings. Stimulation of indo-1-loaded mouse B cells with anti-Ig antibodies provoked rapid rise of free cytoplasmic Ca2+ from 100 nM to greater than 1 microM, followed by a decline to a plateau at 300-400 nM. The initial rapid rise was not detected in quin2-loaded cells, presumably due to the Ca2+-buffering effects of the dye. The sustained Ca2+ increase was due to influx, whereas the initial rise was caused by release from intracellular stores. The magnitudes of Ca2+ release and inositol trisphosphate release were closely correlated. Concanavalin A does not provoke inositol trisphosphate release in mouse B cells. It did not induce a rapid initial Ca2+ rise in indo-1-loaded B cells either, but only a sustained increase to 200-300 nM. Finally, Ca2+ influx induced by both anti-Ig and concanavalin A were not affected by membrane depolarization.