Slow and persistent increase of [Ca2+]c in response to ligation of surface IgM in WEHI-231 cells

Abstract

WEHI-231 and Bal 17 B cell lines are representative models for immature and mature B cells, respectively. Their regulation of cytosolic Ca2+ concentration ([Ca2+]c) was compared using fura-2 fluorescence ratiometry. The ligation of B cell antigen receptor (BCR) by anti-IgM antibody induced a slow but large increase of [Ca2+]c in WEHI-231 cells while not in Bal 17 cells. The thapsigargin-induced store-operated Ca2+ entry (SOCE) of Bal 17 cells reached a steady state which was blocked by 2-aminoethoxydiphenyl borate (2-APB). On the contrary, the thapsigargin-induced SOCE of WEHI-231 cells increased continuously, which was accelerated by 2-APB. The increase of [Ca2+]c by BCR ligation was also enhanced by 2-APB in WEHI-231 cells while blocked in Bal 17 cells. The Mn2+ quenching study showed that the thapsigargin-, or the BCR ligation-induced Ca2+ influx pathway of WEHI-231 was hardly permeable to Mn2+. The intractable increase of [Ca2+]c may explain the mechanism of BCR-driven apoptosis of WEHI-231 cells, a well-known model of clonal deletion of autoreactive immature B cells.