Figure 2.

Possible roles for Ca²⁺ channels in B cells. The BCR-induced Ca²⁺ signal involves the production of Ins(1,4,5)P₃ and the release of Ca²⁺ from intracellular stores gated by InsP₃Rs and RyR1. This is followed by an influx of Ca²⁺ through an unidentified store-operated channel (SOC). The mechanism of activation of RyR1 is unknown. Note that RyR1 and InsP₃R are unlikely to be present on the same intracellular stores. The possible involvement of NAADP receptors in BCR signalling is highly speculative. The roles of plasma membrane InsP₃Rs and the l-type Ca²⁺ channel are unknown – the possibility that they may mediate Ca²⁺ influx is indicated by dotted lines. The identification of the l-type Ca²⁺ channel as an NAADP receptor is speculative. CD20 and annexin V are shown as possible Ca²⁺ channels. Intracellular stores are depicted in blue, and activation steps are shown by red arrows.