Figure 2.

Expression of IP₃ receptors in the plasma membrane of DT40 cells. (A) Thapsigargin (top) stimulates Ca²⁺ release (palest line, in Ca²⁺-free medium) and Ca²⁺ entry (black line, in Ca²⁺-containing medium). The latter, SOCE, is entirely blocked by 300 nM GdCl₃ (gray line). The bottom panel shows that activation of the BCR with anti-IgM stimulates both Ca²⁺ release and Ca²⁺ entry, but the latter is only partially inhibited by GdCl₃. (B) Whole-cell patch-clamp recoding from DT40 cells with IP₃, IP₃ with heparin, or adenophostin A in the patch pipette. The holding potential was −100 mV; arrowheads denote the closed state. (C) Current−voltage (i−V) relationships for the IP₃-stimulated currents recorded from the PM or nuclear envelope of DT40-KO cells stably transfected with wild-type IP₃R1 (R1) or IP₃R1 with mutants in the putative pore (G2547A, R1^GA; V2548I, R1^VI). The point mutations similarly affected γ_K of the IP₃-activated currents in both settings. (D) The six TMDs of a single IP₃R subunit are shown to highlight the putative selectivity filter (sf) and the engineered αBgtx-binding site. In whole-cell patch-clamp recordings from DT40 cells expressing IP₃R1 with this αBgtx-binding site, intracellular IP₃ stimulated channel openings, and both P_o and γ_K were increased by extracellular αBgtx. Reproduced from ref (65) with permission. Copyright 2006. American Academy for the Advancement of Science.