Figure 5.

Interaction between IP₃R3 and EB3 Is Required for Effective IP₃R3 Clustering

(A) Time-lapse images (times, in s, shown in panels) of GFP fluorescence in HLMVECs expressing GFP-IP₃R3(WT) or GFP-IP₃R3(T804A) after stimulation with α-thrombin (50 nM, at t = 0). Scale bar, 10 μm.

(B and C) Summary results (mean ± SEM from five to seven cells) show the number of clusters for GFP-IP₃R3 and GFP-IP₃R3(T804A) (B) and cluster lifetime (C) after stimulation with α-thrombin (50 nM at t = 0). Data were analyzed using processed images as in Figures 3D and 3E. ^∗∗Using Student’s t test.

(D) Model for EB3-dependent IP₃R3 clustering and amplification of Ca²⁺ signals. EB3 facilitates clustering of IP₃Rs within ER membranes (left). α-Thrombin, via PAR-1, activates PLC and synthesis of IP₃. We propose that IP₃Rs more effectively release Ca²⁺ in response to this IP₃ when they have clustered, possibly because amplification of the signals by Ca²⁺-induced Ca²⁺ release is more effective.