Fig. 4. Deletion of PERK does not affect IP₃ production, localization of IP₃Rs and IP₃-mediated Ca²⁺ release in pancreatic acinar cells. (A,B) WT (filled symbols and columns) and PERK^-/- pancreatic acini (open symbols and columns) were stimulated with the indicated concentrations of carbachol (A), bombesin (BS) or CCK (B) for 2-10 seconds and the mass of 1,4,5 IP₃ was measured. (C) Pancreatic acini were fixed and used for immunolocalization of IP₃R1 (upper images), IP₃R2 (middle images) or IP₃R3 (bottom images) in WT and PERK^-/- cells. (D) Pancreatic acini from WT and PERK^-/- mice were permeabilized with streptolysin O and after stabilization of medium Ca²⁺ at about 55 nM, increasing concentrations of IP₃ were added to the incubation medium to measure the ability of IP₃ to release Ca²⁺ from the ER ( indicates addition of 0.15 µM IP₃; arrow indicates addition of 5 µM IP₃). The results of three experiments are summarized in E and are given as the mean ± s.e.m.