Hi Eunus, I have no specific experience with EC cells, but normally for our calcium measuremnts we also use similar TG treatment times. Since cytosolic calcium will still be there, I am not sure whether depleting ER stores should give you a negative effect at all with respect to secretion (Hope you are already aware of this old insulin secretion paper- http://www.sciencedirect.com/science/article/pii/002432059502095Z ). May be as u speculate already, combining TG with EGTA in medium will result in depletion of cytosolic calcium and affect secretion. Good Luck.