Ins(1,2,3,5)P4 is one of the many inositol phosphate isomers that could act as small, soluble second messengers in the transmission of cellular signals.{8672,8344,13727} Ins(1,2,3,5)P4 exhibits relatively weak agonist activity at the Ins(1,4,5)P3 receptor expressed in CHO cells, where it induces Ca2+ mobilization with an ED50 vlau of 93.3 μM, making it nearly 1,000-fold less effective than Ins(1,4,5)P3 in the same assay.{5630}