Ins(1,2,5,6)P4 is one of the many inositol phosphate isomers that act as small, soluble second messengers in the transmission of cellular signals.{8672,8344,13727}. Ins(1,2,5,6)P4 binds to the murine Grp-1 PH domain with a Kd(apparent) of 0.18 μM, which is about 6.7-fold higher than for Ins(1,3,4,5)P4.{13724} It binds to rat heart membranes and significantly decreases heart rate in a pithed rat model.{14740}