Effects of IP3 analogues on Ca2+ release by subtypes of IP3 receptor.

The EC50, pEC50, Hill coefficient (h) and fraction of the intracellular Ca2+ stores released by a maximally effective concentration of each analogue are shown for each IP3R subtype. All results (except EC50) are shown as means ± SEM from n independent experiments. The (1,3,4,5)IP4 was provided by Calbiochem. ND, not determined.aCa2+ release evoked with 100 µM of the analogue (where the highest attainable concentrations of ligand failed to saturate the response).bEC50 estimated by assuming that maximally effective concentrations of (1,3,4,5)IP4 and (1,4,5)IP3 release the same fraction of the Ca2+ stores.*Denotes Hill slopes that are significantly different (P2+ release and pEC50 values used paired comparisons (Δmax or ΔpEC50), which are presented in Table 2.