Relative potencies of IP3 analogues at different IP3 receptor subtypes.

From paired comparisons with (1,4,5)IP3, the relative potency and differences in maximal Ca2+ release are shown for each analogue at each IP3R subtype. Results show means ± SEM, with n provided in Table 1. To allow direct comparison with responses evoked by (1,4,5)IP3, maximal Ca2+ release evoked by (1,4,5)IP3 in experiments paired with the analogues are also shown ((1,4,5)IP3 max).aWith (1,3,4,5)IP4 it was impossible to attain concentrations (>100 µM) that evoked a maximal response for all IP3R subtypes; in these cases the maximal responses were not subject to statistical analysis. The relative potency of (1,3,4,5)IP4 at IP3R subtypes was estimated by assuming it was a full agonist that released the same fraction of the intracellular Ca2+ stores as a maximally effective concentration of (1,4,5)IP3 in parallel analyses. ND, not determined.*Denotes values significantly different (P3R1 (for ΔpEC50 values) or from (1,4,5)IP3 in paired comparisons with the analogue (for Δmax values).