Table 2. Relative potencies of IP₃ analogues at different IP₃ receptor subtypes.

	IP3R1			IP3R2			IP3R3
	ΔpEC50	Δmax (%)	(1,4,5)IP3max (%)	ΔpEC50	Δmax (%)	(1,4,5)IP3max (%)	ΔpEC50	Δmax (%)	(1,4,5)IP3max (%)
(4,5)IP2	1.92±0.15	13±5	81±3	1.92±0.05	8±3	65±4	1.38±0.06*	−1±2	77±4
2-deoxy(1,4,5)IP3	0.09±0.10	−1±2	81±3	0.19±0.14	−3±3	63±4	−0.17±0.08	0±2	77±4
(1,4,6)IP3	1.57±0.09	−2±5	76±5	1.67±0.15	−3±6	64±5	1.45±0.09	8±6	55±7
3-deoxy(1,4,5)IP3	1.61±0.12	21±2*	80±4	1.64±0.21	12±4*	68±3	1.66±0.17	20±5*	66±3
(1,3,4,5)IP4 a	2.09±0.07	17±5a	77±1	2.18±0.04	7±0*	67±6	2.38±0.07	NDa	77±4
MG(1,4,5)IP3	0.69±0.10	4±5	77±3	0.7±0.14	11±3*	64±3	0.64±0.15	4±4	61±3

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 (P<0.05) from IP₃R1 (for ΔpEC₅₀ values) or from (1,4,5)IP₃ in paired comparisons with the analogue (for Δmax values).