TABLE 1.

Measured and adjusted Pf% values

Pf% was measured from HEK293 cells expressing the specific P2X7R listed in the leftmost column. Concentrations are mm. Species are homomeric “a” splice variants unless otherwise noted in parentheses. 0.1 mm BzATP was dissolved in an extracellular solution containing 2 mm CaCl₂ and 1 mm MgCl₂. 0.6 mm BzATP was dissolved in an extracellular solution containing 2 mm CaCl₂ and no added MgCl₂. The estimated concentrations of free Ca²⁺ and Mg²⁺ were calculated using MaxChelator. Pf%_adj is the fractional Ca²⁺ current expected if Pf% could be measured in the absence of Ca²⁺ chelation by the purinergic agonist. P_Ca/P_Na was calculated from the empirically measured Pf% values as described under “Experimental Procedures.”

Species	[BzATP]	[Ca2+]free	[Mg2+]free	Pf%	Pf%adj	PCa/PNa	n
Dog	0.1	1.95	0.95	7.3 ± 0.2	7.5 ± 0.2	1.8 ± 0.0	11
Rat	0.1	1.95	0.95	7.1 ± 0.2	7.3 ± 0.2	1.7 ± 0.1	136
Rat (k)	0.1	1.95	0.95	2.8 ± 0.3a	2.8 ± 0.3a	0.7 ± 0.1a	34
Mouse	0.1	1.95	0.95	7.1 ± 0.4	7.3 ± 0.4	1.7 ± 0.1	11
Mouse (k)	0.1	1.95	0.95	4.3 ± 0.3b	4.4 ± 0.3b	1.0 ± 0.1b	13
Guinea pig	0.6	1.40	0	5.7 ± 0.8	8.2 ± 1.1	1.9 ± 0.3	7
Monkey	0.6	1.40	0	8.0 ± 0.4	11.4 ± 1.0	2.7 ± 0.3	8
Human	0.6	1.40	0	7.1 ± 0.4	10.2 ± 0.6	2.4 ± 0.2	22
Human X7 (a/b)	0.6	1.40	0	8.2 ± 0.3	11.7 ± 0.4	2.9 ± 0.1	8
Zebrafish	0.6	1.40	0	14.3 ± 1.0c	20.4 ± 1.4c	5.6 ± 0.5c	14

^a Significantly different from rP2X7aR.

^b Significantly different from mP2X7aR.

^c Significantly different from all other species.