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TABLE I

Pf% for Wild Type, Tagged, and Mutant P2X1, P2X2, P2X3, and P2X4 Receptors


Protein
[ATP] (μM)
pA/pF
Pf%
n
Δ from P2X1?
Δ from P2X2?
Δ from hP2X4?
P2X1 WT P2X1 77 ± 17 12.1 ± 0.8 – Yes Yes 
 P2X1-EE 152 ± 34 11.6 ± 0.6a 11 – Yes Yes 
 (pooled P2X1120 ± 20 11.8 ± 0.5 19 – Yes Yes 
P2X2 WT P2X2 30 314 ± 22b 5.7 ± 0.4c 18 Yes – Yes 
 P2X2-FLAG 302 ± 41 6.7 ± 0.2d 55 Yes – Yes 
Chimerae P2X2-TM1X1 329 ± 66 9.3 ± 0.6 Yes Yes Yes 
 P2X2-TM2X1 103 ± 23 2.6 ± 0.3 Yes Yes Yes 
 P2X2-TM1/2X1 10 39 ± 16 8.9 ± 0.4 Yes Yes Yes 
pH on WT P2X1 (pH 5) 10 111 ± 29 5.8 ± 0.8 Yes No Yes 
 P2X2 (pH 5) 257 ± 30 5.8 ± 0.8 Yes No Yes 
P2X1 mutants P2X1-E52Q 130 ± 20 8.4 ± 0.5 13 Yes No Yes 
 P2X1-E52Q (pH 5) 30 225 ± 65 6.0 ± 0.7e Yes No Yes 
 P2X1-D327S 182 ± 35 10.5 ± 0.5 11 No Yes Yes 
 P2X1-DM 10 82 ± 20 6.1 ± 0.6f 11 Yes No Yes 
 P2X1-DM (pH 5) 30 39 ± 7 5.8 ± 1.6 Yes No Yes 
 P2X1-Y51H 90 ± 28 6.3 ± 0.8 Yes No Yes 
 P2X1-Y51V 85 ± 23 13.2 ± 1.3 No Yes No 
P2X2 mutants P2X2-Q52E 185 ± 57 11.2 ± 0.8 No Yes Yes 
 P2X2-S326D 140 ± 68 11.0 ± 0.9 No Yes Yes 
 P2X2-DM 10 107 ± 15 13.4 ± 0.9 12 No Yes No 
 P2X2-DM (pH 5) 132 ± 25 6.6 ± 1.3g Yes No Yes 
P2X3 P3X3 69 ± 21 4.8 ± 0.3 Yes Yes Yes 
 P2X3-H45Y 132 ± 39 6.7 ± 0.5h Yes No Yes 
P2X4 hP2X4 10 154 ± 53 16.0 ± 1.0 11 Yes Yes – 
 hP2X4-E51Q 10 101 ± 33 14.6 ± 1.1 No Yes No 
 hP2X4-D332S 10 199 ± 60 13.0 ± 0.6 No Yes No 
 hP2X4-DM 30 111 ± 22 8.6 ± 0.6i Yes No Yes 
 zP2X4.1 1000 11 ± 3 7.3 ± 1.3 Yes No Yes 

Protein
[ATP] (μM)
pA/pF
Pf%
n
Δ from P2X1?
Δ from P2X2?
Δ from hP2X4?
P2X1 WT P2X1 77 ± 17 12.1 ± 0.8 – Yes Yes 
 P2X1-EE 152 ± 34 11.6 ± 0.6a 11 – Yes Yes 
 (pooled P2X1120 ± 20 11.8 ± 0.5 19 – Yes Yes 
P2X2 WT P2X2 30 314 ± 22b 5.7 ± 0.4c 18 Yes – Yes 
 P2X2-FLAG 302 ± 41 6.7 ± 0.2d 55 Yes – Yes 
Chimerae P2X2-TM1X1 329 ± 66 9.3 ± 0.6 Yes Yes Yes 
 P2X2-TM2X1 103 ± 23 2.6 ± 0.3 Yes Yes Yes 
 P2X2-TM1/2X1 10 39 ± 16 8.9 ± 0.4 Yes Yes Yes 
pH on WT P2X1 (pH 5) 10 111 ± 29 5.8 ± 0.8 Yes No Yes 
 P2X2 (pH 5) 257 ± 30 5.8 ± 0.8 Yes No Yes 
P2X1 mutants P2X1-E52Q 130 ± 20 8.4 ± 0.5 13 Yes No Yes 
 P2X1-E52Q (pH 5) 30 225 ± 65 6.0 ± 0.7e Yes No Yes 
 P2X1-D327S 182 ± 35 10.5 ± 0.5 11 No Yes Yes 
 P2X1-DM 10 82 ± 20 6.1 ± 0.6f 11 Yes No Yes 
 P2X1-DM (pH 5) 30 39 ± 7 5.8 ± 1.6 Yes No Yes 
 P2X1-Y51H 90 ± 28 6.3 ± 0.8 Yes No Yes 
 P2X1-Y51V 85 ± 23 13.2 ± 1.3 No Yes No 
P2X2 mutants P2X2-Q52E 185 ± 57 11.2 ± 0.8 No Yes Yes 
 P2X2-S326D 140 ± 68 11.0 ± 0.9 No Yes Yes 
 P2X2-DM 10 107 ± 15 13.4 ± 0.9 12 No Yes No 
 P2X2-DM (pH 5) 132 ± 25 6.6 ± 1.3g Yes No Yes 
P2X3 P3X3 69 ± 21 4.8 ± 0.3 Yes Yes Yes 
 P2X3-H45Y 132 ± 39 6.7 ± 0.5h Yes No Yes 
P2X4 hP2X4 10 154 ± 53 16.0 ± 1.0 11 Yes Yes – 
 hP2X4-E51Q 10 101 ± 33 14.6 ± 1.1 No Yes No 
 hP2X4-D332S 10 199 ± 60 13.0 ± 0.6 No Yes No 
 hP2X4-DM 30 111 ± 22 8.6 ± 0.6i Yes No Yes 
 zP2X4.1 1000 11 ± 3 7.3 ± 1.3 Yes No Yes 

P2X1-EE and P2X2-FLAG are the epitope-tagged receptors (P2X1-EYMPME and P2X2-DYKDDDDK, respectively) that served as templates for mutagenesis. The concentrations of agonist ([ATP]) used in the study were chosen to give measurable responses while avoiding dye saturation, and the pA/pFs are the average current densities measured at these concentrations. Wild-type (WT) P2X1 and epitope-tagged P2X1-EE receptors did not differ in Pf%s, and the pooled data were used as control in subsequent statistical evaluations. Although the Pf% of the tagged P2X2-FLAG receptor measured here is the same as that of the WT P2X2 receptor measured in our previous work reported elsewhere (Egan and Khakh, 2004), we did not pool these two datasets because they were obtained in separate studies performed at distinct locations (Cambridge, UK versus St. Louis, MO). Thus, all comparisons in the present study reflect differences from the P2X2-FLAG receptor. In the three rightmost columns, we compare the Pf%s of mutants and chimerae to the parent receptors. Data that are significantly different from P2X1, P2X2, and hP2X4 receptors are marked “Yes” and data that show no difference are marked “No.” All data were obtained at extracellular pH 7.4 except where noted.

a

Not different from the WT P2X1 receptor.

b

Unpublished data (n = 10); Li, personal communication.

c

Data (n = 18) from Egan and Khakh (2004).

d

Not different from the WT P2X2 receptor.

e

Significantly different from P2X2-E52Q (pH 7.4).

f

Significantly different from WT P2X1, P2X1-E52Q, and P2X1-S327S.

g

Significantly different from P2X2-DM (pH 7.4).

h

Significantly different from the WT P2X3.

i

Significantly different from wild-type hP2X4, hP2X4-E51Q, and hP2X4-S332S.

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