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Table 3.

Phenotype of the P2X_2-3/3 receptor expressed in Xenopus oocytes compared with the spiral ganglion neuron P2X receptor and other recombinant P2X receptor isoforms

	P2X_2-3/3^*	SGN^†	P2X_2-1/3^‡	P2X_2-1^§¶,**	P2X_2-3^††	P2X₃^¶,‡‡
α,βmeATP	+	+	+	−	−	+
2meSATP	+	+	−	+	+	+
ADP	+	+	−	−	−	+
Desensitization	Fast	Fast	Slow	Slow	Slow	Very fast
	(5 seconds)	(2 seconds)				(100 mseconds)
ATP (EC₅₀)	0.45 μM	18 μM	1 μM	1-62 μM^§§	9 μM	1 μM
Protons	Potentiate	Potentiate	Potentiate	Potentiate	Potentiate	Inhibit
TNP-ATP (IC₅₀)	3.5 μM	407 nM	4 nM	1 μM	nd	1 nM

	P2X_2-3/3^*	SGN^†	P2X_2-1/3^‡	P2X_2-1^§¶,**	P2X_2-3^††	P2X₃^¶,‡‡
α,βmeATP	+	+	+	−	−	+
2meSATP	+	+	−	+	+	+
ADP	+	+	−	−	−	+
Desensitization	Fast	Fast	Slow	Slow	Slow	Very fast
	(5 seconds)	(2 seconds)				(100 mseconds)
ATP (EC₅₀)	0.45 μM	18 μM	1 μM	1-62 μM^§§	9 μM	1 μM
Protons	Potentiate	Potentiate	Potentiate	Potentiate	Potentiate	Inhibit
TNP-ATP (IC₅₀)	3.5 μM	407 nM	4 nM	1 μM	nd	1 nM

^*This study; ^†Salih et al.,2002; ^‡Lewis et al., 1995; ^§Brake et al.,1994, King et al.,1996, Khakh et al.,2001; ^¶North,2002; ^**Kanjhan et al., 2003; ^‡D.G. et al., unpublished; ^‡‡Chen et al.,1995; ^§§EC50 reported for ATP at P2X2 receptors is variable (see §,¶,^**). +, response; −,no response; nd, not determined.

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