Table 1.

P2X receptors showing their molecular, pharmacologic, and functional properties [Adapted from Illes et al. (2021)].

	P2X1	P2X2	P2X3	P2X4	P2X5	P2X6	P2X7
ATP EC50 (μM)	0.56–0.7	2–8	0.5–1	1–10	0.44–10	12	100
Desensitization	Rapid (<1 s)	Slow (>20s) or no desensitization	Rapid (<1 s)	Slow (>20s)	Slow (>20s)	Slow (>20s)	Slow (>20s)
Function	Non-selective cationic channel	Non-selective cationic channel	Non-selective cationic channel	Non-selective cationic channel Permeability for Ca2+ among highest in P2X family	Non-selective cationic channel Permeable to chloride ions	Non-selective cationic channel	Non-selective cationic channel
Large Pore	No	Yes	No	Yes	-	-	Yes
Functional Heterotrimers	P2X2, P2X4, P2X5	P2X1, P2X3, P2X5, P2X6	P2X2	P2X1, P2X6	P2X1, P2X2	P2X2, P2X4	P2X4
Location/ Cellular Expression Within the Retina	Inner plexiform layer, Muller cells, endothelial cells, glial cells	Amacrine cells, Muller cells, neurons	Amacrine cells, neurons	Glial cells, endothelial cells, neurons, horizontal cells of retina, amacrine and ganglion cells of the retina, Muller cells	Amacrine cells	Nerve fiber layer	Plexiform layers, horizontal cells, photoreceptors, amacrine cells, ganglion cells, glial cells, RPE, choroid, Muller cells