Table 1

Known Ca²⁺ permeabilities of P2X receptors in relation to some other transmitter-gated cation channels

Receptor	p Ca²⁺/ p Na⁺	Fractional Ca²⁺ Current	Reference
		%
P2X₁	∼5		Valera et al., 1994; Evans et al., 1996
P2X₂	2.7	6.5	Rogers and Dani, 1995; Evans et al., 1996
P2X₃	1.2–4		Lewis et al., 1995; Virginio et al., 1998a
P2X₄	4.2	8.2	Buell et al., 1961; Soto et al., 1996b; Garcia-Guzman et al., 1997
P2X_2/3	1.3		Virginio et al., 1998a
P2X_1/5	1.1		Surprenant et al., 2000
NMDA	10.4	8–12	Burnashev, 1998
AMPA	0.09	1–4
α₇-Nicotinic	6.6–20		Seguela et al., 1993; Fucile et al., 2000
5HT_3A ^1-a	1.08		Davies et al., 1999
5HT_3A/B ^1-a	0.62

AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid; NMDA, N -methyl-d-aspartate.
↵1-a The value given is p Ca²⁺/ p Cs⁺, and p Na⁺/ p Cs⁺ is 0.8 for 5HT_3A, and 0.83 for 5HT_3A/B.