TABLE 18.

Pore properties of AMPA, kainate, and NMDA receptors

The relative permeability of Ca²⁺ to monovalent ions (P_Ca/P_X) and the fractional Ca²⁺ current (P_f) values shown are not necessarily those given in the original manuscript but rather have been standardized to common parameters for direct comparison. The values shown are not corrected for activities. Pore dimensions are derived from the permeability of differently sized organic cations. Only values derived from recombinant channels are shown; see Dingledine et al. (1999) for more details and examples of native channels. P_Ca/P_X values are derived from the Lewis equation (see Jatzke et al., 2002) based on changes in reversal potentials given in articles typically measured under bionic conditions where a reference solution (X, usually Cs⁺ or Na⁺) is replaced with a solution containing high Ca²⁺ (typically ≈100 mM). P_Ca/P_X (from P_f) is derived from P_f measurements using the GHK equation (Burnashev et al., 1995). Fractional Ca²⁺ currents (P_f) are the percentage of the total current carried by Ca²⁺ and are measured using whole-cell currents and high concentrations of fura-2 to ensure that all incoming Ca²⁺ is captured by dye. P_f values are concentration- and voltage-dependent with the magnitude of these effects dependent on specific subtypes (Burnashev et al., 1995; Jatzke et al., 2002). The values shown were either recorded at −60 mV and 1.8 mM Ca²⁺ or adjusted to these conditions assuming GHK (see Jatzke et al., 2002).

Subunit Combination	Pore Diameter	PCa/PX	PCa/PX (from Pf)	Pf	PCl/PCs
	nm			%
GluA1a,b	0.78c	1.6	≈0.7	3.2–3.6
GluA2 (Arg)c					0.14
GluA1/GluA2 (Arg)c	0.7	0.03	0.11	0.54	≈0
GluA4				3.9
GluK2 (Gln)a,b,d	0.75g	0.14–0.17	0.30–0.48	1.55–2.4	≈0
GluK2 (Arg)a,c,d	0.76		<0.04	<0.2	0.74
GluK2 (Gln)/GluK2 (Arg)a,c,d	0.74			0.58	≈0
GluN1-GluN2Aa,b,e,f,g	0.55h,i	2.8–4.5	3.0–3.6	11.0–15.9
GluN1-GluN2Bf		3.6	3.6	15.9
GluN1-GluN2Ca		1.8	1.73	8.2
GluN1-GluN3Aj		0.6
GluD2Lc				2.6k,l

^a Burnashev et al. (1995).

^b Jatzke et al. (2002).

^c Burnashev et al. (1996).

^d The kainate receptor GluK2 is edited in three different locations: two in M1 (Ile, Tyr fully unedited and Val, Cys fully edited) and one in M2 (Gln in unedited, Arg in edited). All values shown are for receptors that are fully edited in M1.

^e Sharma and Stevens (1996).

^f Schneggenburger (1996).

^g Schneggenburger (1998).

^h Villarroel et al. (1995).

ⁱ Wollmuth et al. (1996).

^j Perez-Otano et al. (2001).

^k GluD2^Lc is a constitutively active form (Lurcher) of the GluD2 subunit.

^l Wollmuth et al. (2000).