Table 7

Ionic permeabilities relative to monovalent ions for glutamate receptors of known subunit composition

Receptor	P_Ca/P_{Na,Cs, K}^7-a	P_C1/P_Na^7-a	P_{f (Ca)}^7-b
GluR1	2.34		0.032	Burnashev et al., 1995
GluR2		0.14		Burnashev et al., 1996
GluR1/GluR2	0.05	∼0	0.005	Burnashev et al., 1995,1996
GluR4			0.039	Burnashev et al., 1995
GluR6(R)^7-c	0.12^7-d	0.74	0.002^7-e	Burnashev et al., 1995, 1996
GluR6(Q)	0.21–1.2	∼0	0.016^7-e	Egebjerg and Heinemann, 1993; Burnashev et al., 1995, 1996
GluR6(R)/GluR6(Q)		∼0	0.006^7-f	Burnashev et al., 1995, 1996
NR1-1a/NR2A	3.10–11	0.1–0.19		Burnashev et al., 1995; Wollmuth et al., 1996; Sharma and Stevens, 1996b;Schneggenburger, 1996, 1998
NR1-1a/NR2B	17		0.175	Iino et al., 1997; Schneggenburger, 1996
NR1-1a/NR2C	2.23		0.082	Burnashev et al., 1995

Na⁺ and Cs⁺ are considered equally permeable.
↵7-a Lewis equation derived from the Goldman-Hodgkin-Katz equation.
↵7-b Proportion of whole-cell current carried by Ca²⁺determined from simultaneous measurement of whole-cell current and Ca²⁺ fluorescence.
↵7-c Results are shown only for studies which either directly measure Ca²⁺ flux or take into consideration the C1⁻permeability.
↵7-d Not significantly different from zero.
↵7-e Editing of transmembrane region 1 had no effect fractional Ca²⁺ current through GluR6(R), but slightly decreases fractional Ca²⁺ current through GluR6(Q).
↵7-f Expressed at a ratio of 1∶1.