Interaction between Ca2+ and the Channel's Pore in the AChR and NMDAR
| Construct | γNa+−Mg2+ (pS)a | γCa2+ (pS)b | KdCa2+ (mM; activity)c | Kd′Ca2+ (mM; concentration)d | Physiological Ca2+ conductance (pS)e | Physiological fractional Ca2+ current (%)f |
| wild-type/γ AChR (fetal, mouse) | 46 ± 0.1 | 24 ± 0.1 | 1.16 ± 0.04 | 4.0 | 7.5 ± 0.2 | 19.3 ± 0.5 |
| wild-type/ɛ AChR (adult, mouse) | 66 ± 0.1 | 36 ± 0.2 | 1.53 ± 0.05 | 5.3 | 9.4 ± 0.2 | 16.3 ± 0.5 |
| wild-type/ɛ AChR (adult, human) | 73 ± 0.1 | 31 ± 0.2 | 2.22 ± 0.05 | 7.9 | 6.1 ± 0.1 | 9.3 ± 0.2 |
| αS269I (adult, mouse) | 67 ± 0.2 | 35 ± 0.3 | 1.68 ± 0.06 | 5.9 | 8.4 ± 0.2 | 14.3 ± 0.4 |
| βV266M (adult, mouse) | 62 ± 0.2 | 32 ± 0.4 | 2.88 ± 0.13 | 10 | 5.0 ± 0.2 | 8.8 ± 0.4 |
| ɛL221F (adult, mouse) | 68 ± 0.1 | 34 ± 0.2 | 1.54 ± 0.03 | 5.4 | 8.8 ± 0.1 | 15.0 ± 0.3 |
| ɛT264P (adult, mouse) | 74 ± 0.2 | 31 ± 0.2 | 1.29 ± 0.03 | 4.5 | 9.1 ± 0.1 | 15.0 ± 0.3 |
| ɛL269F (adult, mouse) | 61 ± 0.2 | 32 ± 0.2 | 1.92 ± 0.07 | 6.8 | 7.0 ± 0.2 | 13.0 ± 0.4 |
| wild-type NR1-NR2A (rat) | 84 ± 0.2 | 22 ± 0.3 | 0.96 ± 0.02 | 3.3 | 7.9 ± 0.1 | 12.8 ± 0.3 |
| Construct | γNa+−Mg2+ (pS)a | γCa2+ (pS)b | KdCa2+ (mM; activity)c | Kd′Ca2+ (mM; concentration)d | Physiological Ca2+ conductance (pS)e | Physiological fractional Ca2+ current (%)f |
| wild-type/γ AChR (fetal, mouse) | 46 ± 0.1 | 24 ± 0.1 | 1.16 ± 0.04 | 4.0 | 7.5 ± 0.2 | 19.3 ± 0.5 |
| wild-type/ɛ AChR (adult, mouse) | 66 ± 0.1 | 36 ± 0.2 | 1.53 ± 0.05 | 5.3 | 9.4 ± 0.2 | 16.3 ± 0.5 |
| wild-type/ɛ AChR (adult, human) | 73 ± 0.1 | 31 ± 0.2 | 2.22 ± 0.05 | 7.9 | 6.1 ± 0.1 | 9.3 ± 0.2 |
| αS269I (adult, mouse) | 67 ± 0.2 | 35 ± 0.3 | 1.68 ± 0.06 | 5.9 | 8.4 ± 0.2 | 14.3 ± 0.4 |
| βV266M (adult, mouse) | 62 ± 0.2 | 32 ± 0.4 | 2.88 ± 0.13 | 10 | 5.0 ± 0.2 | 8.8 ± 0.4 |
| ɛL221F (adult, mouse) | 68 ± 0.1 | 34 ± 0.2 | 1.54 ± 0.03 | 5.4 | 8.8 ± 0.1 | 15.0 ± 0.3 |
| ɛT264P (adult, mouse) | 74 ± 0.2 | 31 ± 0.2 | 1.29 ± 0.03 | 4.5 | 9.1 ± 0.1 | 15.0 ± 0.3 |
| ɛL269F (adult, mouse) | 61 ± 0.2 | 32 ± 0.2 | 1.92 ± 0.07 | 6.8 | 7.0 ± 0.2 | 13.0 ± 0.4 |
| wild-type NR1-NR2A (rat) | 84 ± 0.2 | 22 ± 0.3 | 0.96 ± 0.02 | 3.3 | 7.9 ± 0.1 | 12.8 ± 0.3 |
Single-channel conductance in a nominally Ca2+-free extracellular solution containing the following (in mM): 150 NaCl, 1.7 MgCl2, and 10 HEPES/KOH, pH 7.4. MgCl2 was omitted in the case of the recordings from rat NR1-NR2A NMDARs (see Results). This parameter, as well as γCa2+ and KdCa2+ were estimated from the fit of the data in Fig. 11 with Eqs. 2–4.
Single-channel conductance in the presence of saturating extracellular Ca2+.
Apparent dissociation equilibrium constant of Ca2+ from the (phenomenologically defined) cation-binding site in the channel's pore in the presence of 150 mM extracellular Na+ and, in the case of the wild-type and mutant AChRs, 1.7 mM extracellular Mg2+. The values are expressed in terms of activity.
Apparent dissociation equilibrium constant of Ca2+ expressed in terms of concentration.
Single-channel conductance of the Ca2+-carried component of the total currents in the presence of [Ca2+]o = 1.8 mM, calculated by dividing Eq. 4 by voltage. Errors were calculated by propagating the errors of the appropriate variables in Eq. 4, assuming that these are independent of each other, and that they are normally distributed.
Fractional contribution of the Ca2+ current to the total current in the presence of [Ca2+]o = 1.8 mM, calculated using Eq. 5. Errors were calculated by propagating the errors of the appropriate variables in this equation, assuming that these are independent of each other, and that they are normally distributed.