Table I.

Conductance and permeability ratios for various monovalent cations in WT and chimeric M3–M4 loop 5-HT3A receptors

Test cation Radius M3–M4 loopa gX/gNa ±SEM Vr ± SEM VX-VNa PX/PNa n 
 Åb    mV    
Lithium 0.9 + 0.3 0.05 −11.6 ± 2.4 0.6 1.01 4 
 − 0.15 0.03 −4.1 ± 2.9 3.6 1.14 4 
Sodium 1.0 + 1  −12.2 ± 3.0 0 1.00 4 
 − 1  −7.7 ± 2.3 0 1.00 4 
Ammonium 1.7 + 0.4 0.1 −11.4 ± 8.1c 0.8 1.02 4 
 − 0.3 0.1 10.9 ± 2.6c 18.6 2.07 4 
Methylammonium 1.8 + 0.14 0.09 −4.5 ± 1.8 7.7 1.35 5 
 − 0.14 0.04 −8.7 ± 0.8 −1.0 0.95 4 
Ethanolammonium 2.4 + 0.05 0.01 −14.9 ± 0.7 −2.7 0.89 5 
 − −0.01 0.02 −13.3 ± 1.2 −5.6 0.79 4 
2-Methylethanolammonium 2.6 + −0.003 0.05 −28.3 ± 1.0 −16.1 0.52 4 
 − 0.07 0.06 −19.7 ± 1.7 −12.0 0.61 4 
Dimethylammonium 2.6 + −0.02 0.01 −25.7 ± 2.4 −13.5 0.58 3 
 − 0.06 0.01 −24.2 ± 1.3 −16.5 0.51 4 
Diethanolammonium 2.8 + 0.01 0.01 −36.7 ± 1.2 −24.5 0.37 3 
 − 0.04 0.02 −27.2 ± 1.6 −19.5 0.45 4 
Tetramethylammonium 2.9 + 0.01 0.01 −18.0 ± 1.8c −5.8 0.78 4 
 − −0.01 0.01 −46.2 ± 2.3c −38.5 0.21 4 
Choline 3.2 + −0.01 0.01 −46.7 ± 1.5c −34.5 0.25 4 
 − 0.01 0.01 −23.6 ± 2.2c −15.9 0.52 4 
Tris 3.3 + 0.04 0.04 −40.7 ± 1.4 −28.5 0.31 4 
 − 0.06 0.05 −46.4 ± 0.1 −38.7 0.21 4 
NMDG 4.5 + 0.10 0.10 −68.6 ± 1.7 −56.4 0.10 4 
 − 0.15 0.10 −70.7 ± 1.2 −63.0 0.07 4 
Sucrose  +   −63.8 ± 1.8 −51.6 0.12 3 
 −   −69.5 ± 2.3 −61.8 0.08 4 
Test cation Radius M3–M4 loopa gX/gNa ±SEM Vr ± SEM VX-VNa PX/PNa n 
 Åb    mV    
Lithium 0.9 + 0.3 0.05 −11.6 ± 2.4 0.6 1.01 4 
 − 0.15 0.03 −4.1 ± 2.9 3.6 1.14 4 
Sodium 1.0 + 1  −12.2 ± 3.0 0 1.00 4 
 − 1  −7.7 ± 2.3 0 1.00 4 
Ammonium 1.7 + 0.4 0.1 −11.4 ± 8.1c 0.8 1.02 4 
 − 0.3 0.1 10.9 ± 2.6c 18.6 2.07 4 
Methylammonium 1.8 + 0.14 0.09 −4.5 ± 1.8 7.7 1.35 5 
 − 0.14 0.04 −8.7 ± 0.8 −1.0 0.95 4 
Ethanolammonium 2.4 + 0.05 0.01 −14.9 ± 0.7 −2.7 0.89 5 
 − −0.01 0.02 −13.3 ± 1.2 −5.6 0.79 4 
2-Methylethanolammonium 2.6 + −0.003 0.05 −28.3 ± 1.0 −16.1 0.52 4 
 − 0.07 0.06 −19.7 ± 1.7 −12.0 0.61 4 
Dimethylammonium 2.6 + −0.02 0.01 −25.7 ± 2.4 −13.5 0.58 3 
 − 0.06 0.01 −24.2 ± 1.3 −16.5 0.51 4 
Diethanolammonium 2.8 + 0.01 0.01 −36.7 ± 1.2 −24.5 0.37 3 
 − 0.04 0.02 −27.2 ± 1.6 −19.5 0.45 4 
Tetramethylammonium 2.9 + 0.01 0.01 −18.0 ± 1.8c −5.8 0.78 4 
 − −0.01 0.01 −46.2 ± 2.3c −38.5 0.21 4 
Choline 3.2 + −0.01 0.01 −46.7 ± 1.5c −34.5 0.25 4 
 − 0.01 0.01 −23.6 ± 2.2c −15.9 0.52 4 
Tris 3.3 + 0.04 0.04 −40.7 ± 1.4 −28.5 0.31 4 
 − 0.06 0.05 −46.4 ± 0.1 −38.7 0.21 4 
NMDG 4.5 + 0.10 0.10 −68.6 ± 1.7 −56.4 0.10 4 
 − 0.15 0.10 −70.7 ± 1.2 −63.0 0.07 4 
Sucrose  +   −63.8 ± 1.8 −51.6 0.12 3 
 −   −69.5 ± 2.3 −61.8 0.08 4 
a

M3–M4 loop: +, WT loop; −, glvM3M4 loop.

b

Ionic radii from Cohen et al. (1992).

c

A significant difference (P < 0.05) between reversal potential for WT and glvM3M4 loop by one-way ANOVA.

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