Table 1.

Closed channel conductance and selectivity of HG mutants

MutantgH,closedgH(C/O) pH 7ΔVrev pH 7→6ΔVrev pH 7→8ΔVrev pH 6→5ΔVrev TMA+→Na+
I105GNo056.7 ± 1.6 (6)53.7 ± 3.5 (5)
I105DNo049.4 ± 2.3 (5)49 (1)60 (1)1.8 ± 0.8 (3)
L108TNo053 (1)55.5 ± 3.5 (2)−2.4 (1)
V109TNo052.8 ± 1.1 (4)55.7 ± 1.9 (3)1.6 (1)
V109ANo056.5 ± 1.0 (4)54.0 ± 6.0 (2)1.1 ± 1.3 (3)
L147TNo051.3 ± 3.0 (3)
L147DNo050.7 ± 1.7 (3)53 (1)0.2 ± 0.4 (5)
F150ANo047.5 ± 1.5 (2)52 (1)−0.5 ± 0.8 (4)
V178TNo049 (1)
F182ANo055.8 ± 1.1 (4)50.1 ± 3.0 (2)45−0.9 ± 1.1 (3)
V177TNo047.0 ± 4.0 (3)53.8 ± 2.5 (5)−0.3 ± 1.0 (3)
V177DYes0.103 ± 0.014 (8)55.3 ± 3.7 (3)0.5 ± 0.2 (3)
V178AYes0.017 ± 0.010 (5)50.2 ± 1.4 (4)47 (1)0.6 ± 0.7 (3)
V109A/F150AYes0.164 ± 0.044 (6)49.7 ± 3.8 (3)34 (1)0.8 ± 1.1 (4)
V109A/V178AYes0.028 ± 0.012 (7)49.9 ± 1.3 (4)0.8 ± 0.8 (3)
F150A/V178AYes0.144 ± 0.015 (3)44.5 ± 0.5 (2)70 (1)−0.6 ± 0.6 (3)
V178DYes0.036 ± 0.019 (4)57.3 ± 1.4 (4)50.7 ± 2.7 (3)55 (1)0.6 ± 1.2 (6)
V109A/F150A/V178AYes0.35 ± 0.05 (9)44.0 ± 2.8 (5)36.3 ± 4.9 (3)29.7 ± 11.9 (3)−0.3 ± 0.4 (4)
V109DYes0.40 ± 0.06 (5)59 (1)3.0 ± 0.9 (3)
F150DYes0.38 ± 0.09 (4)39.3 ± 3.5 (3)45 (1)39 ± 6 (2)1.2 ± 1.4 (4)
F150D/R211GYes0.67 ± 0.04 (6)39.6 ± 8.2 (5)33.3 ± 8.4 (4)41.0 ± 6.4 (4)1.8 ± 0.4 (5)
  • The existence of gH,closed was defined as consistent reversible changes in the holding current of >1 pA when pH was changed or with addition of Zn2+ or both. Absolute values of Vrev changes with pH are given for both whole-cell and inside-out patch measurements. Mutants with large gH,closed tend to have smaller and more variable Vrev changes with pH because proton leak at Vhold continually dissipates the pH gradient even if the channel is perfectly proton selective, to an extent dependent on geometry and other factors. Parameter gH(C/O) is the ratio of closed to open gH (Materials and Methods). Monovalent cation substitutions were done at pH 7//7, and measured liquid junction potentials have been corrected.