Figure 2. The K+/Na+ permeability ratio is increased by αS589 mutations. Current-voltage relationship in 120-mM Na+ and 120-mM K+ bath solution from oocytes expressing αS589A, αS589C, and αS589N measured with two-electrode voltage clamp. Currents were measured during 1-s voltage steps from a holding potential of −20 mV to test potentials of −140 to +40 mV in 20-mV increments. Currents measured in the presence of 10 μM amiloride were subtracted from currents measured in the absence of amiloride. In each experiment, the amiloride-sensitive Na+ and K+ currents were normalized to the amiloride-sensitive Na+ current at −100 mV. To allow Na+ to enter the oocyte during the expression phase without downregulation of channel activity, mutant α subunits were coexpressed with β subunits containing the Liddle mutation βY618A together with wt γ ENaC and oocytes were kept in a solution containing 90 mM Na+ during the expression phase (Kellenberger et al. 1998). The mutation βY618A does not affect ion selectivity. Erev, Na − Erev, K was 114 mV (wt), 96 mV (αS589A), 37 mV (αS589C), and 15 mV (αS589N), n = 4–5. INa at −100 mV was 30.0 ± 3.6 μA (αS589A), 8.3 ± 1.7 μA (αS589C), and 9.3 ± 2.1 μA (αS589N).
Image published in: Kellenberger S et al. (2001)
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