Figure 5.

Permeation of divalent cations through αS589 mutant channels. (A) Typical traces of amiloride-sensitive whole-cell currents in BAPTA-injected oocytes superfused with 40 mM Ca²⁺ solution (see Methods) and expressing ENaC wt or the αS589D mutant. Currents were elicited by 500-ms voltage steps from a holding potential of −20 mV to test potentials of −160 to +40 mV in 20-mV increments. The dotted line indicates zero level of the amiloride-sensitive current. (B) I/V relationship of ENaC wt (○), the αS589A (■), αS589C (▾), and αS589D (▴) mutant are shown. Conditions were as described in A. For each oocyte, the amiloride-sensitive current was normalized to the I_Na at −100 mV. I_Na at −100 mV was 32.6 ± 14.9 μA for wt, 14.5 ± 1.7 μA for αS589A, 2.9 ± 2.0 μA for αS589C, and 5.6 ± 0.6 μA for the αS589D mutant. Shown are mean ± SEM from at least five oocytes per condition.