| Species | Original | Mutated to | Mutation | |
| Human | Glu 557 | |||
| Rat Equivalent | Glu 592 | Arg | ||
| Mouse Equivalent | Glu 591 | |||
This mutation had little effect on the single-channel conductance. When it was combined with R436D, the double mutation produced conductance that was greater than the sum of the individual mutations. When it was combined with R440A, there was no such synergy. In a triple mutation of R432Q, R436D, and R440A, the single-channel conductance increased substantially.
See Equivalent Mutation in R440A