Combining the charged V220 mutants with the R217Q mutation. The optical traces of the charged V220 mutants in the presence of the R217 wildtype sequence (same as in
shown here for ease of comparison) are on the left. On the right are the same charged mutants in the presence of the R217Q mutation. Only the negatively charged V220 mutants show an increase in the optical signal during the hyperpolarizing voltage step.