Independent movement of the voltage sensors in K2.1/K6.4 heterotetramers.

Heterotetramer voltage-gated K (K) channels K2.1/K6.4 display a gating charge-voltage (Q) distribution composed by two separate components. We use state dependent chemical accessibility to cysteines substituted in either K2.1 or K6.4 to assess the voltage sensor movements of each subunit. By comparing the voltage dependences of chemical modification and gating charge displacement, here we show that each gating charge component corresponds to a specific subunit forming the heterotetramer. The voltage sensors from K6.4 subunits move at more negative potentials than the voltage sensors belonging to K2.1 subunits. These results indicate that the voltage sensors from the tetrameric channels move independently. In addition, our data shows that 75% of the total charge is attributed to K2.1, while 25% to K6.4. Thus, the most parsimonious model for K2.1/K6.4 channels' stoichiometry is 3:1.