FIGURE 6.

State-dependent accessibility of extracellular MTSEA in xASIC1.1-M85C. A, representative example of whole-cell currents evoked by pH 6.9 (bar above current traces) before and after exposing closed channels (pH 7.6) to consecutive 5-s treatments with 2.5 mm MTSEA. After MTSEA exposure, cells were washed for 10 s with reagent-free solution pH 7.6. B, similar experiment to A, but the application of MTSEA was at pH 7.3 when channels are desensitized. 10 s at pH 7.6 completely recovers channels from desensitization. C, cumulative effect of MTSEA on peak currents. Each data point is the mean ± S.D. of at least five oocytes. The lines are the fit to a single exponential from which the time constant t was used to calculate the apparent modification rate (R = 100 m⁻¹ s⁻¹) according to Equation 3.