Figure 1.

Low internal K⁺ reveals two components of external TEA block. Fraction of Shaker K⁺ channel current blocked by external TEA in 50 mM (A) and 5 mM (B) internal K⁺ at −10 mV (top) and +70 mV (bottom). Data points are the mean values from 3 to 6 measurements with standard error limits for those whose errors are larger than the symbol size. Insets show raw currents in the absence (Control) and presence of 50 mM external TEA. Calibrations: (A) −10 mV, 50 pA/10 ms; +70 mV, 0.2 nA/10 ms; (B) −10 mV, 50 pA/10 ms; +70 mV, 0.1 nA/10 ms. Dashed lines are fits of Eq. 1 to the data with K _app values of (A) −10 mV, 20 mM; +70 mV, 43 mM; (B) −10 mV, 32 mM; +70 mV, 89 mM. Solid lines are fits of Eq. 2 to the data with the A, K _app ^low, and K _app ^high parameter values shown in Fig. 2.