Effect of permeant and impermeant ions on inactivation. (A and B, upper left) Voltage protocols and representative traces for recovery at −60 mV from 2-ms (A) and 500-ms (B) steps to 0 mV. (A and B, lower left) Responses to conditioning and test steps at higher gain. (A and B, right) Fraction of available channels versus recovery interval for Purkinje and cerebellar nuclear neurons in high and low Na for 2-ms conditioning steps for PKJ high Na (N = 11), PKJ low Na (N = 6), CBN high Na (N = 10), and CBN low Na (N = 8), and for 500-ms conditioning steps for PKJ high Na (N = 8), PKJ low Na (N = 7), CBN high Na (N = 6), and CBN low Na (N = 5). (C, left) Data as in B, right, but for med PKJ cells. High Na (N = 6), low Na (N = 6). Data from wild-type PKJ cells are superimposed for comparison. (C, right) Increase in availability in high Na relative to low Na for wild-type PKJ, med PKJ, and wild-type CBN cells. (D, left) Voltage protocol and representative traces for currents in 100 mM NaCl, CsCl, or TEA-Cl from Purkinje cells. (D, right) Fraction of available channels versus recovery interval for 155 NaCl, (N = 11), 105 CsCl and 50 NaCl (N = 5), and 105 TEA-Cl and 50 NaCl (N = 6).