Figure 5. The effect of [K⁺]_o on the rate of inactivation of fKv1.4[V561A] channels.

A and B, representative traces from a two pulse protocol (shown as inset of Fig. 2) on fKv1.4[V561A] channels at 2 mm[K⁺]_o (A) and 98 mm[K⁺]_o (B). Currents are scaled so that the peak of the P1 current elicited at +50 mV in both cases is the same size. C, inactivation of Kv1.4[V561A] channels is best fitted with a bi-exponential function. Changing [K⁺]_o from 2 (filled bar) to 98 mm (open bar) has little effect on the fast time constant, τ_fast (upper panel), or the slow time constant, τ_fast (middle panel), of inactivation of Kv1.4[V561A] channels. Over the range +10 to +50 mV, τ_fast is 199.73 ± 4.42 ms (n= 5) in 2 mm[K⁺]_o and 210.11 ± 6.49 ms (n= 5) in 98 mm[K⁺]_o. Over the range +10 to +50 mV, τ_slow is 1.623 ± 0.052 s (n= 5) in 2 mm[K⁺]_o and 1.523 ± 0.055 s (n= 5) in 98 mm[K⁺]_o. The ratio of the amplitudes of the two time constants, A_slow/A_fast is significantly affected by changing [K⁺]_o (bottom panel, significant differences denoted by asterisks, P < 0.01). Over the range +10 to +50 mV, in 2 mm[K⁺]_oA_slow/A_fast is 1.147 ± 0.050, and in 98 mm[K⁺]_oA_slow/A_fast is 0.759 ± 0.028 (n= 5, P < 0.001).