Figure 3.

Mg²⁺ modulates deactivation kinetics by binding between S2 and S3. (A) Sequences of S2 and S3 segments from voltage-gated K⁺ channels have been aligned. Acidic residues conserved throughout the voltage-gated channel superfamily are shown in green; acidic residues conserved only in the eag subfamily of K⁺ channels are shown in red. Sequences from eag family members, representative members of the K_v1 and K_v2 families, and a chimeric channel in which the K_v2.1 voltage sensor paddle has been inserted into K_v1.2 are included.³¹,³³,³⁴,⁴² Members of the eag subfamily contain acidic amino acids in S2 and S3 that are not present in other voltage-gated K⁺ channels.³⁰ Numbering is shown for HERG, d-eag and the chimeric channel sequences. Abbreviations used are: h, human; d, Drosophila; r, rat; erg, eag-related gene; elk, eag-like K⁺ channel gene. (B) Tail currents evoked upon return to −70 mV from +40 mV for single mutants or +60 mV for double mutants in the absence (black trace) or presence (red trace) of 10 mM Mg²⁺ have been scaled and superimposed to compare the time course of deactivation. Tail currents were fitted with single or double exponential components (thin dashed lines). Bars: 100 ms. The bath solution contained 96 mM NaCl, 2 mM KCl, 0.5 mM CaCl₂, 5 mM HEPES, pH 7.5.