Figure 1.

Cd²⁺ modification of V391C channels. (A) Sequence alignments of TM6 and proximal cytoplasmic residues of rSK2, Shaker B, and the proton-gated bacterial K⁺ channel KcsA. The homologous glycine representing the glycine gating hinge in MthK is indicated by the asterisk. Numbered lines indicate residues of particular importance (see Results). (B and C) 5 μM Cd²⁺ was applied five times (dashes, 2s duration each application) to the inside face of an inside-out patch containing V391C channels in either the open state (B, 2 μM free Ca²⁺) or closed state (C, nominally Ca²⁺-free solution) at 0 mV. Lines above the traces indicate when channels were open (O) or closed (C), and the dashed lines below the traces indicate the zero current level. (D) Current amplitude after each 2-s application was measured, normalized to the maximum current before application, and plotted versus time to determine the modification time course for n > 5 patches in the open (open circles) and closed (closed circles) states.