Gating of two-pore domain K⁺ channels by extracellular pH

Potassium channels have a conserved selectivity filter that is important in determining which ions are conducted and at what rate. Although K⁺ channels of different conductance characteristics are known, they differ more widely in the way their opening and closing, the gating, is governed. TASK and TALK subfamily proteins are two-pore region KCNK K⁺ channels gated open by extracellular pH. We discuss the mechanism for this gating in terms of electrostatic effects on the pore changing the occupancy and open probability of the channels in a way reminiscent of C-type inactivation gating at the selectivity filter. Essential to this proposed mechanism is the replacement of two highly conserved aspartate residues at the pore mouth by asparagine or histidine residues in the TALK and TASK channels.