Streptomyces lividans potassium channel KcsA is regulated by the potassium electrochemical gradient

It is currently held that the Streptomyces lividans potassium channel, KcsA, requires an intracellular pH < 5 to exhibit activity in planar lipid bilayers. Here, we show that KcsA functions well at normal physiological pH in the presence of a potassium electrochemical gradient. Single-channel conductance and open probability increased directly as the extracellular potassium concentration was decreased. Channel activity was sensitive to both the membrane potential and the size of the gradient, thus indicating that gating of the channel depends on both components of the electrochemical potential. When [K-in(+)]/[k(ex)(+)] was 200mM/10mM, M ex chord conductance was 24 pS with subconductance 15 pS; open probability was 0.9. The permeability series was K+ > Rb+ >>> Cs+; K+ selectivity over Rb2+ was 1.2-fold and selectivity over Na+ was 12-fold. The channels were disrupted by intracellular Na+ and blocked by intracellular Ba2(+). A hypothetical supramolecular model for the channel is presented. (C) 2004 Elsevier Inc. All rights reserved.