Extracellular K+ elevates outward currents through Kir2.1 channels by increasing single-channel conductance

► We study the regulation of outward Kir2.1 currents by [K+]o. ► [K+]o up-regulates single-channel conductance but not open probability. ► [K+]o-effect on outward Kir2.1 currents is not related to relief of channel block. ► [K+]o directly modulates K+ permeation in Kir2.1 channels.