High Quality Content by WIKIPEDIA articles! BK channels (Big Potassium), also called Maxi-K or slo1, are ion channels characterized by their large conductance of potassium ions (K+) through cell membranes. These channels are activated (opened) by changes in membrane electrical potential and/or by increases in concentration of intracellular calcium ion (Ca2+). Opening of BK channels allows K+ to passively flow through the channel, down the electrochemical gradient. Under typical physiological conditions, this results in an efflux of K+ from the cell, which leads to cell membrane hyperpolarization (a decrease in the electrical potential across the cell membrane) and a decrease in cell excitability (a decrease in the probability that the cell will transmit an action potential).