The K_Ca1.1 channel (also known as KCNMA1, BK_Ca, Maxi K⁺ or slo) is part of a structurally diverse group of K⁺ channels that are activated by an increase in intracellular Ca²⁺. K_Ca1.1 shows a large single channel conductance when recorded electrophysiologically and hence its name. It differs from the rest of the subfamily members in that it can be activated by both an increase in intracellular Ca²⁺ and by membrane depolarization. In addition, the K_Ca1.1 channel structurally differs from the other Ca²⁺-dependent K⁺ channels. While the latter group has a topology that resembles that of the voltage-dependent K⁺ channels, the K_Ca1.1 channel has an extracellular N-terminus domain as well as an additional transmembrane domain.

K_Ca1.1 is expressed in virtually all cell types where it causes hyperpolarization and helps to connect intracellular Ca²⁺ signaling pathways and membrane excitability.

Indeed, K_Ca1.1 channels play a crucial role in smooth muscle contractility, neuronal spike shaping and neurotransmitter release.