K_Ca3.1 (KCNN4, SK4) is a member of the Ca²⁺ activated K⁺ channel family that shares the characteristic of being activated by intracellular Ca²⁺. The channel has an intermediate conductance, is voltage insensitive and is activated by Ca²⁺ in the submicromolar range. The channel has a similar topology to that of K_V channels, that is, six transmembrane domains and intracellular N- and C-termini. 

K_Ca3.1 is widely expressed in epithelial, endothelial and cells of hematopoietic origin. In erythrocytes (red blood cells) it has been identified as the molecular correlate of the so-called Gardos channel.  

The functional role of the channel is to set the cell membrane potential at negative values so as to aid in the electrochemical transport of other ions such as Cl^- and Ca²⁺. Indeed, K_Ca3.1 has a key role in sustaining the Ca²⁺ influx in activated T lymphocytes and in regulating Cl^- secretion from colon epithelium. Therefore, specific blockers of the K_Ca3.1 channel have been proposed for the treatment of several diseases including autoimmune diseases, secretory diarrhea and sickle cell anemia.