KCa2.1 is a member of the Ca2+-activated K+ channels family with small conductance that includes KCa2.2 (SK2) and KCa2.3 (SK3). The channel is voltage insensitive and is activated by intracellular Ca2+ in the submicromolar range. It has a similar topology to that of voltage-dependent K+ channels (KV channels), that is six transmembrane domains and intracellular N- and C-termini.
KCa2.1 channel expression is roughly confined to neuronal tissue, although there are some indications that it may be present in non-neuronal tissues as well.
The sensitivity of KCa2.1 to the bee venom toxin Apamin (#STA-200) is a matter of some controversy. Expression of the human KCa2.1 in mammalian cell lines showed that most cells produce channels that can be blocked by Apamin. However, expression of KCa2.1 in Xenopus oocytes produced channels that were mostly insensitive to apamin. Interestingly, the rat KCa2.1 is unable to form functional channels when expressed alone in either cell lines or oocytes.
