The intermediate conductance Ca2+ – activated K+ channel on Qube 384
Ca2+-activated K+ channels (KCa) are integral players in setting the membrane potential and regulating Ca2+ homeostasis. The human genome consists of a total of 8 KCa channels that differ in their unitary conductance, genetic relation to each other and mechanism of Ca2+ binding. The channels are subdivided in two groups according to the aforementioned characteristics. The first group was initially characterized by their structural similarity and comprises of KCa1.1 (BK), KCa4.1, KCa4.2 and KCa5.1. Later studies revealed that these channels have in fact a different activation mode and only KCa1.1 (BK) is a truly Ca2+-activated channel aside from its voltage-dependence. The second group is characterized by their unitary conductance and encompasses three small conductance (SK) channels KCa2.1 (SK1), KCa2.2 (SK2) and KCa2.3
(SK3), and an intermediate-conductance channel KCa3.1 that is also known as SK4, IKCa1, IK-1 or KCa4 encoded by KCNN4 (Wei et al., 2005). KCa3.1 was cloned independently by three groups in 1997, therefore, the channels biophysical and pharmacological properties are already well-established (Wulff & Castle, 2010).