Forms a voltage-independent potassium channel activated by intracellular calcium (PubMed:8781233, PubMed:20562108). Activation is followed by membrane hyperpolarization. Thought to regulate neuronal excitability by contributing to the slow component of synaptic afterhyperpolarization. Inhibited by bee venom neurotoxin apamin (PubMed:8781233, PubMed:20562108). Inhibited by UCL 1684 and tetraethylammonium (TEA) (PubMed:20562108). Heterooligomer. The complex is composed of 4 channel subunits each of which binds to a calmodulin subunit which regulates the channel activity through calcium-binding. Brain. Belongs to the potassium channel KCNN family. KCa2.2/KCNN2 subfamily.