Forms a voltage-independent potassium channel activated by intracellular calcium (PubMed:11533126, PubMed:11245600). Activation is followed by membrane hyperpolarization (PubMed:11533126). Thought to regulate neuronal excitability by contributing to the slow component of synaptic afterhyperpolarization (PubMed:11533126). Inhibited by bee venom neurotoxin apamin. 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 (By similarity). Interacts with CALM1 (By similarity). Belongs to the potassium channel KCNN family. KCa2.3/KCNN3 subfamily.