Forms a voltage-independent potassium channel activated by intracellular calcium (PubMed:8781233). Activation is followed by membrane hyperpolarization (By similarity). Thought to regulate neuronal excitability by contributing to the slow component of synaptic afterhyperpolarization (By similarity). Inhibited by bee venom neurotoxin apamin (PubMed:8781233). Inhibited by d-tubocurarine and tetraethylammonium (TEA) (By similarity). 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). Widely expressed including brain. Belongs to the potassium channel KCNN family. KCa2.1/KCNN1 subfamily.