Forms a voltage-independent potassium channel activated by intracellular calcium (PubMed:31155282, PubMed:20562108). 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. 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 (PubMed:31155282). The second poly-Gln region of KCNN3 is highly polymorphic and the number of Gln varies from 12 to 28 in the population. The disease is caused by variants affecting the gene represented in this entry. Do not produce functional channels, but selectively suppresses endogenous SK3 currents, in a dominant-negative fashion. This dominant inhibitory effect extends to other members of the SK subfamily. Widely distributed in human tissues and is present at 20-60% of SK3 in the brain. Belongs to the potassium channel KCNN family. KCa2.3/KCNN3 subfamily.