Forms a voltage-independent potassium channel activated by intracellular calcium (PubMed:11557517). Activation is followed by membrane hyperpolarization (PubMed:11557517). Thought to regulate neuronal excitability by contributing to the slow component of synaptic afterhyperpolarization (PubMed:11557517). Inhibited by bee venom neurotoxin apamin. Inhibited by d-tubocurarine and tetraethylammonium (TEA). 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 calmodulin. At least 16 isoforms may be produced by combinatorial splicing of the N-terminal exon 3.1 and the C-terminal exons 7, 8a and 9. Experimental confirmation may be lacking for some isoforms. Highest expression in brain and liver with lower levels in heart, testis, kidney and colon. In colon, detected in smooth muscle cells. Expressed in atrial and ventricular myocytes with higher levels in atrial myocytes. The poly-Glu region of KCNN1 is polymorphic and the number of Glu varies between strains (from 10 to 12). The repeat with 10 Glu residues (shown here) is found in BALB/c, DBA/2J, 129/SvJ, A/J, C3H/HeJ, BALB/cJ, BXD-31, SM/J, ST/BJ, FVB/NJ, NZB/B1NJ, CBA/J and CAST/Ei. Produced by alternative splicing events in which various combinations of the four 5' non-coding exons A, B1, B2 or C are joined directly to exon 3.2. Reduced calmodulin-binding. Reduced calmodulin-binding. Reduced calmodulin-binding. Reduced calmodulin-binding. Reduced calmodulin-binding. Reduced calmodulin-binding. Belongs to the potassium channel KCNN family. KCa2.1/KCNN1 subfamily.