potassium intermediate/small conductance calcium-activated channel, subfamily N, member 1 Synonyms: SK1 kcnn1. Symbol: Kcnn1
Ca2+-activated K+ channels are activated by rises in
intracellular Ca2+. The KCa potassium channel family includes
at least three subfamilies, KCa1–3 . Channels containing the
KCa1.1 alpha-subunit (BK channels) have large single channel conductance and are maximally activated by micromolar concentrations of intracellular free calcium and concurrent depolarization. Their kinetic and pharmacological properties are
modified upon assembly with membrane standing beta-subunits
. The KCa2 subfamily of small conductance Ca2+-activated
K+ channels, also known as SK channels, has three closely
related members SK1 (KCa2.1), SK2 (KCa2.2), and SK3 (KCa2.3),
which are characterized by a small single channel conductance.
The IK channel (KCa3.1) shows an intermediate single channel
conductance. Both SK and IK channels are voltage-independent and activated by submicromolar concentrations of intracellular free Ca2+. The gating of SK and IK channels is induced
upon Ca2+ binding to calmodulin, which is constitutively
bound to each channel subunit. Ca2+ binding to calmodulin
induces a conformational change, which leads to the opening of
these channels , , .
Kcnn1 : potassium intermediate/small conductance calcium-activated channel, subfamily N, member 1
The bee venom toxin
apamin inhibits exclusively the three cloned SK channel subtypes (SK1, SK2, and SK3) with different affinity, highest for
SK2, lowest for SK1, and intermediate for SK3 channels. 
The alkaloid methyl-laudanosine blocks SK1, SK2 and SK3 currents with equal potency, IK currents were unaffected. 
SK channels consist of heterotetrameric subunit assembly of four identical subunits that associate to form a symmetric tetramer SK channels . Each of the subunits have six transmembrane segments (S1-S6) and intracellular N- and C-termini.4 However, SK2 channels only contain two positively charged amino acids in the S4 segment and are therefore insensitive to changes in membrane voltage. 
Crystallographic studies suggest that SK channels gate as a dimer-of-dimers, and that the physical gate of SK channels resides at or near the selectivity filter of the channels. In addition, Ca(2+)-independent interactions between the SK channel alpha subunits and calmoduline are necessary for proper membrane trafficking. 
SK1 is frequently associated with neuronal fibers and only occasionally detected in neuronal somata. 
Central nervous system
SK channels are widely expressed in the central nervous system , thereby potentially contributing to neuronal excitability control and they are critical regulators of neuronal excitability in hippocampus ).
SK1 is expressed, from highest to lowest levels in: amígdala, hippocampus, caudate nucleus, cerebellum , thalamus, substantia nigra, spinal cord and pituitary gland. . SK1 and SK2 are often expressed in the same neurons, predominantly in the neocortex, hippocampal formation, cerebellum, and thalamus ).
For further information about SK channels expression see table 1 Densities of immunoreactivity for SK1, SK2, and SK3 proteins in various compartments of the mouse central nervous system in Sailer et al., 2006 ).
SK1 is found in testis, ovary and aorta and in several pathological conditions such oligodendroglioma, glioblastoma and gastric tumour.
The SK channel-mediated current regulates membrane excitability, increases the precision of neuronal firing , and modulates synaptic plasticity by regulating excitatory synaptic transmission in the amygdala  and the
hippocampus . Inhibition of SK channels facilitates hippocampal independent  as well as dependent learning  and improves memory performance .