KCa4.1 (Slack, Na+ activated K+ channel, Slo2.2, KCNT1) was originally cloned and named so due to its high similarity to the Slo genes1. Shortly after its discovery, KCa4.2 (Slick, Slo2.1, KCNT2), its sister channel was also cloned2. Although KCa4.2 (like KCa4.1) is functionally a Na+-activated K+ channel (KNa), it is termed KCa by the IUPHAR nomenclature, due to its sequence homology to other KCa channels. Both channels are activated by high intracellular concentrations of Na+.