K+ selective channels are some of the most widespread ion trafficking molecules in living organisms, with more than 70 genes encoding different K+ channels in humans. KV channels fall into one of the two classical categories of delayed rectifier (DR) and A-type. Delayed rectifier was the original name attributed to voltage-dependent K+ channels due to their delayed activation in squid giant axons. A-type channels are low voltage-activated, fast inactivating (therefore, transient) K+ channels. Specific KV toxins are often used to dissect the particular contribution of different subunits to native currents.