Voltage-gated K+ channels are important determinants of neuronal membrane excitability. Moreover, differences in K+ channel expression patterns and densities contribute to the variations in action potential waveforms and repetitive firing patterns evident in different neuronal cell types. The delayed rectifier-type (IK) channels (Kv1.5, Kv2.1, and Kv2.2) are expressed on all neuronal somata and proximal dendrites and are also found in a wide variety of non-neuronal cells types including pancreatic islets, alveolar cells and cardiac myocytes. Kv2.1 and Kv2.2 form distinct populations of K+ channels and these subunits are thought to be primarily responsible for IK in superior cervical ganglion cells.