KCNB1 forms tetrameric, potassium-selective channels through which potassium ions pass according to their electrochemical gradient. The channel switches between open and closed conformations in response to the voltage difference across the membrane. Homotetrameric channels carry a delayed-rectifier, voltage-dependent outward current with rapid activation and slow inactivation on membrane depolarisation. KCNB1 contributes to action potential repolarisation, duration and the frequency of repetitive firing in neurons, muscle cells and endocrine cells, and to homeostatic attenuation of electrical excitability across the brain.

The KCNB1 protein can assemble with KCNB2 in varying proportions, and with subunits that are non-conducting on their own, including KCNF1, KCNG1, KCNG3, KCNG4, KCNH1, KCNH2, KCNS1, KCNS2, KCNS3 and KCNV1. This produces a functionally diverse set of channel complexes. Ancillary beta subunits such as AMIGO1, KCNE1, KCNE2 and KCNE3 slow activation and inactivation. KCNB1 also promotes surface trafficking of KCNG3, KCNH1 and KCNH2. It is a major contributor to the slowly inactivating delayed-rectifier current in central nervous system neurons, sympathetic ganglion neurons, neuroendocrine cells, pancreatic beta cells, cardiomyocytes and smooth muscle cells. In hippocampal and cortical pyramidal neurons it slows firing during high-frequency stimulation. In pancreatic beta cells it limits calcium influx and insulin secretion. It may also confer neuroprotection against hypoxic or ischaemic insults, yet contributes to the pro-apoptotic potassium current surge in neuronal death after oxidative injury.

Independently of its electrical function, KCNB1 supports calcium-dependent recruitment and release of fusion-competent vesicles by binding components of the fusion machinery. The KCNB1 gene belongs to the Shab-related subfamily, the human counterpart of Drosophila shab, and is grouped by HGNC with the BTB domain-containing potassium channels. Its earlier name was potassium voltage-gated channel, Shab-related subfamily, member 1.