Auxiliary protein of the large-conductance, voltage and calcium-activated potassium channel (BK alpha). Required for the conversion of BK alpha channels from a high-voltage to a low-voltage activated channel type in non-excitable cells. These are characterized by negative membrane voltages and constant low levels of calcium.
Isoform 1 is expressed highly in normal prostate and salivary gland, very weakly in colon, pancreas, and intestine, and not at all in other tissues. Isoform 1 is expressed highly in many cancer cell lines and in breast cancer, pancreatic cancer and colon cancer. Isoform 2 is expressed in cancer cell lines.