Apamin is an 18 amino acid globular peptide neurotoxin found in apitoxin (bee venom).  Dry bee venom consists of 2–3% of apamin. Apamin selectively blocks SK channels, a type of Ca-activated K channel expressed in the central nervous system. Toxicity is caused by only a few amino acids, in particular cysteine, lysine, arginine, arginine and histidine. These amino acids are involved in the binding of apamin to the Ca-activated K channel. Due to its specificity for SK channels, apamin is used as a drug in biomedical research to study the electrical properties of SK channels and their role in the afterhyperpolarizations occurring immediately following an action potential.