Purity >98%. Paxilline is an indole diterpene from fungi which potently and reversibly inhibits large conductance Ca2+ -activated K+ (BKCa) channels, as shown in patch clamp (Ki = 1.9 nM) and whole smooth muscle cell studies (Ki = 35.7 nM). It also enhances the binding of charybdotoxin, a peptidyl neurotoxin, to BKCa channels. Paxilline is currently used to evaluate the role of BKCa channels in various cell processes and responses.