Penitrem A is a tremorgenic fungal toxin that acts as an inhibitor of the large conductance calcium-activated potassium channel BKCa (SLO1, Maxi-K, KCa1.1), inhibiting the binding of charybdotoxin with an IC50 value of 1.7 μM. It is currently used to evaluate the role of BKCa-mediated potassium flux in various cell processes and responses.