Cell-permeable. KN-93 is a potent inhibitor of Ca²⁺/calmodulin-dependent kinase type II (CaM kinase II) (IC₅₀ = 0.37 μM). It does not affect the activities of PKA, PKC, MLCK, or Ca2+-phosphodiesterase. Also a direct extracellular open channel blocker of voltage-gated potassium channels (IC₅₀ = 307 nM for Kv1.5). More recently, KN-93 has been used to implicate roles for CaMKII in Ca2+-induced Ca2+ release in cardiac myocytes.