Fig. 4. Effects of KN-93, a selective Ca²⁺/calmodulin kinase II (CaM kinase II) antagonist. (A) Two control responses to 10 µmoll^-1 levamisole (Lev) and two responses in the presence of 10 µmoll^-1 KN-93. Notice that the peak responses in the presence of KN-93 are smaller than the control responses. (B) Effect of KN-93 on acetylcholine (ACh) is slowly reversible. The figure illustrates the antagonistic effect of 10 µmoll^-1 KN-93 on the peak membrane potential responses to 10 µmoll^-1 acetylcholine. Notice that 20 min was required in this preparation before the response to acetylcholine was clearly returning towards the control level. This may reflect the lipophilic nature of KN-93 and the long time required to wash the drug from the preparation.