Fig. 1. Pharmacological inhibition of CamKII, but not PKC, blocked exit from meiosis. (A) To induce completion of meiosis, eggs were incubated in Sr²⁺ medium supplemented with doses of KN-93 (CamKII inhibitor), KN-92 (the inactive analogue of KN-93) or BIM1 (PKC inhibitor). Only KN-93 prevented exit from meiosis. (B) Eggs were induced to resume meiosis by PLC cRNA microinjection, in a range of concentrations of KN-93-supplemented media. The CamKII inhibitor blocked meiotic progression over a similar dose range as that observed with Sr²⁺ medium. (C) KN-93 inhibited Ca²⁺ spiking. Intracellular Ca²⁺ changes were recorded in eggs incubated in Sr²⁺ media supplemented with 10 µM KN-93. All eggs that failed to activate (n=35) also failed to exhibit Ca²⁺ spiking; however, all those eggs that extruded a second polar body and formed pronuclei (n=10) had one or more Ca²⁺ spikes. Percentage activation rates were assessed at 8 hours by the formation of pronuclei. The number of eggs used is indicated in parenthesis.