Fig. 6. Inhibition of Cdk1 activity does not decrease responsiveness to Ins(1,4,5)P₃. Pairs of eggs, A and B, were co-injected with 2 mM Ca²⁺ Green and 3.5 mM caged gPtdIns(4,5)P₂ [a slowly hydrolysable Ins(1,4,5)P₃ analogue] to give an intracellular concentration of approximately 20 µM Ca²⁺ Green and 35 µM gPtdIns(4,5)P₂,and Ca²⁺ increases were measured simultaneously. Flashes of UV light (purple stars) were administered in increasing duration until a significant rise in Ca²⁺ release was observed (flash number 1). This flash duration (750 milliseconds) was the duration used for all further flashes. (A) Control egg with no p21. (B) An egg injected with p21::HcRed protein (the red fluorescent variant was used to avoid interfering with the Ca²⁺ Green signal). Each egg was injected with sperm extract and once the control had started to give second phase oscillations, UV-light flashes (numbered 2-6) were delivered in between oscillations in the control (indicated by white 2 on black background symbols). The pale blue dashed lines emphasise synchronicity of each UV-light-flash-induced Ca²⁺ release. After the second phase oscillations had stopped in the control and a second polar body had been extruded, two further flashes (numbers 7 and 8) were given (n=7, six animals).