Figure 2. Changes in Ca_i and pH_i during mitosis depend on external Ca⁺⁺ and Na⁺.

Eggs were transferred in the different media after fertilization (arrow). Two examples representative of n measurements (number in brackets) are shown in each condition. Variations in pH_i (a), evolution of Ca_i (b) and images of eggs taken 70 min after fertilization (insets in a). A. Transfer in 0Na (1), Am (2) or Ac (3). B. Effect of additional absence of external Ca after transfer in 0Na0Ca (1), Am0Ca (2) or Ac0Ca (3). C. Mean levels of pH_i (a) and Ca_i (b) changes recorded from 60–65 mins after sperm addition in Figs. A and B. pH_i changes (a) are expressed relative to that of unfertilized egg (arbitrarily taken as 1) while Ca_i changes (b) are expressed as the percentage of the fertilization Ca_i peak arbitrarily taken as 100 (zero is the unfertilized level). Values (means +/− sem) obtained in the absence of external Ca are significantly different (student test, p<0.01, two black stars) or not (ns, black letters) from control. Values obtained in the absence of Ca are significantly different (p<0.01, two grey stars) or not (ns, grey letters) from those obtained in the presence of Ca. Number of eggs is indicated for each condition (brackets).