Cai and pHi depend on the presence of external HCO3–.

A. Observation 80 mins after fertilization. Eggs develop in ASW (Control) or are transferred 20 mins after fertilization into ASW deprived of Ca (0Ca), HCO3− (0HCO3) or of Na+ and Ca++ (0Na0Ca). B. Time course after fertilization of pHi (a) and Cai (b) in ASW, 0Na and 0Na0Ca in the presence or not of HCO3−. Examples of results obtained in absence of HCO3-, i.e. in 0HCO3 (1), 0Na0HCO3 (2) and 0Na0Ca0HC03 (3), are depicted in different grey colours and representative of n determinations (grey number in brackets). In each condition, one typical control experiment performed with the same population of eggs in the presence of HCO3−, i.e. in ASW (1), 0Na (2) and 0Na0Ca (3) is shown in black curve and representative of n determinations (black number in brackets).