Fig. 1. (A) Sperm-triggered [Ca²⁺]_c oscillations during meiosis in an ascidian egg (Phallusia). The first series of Ca²⁺ oscillations is composed of the fertilization Ca²⁺ wave followed by four waves (PM1), which leads to the extrusion of the first polar body (pb1) about 5-7 minutes after sperm-egg fusion. After 2-4 minutes, the second series of Ca²⁺ oscillations (PM2) are triggered. These last 15-20 minutes, ending when the second polar body (pb2) is emitted. The values for [Ca²⁺]_c displayed on the right of the graph are from aequorin measurements (Speksnijder et al., 1989). (B) Variations of oxygen consumption during meiosis in ascidian eggs (Phallusia). Oxygen fluxes are measured on a single egg using the oxygen-sensitive self-referencing vibrating probe (upper images taken at t=0 and t=12 minutes). Sperm-egg fusion triggers a first increase in oxygen consumption, which peaks during the period of activity of Ca²⁺ wave pacemaker PM1 and lasts until the first polar body (pb1) is emitted. A second increase in oxygen consumption occurs during the period of activity of Ca²⁺ wave pacemaker PM2 and terminates when the second polar body is emitted (pb2) (n=7). The vertical bars in the graph represent average measurements of the oxygen consumption before fertilization (100%), after meiosis completion (126±15%) and during the activity of the pacemakers PM1 (167±18%) and PM2 (173±14%) (average from eight single eggs, five Phallusia and three Ciona). The transient increase in oxygen consumption observed between PM1 and PM2 in the example shown was not seen in other experiments. By contrast, two transient increases associated with the periods of pacemakers PM1 and PM2 activity were observed for every egg recorded. (C) Variations of oxygen consumption in an ascidian egg (Ascidiella) activated by caged Ins(1,4,5)P₃ (cIP₃) photolysis. Simultaneous measurements of [Ca²⁺]_c (using CG) and oxygen consumption (using the vibrating probe) show that each time intracellular Ins(1,4,5)P₃ is photoreleased by a UV flash (black arrowhead), it induces a Ca²⁺ transient accompanied by a transient activation of oxygen consumption (all 20 UV flashes applied to 6 different eggs generated similar responses in oxygen consumption). (D) Increase in oxygen consumption in an ascidian egg (Ascidiella) perfused with the mitochondrial uncoupler FCCP. The oxygen electrode is first positioned far from the egg (1) then brought close to the egg (2) to measure its basal oxygen consumption. A large increase in oxygen consumption is observed when FCCP is added to the dish to give a final concentration of 1 µM (bar under the graph).

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