Fig. 4. Differential sensitivity of the three Ca²⁺ wave pacemakers of ascidian eggs (Phallusia) to mitochondrial inhibitors. (A-D) Effects of FCCP applied before fertilization (A, n=3) and during the period of activity of the Ca²⁺ wave pacemaker PM2 (B, n=4) inhibits PM2 activity. Perfusion of FCCP after extrusion of the second polar body (pb2) (C, n=3) produces a Ca²⁺ transient. Perfusion of FCCP during the period of activity of the Ca²⁺ wave pacemaker PM3 (D, n=4) affects pacemaker PM3 only slightly after 4 minutes. Perfusion of CN^- during the period of activity of PM1 (E) or PM2 (F,G) in eggs injected with CG/TR only (E, n=4) or with CG/TR and cATP (in F). Artificial production of ATP by UV flash photolysis of cATP (black arrowheads) restores partially PM2 activity (F, n=3). In eggs preincubated for 20 minutes in oligomycin before fertilization (G, n=3), Ca²⁺ wave pacemaker PM2 is still sensitive to CN^- perfusion. Artificial production of ATP by UV flash photolysis of cATP (black arrowheads) increases the frequency of the repetitive waves emitted by Ca²⁺ wave pacemaker PM2 (H, n=4). The periods for waves 1 to 4 (i.e. before the photorelease of ATP) and for waves 5 to 8 (i.e. after the photorelease of ATP) are indicated in the inset.