During initial several minutes after fertilization, sea urchin eggs exhibited high rate of respiration which was only slightly inhibited by cyanide. This cyanide-insensitive respiration was inhibited by calcium antagonists, diltiazem and verapamil, and calmodulin antagonists, N-(6-arninohexyl)-5-chloro-l-naphthalenesulfonmide hydrochloride (W-7), N-(6-aminohexyl)-1-naphthalenesulfonamide hydrochloride (W-5) and chlorpromazine, which were added within 1 min after insemination. The inhibitory effect of W-7 on cyanide-insensitive respiration was higher than that of W-5. Cyanidesensitive respiration of fertilized eggs observed after this initial period was not inhibited by these compounds. Ca2+ influx in eggs just after fertilization was inhibited by calcium antagonists but was rather enhanced by calmodulin antagonists.Fertilization-induced stimulation of cyanideinsensitive respiration probably results from calmodulin-dependent reactions which are activated by Ca2+ influx.It has been demostrated that fertilization induces in sea urchin eggs a marked increase in the respiratory rate followed by a gradual decrease to a steady rate of respiration (1, 2). This transient burst of respiration induced 'by fertilization is somewhat insensitive to cyanide (3, 4) and is accompanied by H202 production (5). H202 production probably occurs at the expense of mollecular oxygen. This burst of cyanide-insensitive respiration is followed by cyanidesensitive respiration with a higher steady rate than in unfertilized eggs. These indicate that fertilization stimulates in sea urchin eggs at first a cyanide-insensitive respiratory system(s) and then a cyanide-sensitive respiratory system, probably mitochondiral respiratory chain (4). However, the mechanisms of stimulation of these systems by fertilization remain unknown at present.In Arbacia eggs, which contain a quite large amount of echinochromes, Ca2+-induced oxidation of echinochromes has been found to cause oxygen consumption which is not sensitive to cyanide (6). Fertilization-induced Ca2+ increase (7) may cause a stimulation of oxygen consumption at the expense of echinochromes. However, this respiration may be limited to species of eggs which contain large amount of echinochromes. In many species of sea urchin other than Arbacia, unfertilized eggs contain quite low amounts, if any, of echinochromes.
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