Fig. 4. Effect of artificial [Ca²⁺]_i elevation on IP₃ production. A Ca²⁺-ionophore A23187 was applied to unfertilized H. pulcherrimus eggs in stdASW (A) or 0CaASW (B) to a final concentration of 10 µg/ml. Data for cGMP (white circles) and IP₃ (black circles) are averages of two experiments. Bars indicate the highest and lowest values. [Ca²⁺]_i time courses (broken line) are typical ones. [Ca²⁺]_i in stdASW (A) rose far higher than 3 µM (impossible to measure with indo-1), and 7-8 minutes later began to descend very slowly. More than 90% eggs were observed to form the fertilization envelope. Note that IP₃ levels rose along with the [Ca²⁺]_i increase, but cGMP levels did not change significantly.

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