Physiological studies on fertilization and activation of fish eggs: V. The role of calcium ions in activation of Oryzias eggs

Abstract

1. 1. A few unfertilized eggs (5–6 per cent) of the medaka ( Oryzias latipes) reveal autoactivation in the isotonic Ringer's solution. The percentage of autoactivation markedly decreases in Ca-free Ringer's solution. No eggs show autoactivation in an isotonic oxalate solution or in oxalated Ringer's solution. 2. 2. When unfertilized eggs are treated with isotonic oxalate solution they lose the capacity for cortical changes on stimulation by pricking. These eggs show cortical response without further stimulation when transferred to Ringer's solution. 3. 3. The presence of calcium ions favors the cortical response of eggs on stimulation with sodium oleate and saponin. Only a few eggs show activation if the eggs are first treated with these chemical agents dissolved in Ca-free Ringer or in oxalate solution and then transferred to Ca-free media. 4. 4. The reaction of an exudate of cortical protoplasm with sodium alizarin sulfonate indicates that free calcium ions are released from the cortical protoplasm at the time of stimulation with pricking. Anesthetized eggs reveal only a slight reaction with the dye. 5. 5. Calcium ions are not necessary in the primary phase of activation; they are released from the cortical protoplasm at this phase. Calcium ions are necessary or at least have a favorable effect in the secondary phase of activation. 6. 6. The cortical changes involved in activation of Oryzias eggs may be expressed by the following catenary reactions: Stimulants → stimulation → fertilization-wave → breakdown of cortical alveoli → release of colloid from alveoli → separation of egg membrane. Calcium ions are released in stimulation and they may be necessary for the establishment of the fertilization-wave which causes the breakdown of the cortical alveoli.