. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. a—- + mV 10 min h. JO ^ec^ _70 mV Figure 4. Fertilization potential of an egg in sea water whose resting potential was -15 mV. at fertilization appears to be the ionic basis for the fertilization potential. This hypothesis is supported by recordings of fertilization potentials generated by eggs inseminated in sodium and calcium-depleted sea water. In low ( mA/) sodium (choline-sub- stituted sea water), the membrane of the unfertilized egg is electrically excitable and can generate action potentials of briefer than no
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. a—- + mV 10 min h. JO ^ec^ _70 mV Figure 4. Fertilization potential of an egg in sea water whose resting potential was -15 mV. at fertilization appears to be the ionic basis for the fertilization potential. This hypothesis is supported by recordings of fertilization potentials generated by eggs inseminated in sodium and calcium-depleted sea water. In low ( mA/) sodium (choline-sub- stituted sea water), the membrane of the unfertilized egg is electrically excitable and can generate action potentials of briefer than normal duration upon stimulation (Fig. 5). After insemination these eggs fire a very brief action potential, and the fertilization potential (both segments a and h) is suppressed greatly. In low calcium sea water, the first component (segment a) of the fertilization potential is suppressed (Fig. 6). These findings show that both calcium and sodium influx generate the first response phase (segment a) of the fertilization potential, while sodium influx generates the second response phase (segment h). These electrophysiological studies make it possible to predict key properties of the rapid electrical block to polyspermy: (1) Unfertilized eggs that are not electrically excitable and/or that have low (-10 to —20 mV) resting potentials are abnormal or damaged, and should be susceptible +100 0 0 :r^JlJL__ 0 mV 0 mV -t-l mV. UNFERTILIZED FERTILIZED 10 tec Figure 5. Action potential and fertilization potential recorded in an egg cultured in choline substituted sea water containing mAf Na^. Action potentials of briefer than normal duration (compare with Fig. 3A, above) were elicited in the unfertilized egg (left) by pulses of 65 pA s and 100 pA 100 ms duration. The same egg (right) after Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may
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