Bioelectric responses of the echinoderm egg to fertilization.
The fertilization reaction of echinoderm eggs (Lytechinus pictus, a sea urchin, and Dendraster excentricus, a sand dollar) was followed with intracellular electrodes. Membrane potential and K(+) activity were recorded. The unfertilized egg of Lytechinus has a membrane potential of -8 mV, inside negative. Within 5 sec after the addition of sperm, a fertilization action potential develops, going to +10 mV, inside positive. The time from the initial depolarization to a return to the original -8 mV is 120-150 sec. The repolarization continues until a potential of -10 to -14 mV is reached, at which point it pauses for 3-4 min. At 6-8 min after fertilization, a further and relatively rapid hyperpolarization begins, going to -60 to -65 mV by 15-25 min after fertilization and remaining constant at these values. The membrane potential of the unfertilized egg appears to depend on a general permeability to anions. The fertilization action potential seems to reflect a prolonged influx of sodium. The final depolarization to -60 mV is attributable to the development of potassium conductance. Simultaneous measurements with a K(+) ion-selective electrode gives constant readings of about 240 mM K(+) in the unfertilized eggs throughout the fertilization process. Similar results were obtained with Dendraster eggs. The resting potential of the unfertilized eggs was -7 mV; the action potential on activation attained +18 mV; the repolarization paused at -16 to -24 mV and the final potential attained was -70 mV. The electrical changes after fertilization with spermatozoa or activation with Pronase were identical.
D000200:Action Potentials; D000818:Animals; D001693:Biological Transport, Active; D002463:Cell Membrane Permeability; D004447:Echinodermata / Q000502:physiology*; D004567:Electrodes, Implanted; D005260:Female; D005306:Fertilization; D007477:Ions; D008564:Membrane Potentials / Q000187:drug effects; D010063:Ovum / Q000502:physiology*; D011188:Potassium; D011402:Pronase / Q000494:pharmacology; D012617:Sea Urchins / Q000502:physiology; D012964:Sodium / Q000378:metabolism
D007477:Ions; D012964:Sodium; D011402:Pronase; D011188:Potassium