The electrical changes accompanying fertilization and cortical vesicle secretion in the medaka egg |
| |
Authors: | Richard Nuccitelli |
| |
Institution: | Department of Physiology, Medical School, University of California, Los Angeles, California 90024 USA |
| |
Abstract: | The electrical properties of the egg of the medaka, Oryzias latipes, were studied before, during, and after fertilization. The resting potential of the unfertilized egg averaged ?39 ± 9 mV in Yamamoto's Ringers (Y. Ringers), but 20% of the values were between ?50 and ?60 mV. Fertilization triggers a small depolarization of 4 ± 3 mV in 10% Y. Ringers with an average duration of 20 ± 10 sec. The amplitude of this depolarization is independent of Na+]o, Ca2+]o, and Cl?]o, so it appears to be due to a nonspecific leak triggered by sperm-egg fusion. The depolarization is followed by a longer hyperpolarizing phase with an average amplitude of 31 ± 12 mV. Recovery from this hyperpolarization has a fast phase lasting 155 ± 18 sec, followed by a slower phase which reaches a steady average membrane potential of ?19 ± 1 mV by 9 min after fertilization. The membrane resistance falls 10-fold during the first 2 min after fertilization, from 40 (1520 kΩ-cm2) to 3 MΩ. This is largely due to an increase in the K+ conductance. At the peak of the hyperpolarization, the membrane potential exhibits a 28 mV/decade K+]o dependence and a 6 mV/decade Na+]o dependence. The membrane resistance slowly recovers over the next 8 min to a value about 30% larger than before fertilization. The relation of current vs voltage was linear before, during, and after fertilization and indicated a reversal potential of ?98 ± 20 mV for the hyperpolarization peak. The egg's capacitance averaged 0.04 ± 0.01 μF (0.9 μF/cm2) before fertilization and approximately doubles within 90 sec after fertilization. It then decreases over a 9-min period, reaching a value 25% smaller than before fertilization. |
| |
Keywords: | |
本文献已被 ScienceDirect 等数据库收录! |
|