Time and voltage windows for reversing the electrical block to fertilization

Area of Science:

• * Marine Biology
• * Developmental Biology
• * Cell Physiology

Background:

• * Fertilization in sea urchins is a complex process involving cellular and molecular events.
• * Egg membrane potential plays a critical role in regulating fertilization.
• * Previous studies indicated an electrical block to fertilization under certain potential conditions.

Purpose of the Study:

• * To investigate the role of egg membrane potential in fertilization.
• * To determine the electrical properties of the fertilization block in Lytechinus pictus.
• * To characterize the kinetics and properties of the electrically sensitive step in fertilization.

Main Methods:

• * Voltage-clamping of Lytechinus pictus eggs to control membrane potential.
• * Application of brief inside-negative electrical pulses to overcome fertilization block.
• * Systematic variation of pulse duration and voltage to analyze fertilization properties.

Main Results:

• * Fertilization block at positive membrane potentials (+15 mV) can be overcome by brief inside-negative potentials.
• * An electrically sensitive step is initiated within milliseconds (30-60 msec at -60 mV) of inside negativity.
• * Potential-independent steps occur alongside the electrically sensitive step, with faster completion via paired pulses.

Conclusions:

• * Brief periods of inside-negative membrane potential are sufficient to initiate and complete the electrically sensitive step of fertilization.
• * The permissive state for fertilization is established more rapidly by inside negativity than the non-permissive state by inside positivity.
• * The timing and variability of subsequent activation events suggest complex downstream signaling pathways.