Electrical response to fertilization in ascidian oocytes

Area of Science:

• Developmental Biology
• Cellular Electrophysiology
• Reproductive Biology

Background:

• The fertilization potential (FP) is a crucial electrical event in many marine invertebrate oocytes.
• Ascidian oocytes present a unique model for studying fertilization due to distinct electrophysiological properties.

Purpose of the Study:

• To investigate the electrophysiological characteristics of ascidian oocyte fertilization.
• To determine if intrinsic mechanisms exist to prevent polyspermic fertilization in ascidians.

Main Methods:

• Utilized two intracellular electrodes to record membrane potentials and resistance in ascidian oocytes.
• Induced polyspermic fertilization through manipulation of extracellular coats, oocyte aging, and sperm density.
• Compared fertilization potentials and membrane resistance changes in monospermic and polyspermic conditions.

Main Results:

• Identified two classes of ascidian oocytes based on resting potential (RP): low RP (-20 to -35 mV) and high RP (-80 to -90 mV).
• Observed distinct fertilization potentials (FP) for each oocyte class, with high RP oocytes exhibiting regenerative potentials.
• Demonstrated a significant decrease in membrane resistance during FP plateau, independent of original RP, but not upon artificial depolarization.
• Found comparable FPs in monospermic and polyspermic fertilization, with no correlation between additional sperm and electrical events.

Conclusions:

• Ascidian oocytes possess diverse electrophysiological responses to fertilization.
• The plasma membrane of ascidian oocytes appears to lack inherent electrical or other mechanisms to prevent polyspermic fertilization.