Membrane hyperpolarization activates trout sperm without an increase in intracellular pH

Area of Science:

• Reproductive Biology
• Cell Physiology
• Fish Biology

Background:

• Sperm motility initiation is crucial for fertilization.
• Trout sperm motility is regulated by extracellular potassium and membrane potential.
• Intracellular pH changes are implicated in sperm activation in other species.

Purpose of the Study:

• To investigate the role of membrane potential and intracellular pH in trout sperm activation.
• To elucidate the mechanisms by which potassium and divalent cations regulate trout sperm motility.
• To propose a model for trout sperm activation.

Main Methods:

• Utilized membrane potential-sensitive fluorescent dye (diS-C3-(5)) to measure potassium's contribution to membrane potential.
• Employed Cs+ and valinomycin to manipulate membrane potential.
• Used surface potential-sensitive dye (ANS) to measure divalent cation-induced surface potential masking.
• Assessed intracellular pH changes using pH manipulation techniques.

Main Results:

• Trout sperm motility is inhibited by high extracellular potassium and activated by its dilution, indicating membrane potential regulation.
• Divalent cations activate trout sperm in the presence of inhibitory potassium by masking membrane surface potential.
• Unlike other species, trout sperm activation is not regulated by increased intracellular pH; instead, a decrease is observed.
• Membrane hyperpolarization is proposed as the trigger for trout sperm activation.

Conclusions:

• Trout sperm activation is primarily regulated by membrane potential changes, specifically hyperpolarization.
• Divalent cations play a significant role in modulating sperm activation through surface potential effects.
• Intracellular pH is not a regulatory factor in trout sperm motility, differentiating it from sea urchin and mammalian sperm.