Electrical fluctuations associated with active transport

Area of Science:

• Physiology
• Biophysics
• Membrane Transport

Background:

• Active transport of sodium ions across biological membranes is crucial for cellular function.
• Voltage fluctuations are inherent in biological systems and can provide insights into transport mechanisms.
• Frog abdominal skin is a well-established model for studying epithelial sodium transport.

Purpose of the Study:

• To investigate the origins and characteristics of voltage fluctuations during active sodium transport in frog abdominal skin.
• To differentiate the contributions of resistance and current fluctuations to the overall voltage fluctuations.
• To elucidate the role of specific transport components and temperature on these fluctuations.

Main Methods:

• Spectral analysis of voltage fluctuations in the 0.025-10 Hz band.
• Manipulation of transmembrane potential using an external current supply.
• Application of Ouabain to selectively inhibit Na+/K+-ATPase.
• Measurements conducted at different temperatures (20°C and 32°C).

Main Results:

• Voltage fluctuations diminished with decreasing potential but reached a minimum finite value, indicating contributions from both resistance and current.
• Ouabain abolished current fluctuations but not resistance fluctuations.
• At 20°C, spectral intensities of resistance and current fluctuations followed a power law (1/f^a, a=1.6-2.0).
• At 32°C, a sigmoid-shaped spectrum suggested a relaxation process with a time constant of 0.6 seconds.

Conclusions:

• Voltage fluctuations during active sodium transport are a composite of stochastic variations in membrane resistance and transport current.
• The findings suggest a carrier-mediated mechanism for sodium transport, involving stochastic variations in carrier-ligand complex concentrations.
• Temperature influences the dynamics of these fluctuations, potentially reflecting changes in carrier kinetics or membrane properties.