Negative potential level in the outer layer of the toad skin.

Area of Science:

• Physiology
• Biophysics
• Membrane Transport

Background:

• The electrical properties of amphibian skin are crucial for understanding ion transport and barrier function.
• Microelectrode impalement provides a method to probe electrical potentials within biological tissues.

Purpose of the Study:

• To characterize the voltage profile of isolated toad skin (Bufo marinus ictericus) using microelectrode impalement.
• To investigate the influence of external ion concentrations and pH on superficial intraepithelial potential difference (PDi).

Main Methods:

• Impaling isolated toad skin with glass microelectrodes filled with 3 M KCl.
• Measuring potential difference (PDi) as a function of impalement depth.
• Varying external Na2SO4, K2SO4 concentrations, and pH to assess their effects on PDi.

Main Results:

• A continuous voltage profile was observed, with PDi showing a minimum negative value at approximately 6 µm depth.
• PDi exhibited a logarithmic dependence on external Na2SO4 or K2SO4 concentration.
• External acidification led to a reduction in negative PDi, becoming positive at pH 3.

Conclusions:

• PDi is interpreted as a diffusion potential arising from KCl diffusion from the microelectrode into the stratum corneum.
• Differences in potassium (K) and chloride (Cl) mobility, influenced by fixed charges and external pH, underlie PDi generation.
• The findings provide insights into the electrical characteristics and barrier properties of toad stratum corneum.