Pseudo-streaming potentials in Necturus gallbladder epithelium. II. The mechanism is a junctional diffusion potential

Area of Science:

• Epithelial physiology
• Membrane transport
• Cellular biophysics

Background:

• Apparent streaming potentials are observed in Necturus gallbladder epithelium upon changes in apical solution osmolality.
• The underlying mechanisms, particularly the role of osmotic water flow and solute concentration changes, require clarification.

Purpose of the Study:

• To elucidate the mechanisms of apparent streaming potentials induced by osmotic gradients in Necturus gallbladder epithelium.
• To differentiate between true streaming potentials and junctional diffusion potentials.
• To investigate the relationship between osmotic water flow and solute-solvent coupling across the epithelium.

Main Methods:

• Measured transepithelial voltage (Vms) changes.
• Assessed apical cell surface osmolality using a tetrabutylammonium ([TBA+])-selective microelectrode.
• Determined intracellular impermeant solute concentration ([TMA+]i) using a TMA(+)-selective microelectrode.
• Analyzed data using a mathematical model of epithelial transport.

Main Results:

• Time courses of Vms changes mirrored intracellular solute concentration changes, not apical solution osmolality changes.
• Apparent streaming potentials correlate with salt concentration shifts in lateral intercellular spaces, driven by osmotic water flow.
• Elevations in apical solution osmolality rapidly reduced junctional ionic selectivity.

Conclusions:

• The observed Vms changes are pseudo-streaming potentials, arising from junctional diffusion potentials secondary to osmotic water flow.
• Results do not support junctional solute-solvent coupling during transepithelial osmotic water flow.
• The study provides insights into epithelial ion and water transport regulation.