Changes in cell volume measured with an electrophysiologic technique.

Area of Science:

• Cell biology
• Physiology
• Membrane transport

Background:

• The gallbladder epithelium regulates water transport.
• Understanding the hydraulic permeability of cell membranes is crucial for comprehending fluid balance.
• Previous studies have utilized various methods to assess membrane properties.

Purpose of the Study:

• To determine the hydraulic permeability coefficient (Lp) of the apical membrane of Necturus maculosus gallbladder epithelial cells.
• To investigate the role of apical membrane water permeability in transepithelial water transport.
• To estimate the unstirred layer thickness at the apical membrane surface.

Main Methods:

• Epithelial cells were loaded with tetramethylammonium (Me4N+) using nystatin.
• Intracellular Me4N+ concentration was measured with ion-sensitive microelectrodes.
• Cell volume changes were induced by altering mucosal solution osmolality to estimate Lp.

Main Results:

• The minimum hydraulic permeability coefficient (Lp) of the apical membrane was determined to be 1-3 X 10(-3) cm.sec-1.(osmoles/kg)-1.
• An osmolality difference of 1-3 milliosmoles/kg across the apical membrane could account for average transepithelial water transport.
• Optical measurements corroborated the calculated Lp values.
• The effective thickness of the apical unstirred layer was estimated, indicating diffusion delays.

Conclusions:

• The apical membrane of Necturus maculosus gallbladder epithelial cells exhibits significant hydraulic permeability.
• Water transport across the apical membrane is sensitive to small osmotic gradients.
• The findings provide insights into the biophysical properties of epithelial cell membranes and their role in fluid transport.