Passive H+/OH- permeability in epithelial brush border membranes.

Area of Science:

• Biochemistry
• Cell Biology
• Physiology

Background:

• Passive hydrogen ion (H+) and hydroxyl ion (OH-) permeability across epithelial cell membranes is rapid.
• This permeability contributes to the dissipation of H+/OH- gradients generated by cellular transport mechanisms.
• Multiple mechanisms facilitate H+/OH- transport, including lipid diffusion and protein-mediated pathways.

Purpose of the Study:

• To investigate the mechanisms and characteristics of passive H+/OH- permeability in different epithelial tissues.
• To compare passive H+/OH- permeability in renal proximal tubule and human placental brush border vesicles.
• To model the physiological significance of passive renal H+/OH- transport in cell pH regulation.

Main Methods:

• Utilized pH electrode recordings, pH-sensitive fluorescent probes, and magnetic resonance probes to study transport mechanisms.
• Examined passive H+/OH- permeability in biomembrane vesicles from renal proximal tubules and human placenta.
• Developed mathematical models to simulate proximal tubule acidification and pH regulation.

Main Results:

• Passive H+/OH- permeability in renal proximal tubule brush border vesicles resembles that of pure lipid bilayers, with minimal slippage through transporters or water channels.
• In contrast, human placental brush border vesicles exhibit H+/OH- permeability partially mediated by a stilbene-sensitive membrane protein.
• Mathematical modeling demonstrated the physiological impact of altered H+/OH- permeability on renal cell pH regulation.

Conclusions:

• Passive H+/OH- permeability varies significantly between different epithelial tissues.
• Renal proximal tubule H+/OH- permeability is primarily passive and lipid-based, while placental permeability involves specific proteins.
• Understanding these transport mechanisms is crucial for comprehending cellular pH homeostasis and its regulation.