Phlorizin binding to isolated enterocytes: membrane potential and sodium dependence

Area of Science:

• Biochemistry
• Cell Physiology
• Membrane Transport

Background:

• Phlorizin is a known inhibitor of glucose transporters.
• Understanding phlorizin binding provides insights into glucose transport mechanisms.

Purpose of the Study:

• To investigate the kinetics and regulation of phlorizin binding in isolated chick intestinal epithelial cells.
• To elucidate the roles of sodium ions and membrane potential in phlorizin-ligand interactions.

Main Methods:

• Utilized ATP-depleted intestinal epithelial cells for controlled ionic gradient manipulation.
• Assayed phlorizin binding at steady state under varying sodium concentrations and membrane potentials (delta psi).
• Defined carrier-specific binding by D-glucose inhibition.

Main Results:

• Phlorizin binding exhibited Michaelian kinetics, indicating a single homogeneous binding site.
• Sodium concentration and delta psi modulated apparent binding affinity, not maximum binding capacity.
• Sigmoidal activation by sodium and phlorizin-dependent maximum binding sites were observed.
• Phlorizin/sodium stoichiometry was determined to be 2:1.
• Translocation or sodium binding were proposed as delta psi-dependent steps.

Conclusions:

• Phlorizin binding is a complex process regulated by both sodium ions and membrane potential.
• The findings suggest a specific stoichiometry and provide models for the role of membrane potential in transporter function.
• This research enhances understanding of intestinal glucose absorption mechanisms.