Na+ binding to the Na(+)-glucose cotransporter is potential dependent

Area of Science:

• Cellular physiology
• Biophysics
• Molecular transport

Background:

• The Na(+)-glucose cotransporter (SGLT) plays a crucial role in glucose reabsorption in epithelial cells.
• Understanding the kinetics and voltage dependence of SGLT activity is essential for comprehending renal and intestinal glucose transport.

Purpose of the Study:

• To investigate the kinetic properties and membrane potential dependence of the Na(+)-glucose cotransporter (SGLT) in LLC-PK1 epithelial cells.
• To elucidate the rate-limiting steps in the SGLT transport cycle.

Main Methods:

• Whole-cell patch-clamp recording to measure sugar-induced currents (IAMG).
• Standardization of currents to cell capacitance for cell-size normalization.
• Kinetic analysis using Michaelis-Menten and Hill equations to determine kinetic parameters and Na+ concentration dependence.

Main Results:

• Sugar-induced currents (IAMG) exhibited Michaelis-Menten kinetics with respect to alpha-methylglucoside (AMG) concentration.
• Na+ concentration dependence followed the Hill equation with a coefficient of 1.6, indicating cooperative binding.
• Maximal transport rate (Im) was dependent on membrane potential, suggesting a voltage-dependent step beyond Na+ binding.

Conclusions:

• The Na(+)-glucose cotransporter's maximal transport rate is influenced by membrane potential.
• Both Na+ binding and at least one other step in the transport cycle are potential-dependent.
• The rate of Na+ binding to the transporter is also modulated by membrane potential.