Effects of sodium on beta-cell electrical activity

Area of Science:

• Cellular physiology
• Electrophysiology

Background:

• The role of sodium ions (Na+) in regulating pancreatic beta-cell membrane potential is crucial for insulin secretion.
• Understanding these ionic contributions is key to deciphering beta-cell function in health and disease.

Purpose of the Study:

• To investigate the specific contribution of external sodium (Na+) to the membrane potential of mouse pancreatic beta-cells.
• To elucidate the mechanisms underlying membrane potential changes upon sodium removal.

Main Methods:

• Intracellular microelectrode recordings were used to measure membrane potential in mouse pancreatic beta-cells.
• Experiments involved complete removal of external sodium and the addition of ouabain, with and without glucose.

Main Results:

• Complete external sodium removal did not affect spike peak potential but caused a negative shift in resting membrane potential.
• A two-phase hyperpolarization-depolarization pattern was observed after sodium removal, persisting with ouabain.
• Depolarization was associated with increased input resistance and decreased action potential rise rate (dV/dtmax).
• Post-burst hyperpolarization (PBH) was reactivated by low external sodium, even with ouabain.

Conclusions:

• A significant resting sodium permeability (PNa) exists in beta-cells, but voltage-gated sodium channels are not the primary drivers of action potentials.
• Membrane depolarization after sodium removal results from Na+-K+ pump inhibition and decreased potassium permeability (PK).
• The blockage of PBH in low sodium is due to PK inactivation, not Na+-K+ pump inhibition.