Potential-dependent block of human delayed rectifier K+ channels by internal Na+

Area of Science:

• Neuroscience
• Cell Physiology
• Ion Channel Function

Background:

• Delayed rectifier K+ currents are crucial for neuronal excitability.
• SH-SY5Y neuroblastoma cells provide a model for studying neuronal ion channel behavior.
• The role of intracellular ions in modulating K+ currents requires further elucidation.

Purpose of the Study:

• To characterize the delayed rectifier K+ currents in differentiated human SH-SY5Y neuroblastoma cells.
• To investigate the influence of intracellular sodium (Na+) concentration on K+ current properties.
• To determine the rectification properties and Na+-dependent block of these K+ currents.

Main Methods:

• Tight-seal recording techniques were employed to measure K+ currents.
• Activation and inactivation parameters were assessed.
• Tail current measurements and single-channel recordings were performed.

Main Results:

• A marked rectification of K+ currents was observed at high positive potentials.
• This rectification was dependent on pipette Na+ concentration, absent without Na+ and pronounced with 20-60 mM Na+.
• Internal Na+ caused a fast, voltage-dependent block of K+ currents, with block increasing at more positive potentials.
• Estimated submembrane Na+ concentration in intact cells was approximately 15 mM.

Conclusions:

• Intracellular Na+ acts as a significant modulator of delayed rectifier K+ currents in SH-SY5Y cells.
• The observed rectification and current block are attributed to Na+ interaction with K+ channels.
• These findings highlight the importance of intracellular Na+ homeostasis in regulating neuronal electrical activity.