Phosphorylation affects voltage gating of the delayed rectifier K+ channel by electrostatic interactions

Area of Science:

• Neuroscience
• Biophysics
• Molecular Biology

Background:

• The delayed rectifier K+ channel in squid axons exhibits altered kinetic and conductive properties upon phosphorylation.
• These changes are linked to shifts in voltage-dependent parameters, suggesting a role for electrostatic interactions.

Purpose of the Study:

• To investigate the electrostatic interactions between the voltage sensor of the K+ channel and phosphate groups.
• To quantify the surface charge density on the cytoplasmic side of the membrane before and after phosphorylation.
• To model the impact of phosphorylation-induced surface potential changes on K+ channel function.

Main Methods:

• Utilized varying intracellular magnesium ion (Mg2+) concentrations to probe surface charge density.
• Measured surface charge density in the absence and presence of ATP (under phosphorylating conditions).
• Developed a kinetic model incorporating surface potential to simulate K+ currents.

Main Results:

• Determined surface charge density values ranging from 1/350 to 1/250 e-/A2 without ATP.
• Found increased surface charge density values between 1/160 and 1/155 e-/A2 under phosphorylating conditions.
• The kinetic model accurately predicted phosphorylation-like changes in K+ currents when incorporating surface potential.

Conclusions:

• Phosphorylation significantly alters the electrostatic environment around the K+ channel voltage sensor.
• Electrostatic interactions are a key mechanism by which phosphorylation modulates voltage-dependent ion channel behavior.
• These findings provide crucial insights into the regulation of neuronal excitability.