Modulation of potassium channel gating by external divalent cations

Area of Science:

• Biophysics
• Molecular Biology
• Neuroscience

Background:

• Potassium channels are crucial for cellular electrical signaling.
• The precise mechanisms of ion channel modulation by divalent cations are not fully understood.
• Shaker K channels are a well-characterized model system for studying ion channel function.

Purpose of the Study:

• To investigate the effects of zinc ions (Zn2+) on the gating kinetics of Shaker K channels.
• To elucidate the binding site and mechanism of Zn2+ action on potassium channels.
• To compare the effects of Zn2+ on Shaker K channels with those observed in other potassium channel types.

Main Methods:

• Macroscopic currents of Shaker K channels were recorded in the presence of varying Zn2+ concentrations.
• Single-channel recordings were performed to analyze open channel properties and gating.
• The influence of external pH and chemical modification (TNBS) on Zn2+ effects was assessed.

Main Results:

• Low concentrations of Zn2+ (100 microM) substantially slowed macroscopic activation and inactivation kinetics (approximately three-fold) but minimally affected deactivation.
• Zn2+ effects on activation kinetics were partially reversed by external H+ ions (apparent pK of 7.3).
• Treatment with trinitrobenzene sulfonic acid (TNBS) reduced Zn2+ effects, indicating involvement of amino groups.
• Single-channel studies revealed that Zn2+ delayed the time to first channel opening without altering open channel current or lifetime.

Conclusions:

• Zn2+ ions bind to a specific site on Shaker K channels, modulating gating kinetics.
• The binding site appears to involve amino groups and is sensitive to pH.
• These findings suggest a conserved binding motif for divalent cations across different potassium channel families.
• Zn2+ binding likely slows transitions between closed conformational states of the channel.