Calcium ion as a cofactor in Na channel gating

Area of Science:

• Neuroscience
• Biophysics
• Molecular Biology

Background:

• Voltage-dependent ion channels, including sodium (Na) channels, are crucial for cellular electrical excitability.
• External calcium ions are known to stabilize the resting state of these channels, an effect often attributed to the surface charge hypothesis.
• Calcium ions also exhibit a blocking effect on Na channels, particularly at negative membrane potentials.

Purpose of the Study:

• To investigate the relationship between the gating and blocking effects of calcium ions on voltage-dependent Na channels.
• To propose a unified mechanism explaining both the stabilizing and blocking actions of calcium.

Main Methods:

• Electrophysiological recordings to assess channel gating and block.
• Analysis of the voltage-dependence and kinetics of calcium's effects.
• Comparison of calcium's effects with those of other divalent cations.

Main Results:

• The gating effect (stabilization) and the blocking effect of calcium ions on Na channels are closely correlated.
• Calcium's influence on gating and block is voltage-dependent.
• The observed effects suggest a direct interaction of calcium with the channel pore.

Conclusions:

• Calcium ions act as an essential cofactor in the normal gating of voltage-dependent Na channels.
• Both the stabilizing and blocking effects of calcium arise from its binding within the Na channel.
• The surface charge hypothesis alone does not fully explain calcium's interaction with Na channels.