Voltage-dependent conductance changes in a nonvoltage-activated sodium current from a mast cell line

Area of Science:

• Cellular Electrophysiology
• Ion Channel Biology
• Molecular Physiology

Background:

• Electrically nonexcitable cells typically lack voltage-activated sodium (Na+) channels.
• Sodium influx in these cells is often mediated by GTP-activated channels, particularly in renal epithelia.
• Previous research identified a novel GTP-dependent Na+ current in rat basophilic leukemia (RBL) cells with distinct characteristics.

Purpose of the Study:

• To investigate the biophysical properties of the GTP-dependent Na+ current in RBL cells.
• To characterize the voltage-dependence and activation mechanisms of this unique Na+ channel.
• To explore the implications of voltage-dependent transitions in a non-voltage-gated channel.

Main Methods:

• Whole-cell patch-clamp technique was employed to record Na+ currents.
• Guanosine triphosphate gamma-S (GTPγS) was used to activate the channels.
• Hyperpolarizing voltage steps and paired pulse protocols were utilized to assess channel behavior.

Main Results:

• Activation by GTPγS evoked transient inward Na+ currents.
• The Na+ current amplitude increased with more positive holding potentials, indicating voltage-dependence.
• Time- and voltage-dependent conductance changes were observed, including outward currents at positive potentials.

Conclusions:

• The identified Na+ channel in RBL cells, though not voltage-activated, exhibits significant voltage-dependent transitions.
• These findings challenge the conventional understanding of ion channel gating in nonexcitable cells.
• The study suggests novel mechanisms underlying voltage dependency in non-voltage-gated ion channels.