A quantitative description of membrane currents in rabbit myelinated nerve

Area of Science:

• Neuroscience
• Biophysics
• Mammalian Physiology

Background:

• Voltage-clamp studies are crucial for understanding ion channel kinetics in excitable cells.
• Myelinated nerve fibers, particularly the nodes of Ranvier, are key sites for action potential propagation.

Purpose of the Study:

• To investigate the ionic currents and voltage-dependent properties of sodium channels in rabbit nodes of Ranvier.
• To compare the electrophysiological characteristics of rabbit nodes with those of frog nodes.
• To reconstruct the action potential of rabbit myelinated nerve fibers based on measured ionic currents.

Main Methods:

• Single rabbit myelinated nerve fibers were studied using voltage-clamp techniques at 14°C.
• A novel calibration method was developed using internodal resistance measurements.
• Ionic currents were resolved into sodium and leak components; potassium currents were found to be negligible.

Main Results:

• Rabbit sodium currents were accurately modeled using Hodgkin-Huxley kinetics (m²h).
• Key differences were observed in sodium current kinetics: faster inactivation (τh) and a hyperpolarized P(Na)(E) curve in rabbits compared to frogs.
• The reconstructed rabbit action potential, driven by sodium influx and leak currents, closely matched experimental recordings.

Conclusions:

• Mammalian (rabbit) sodium channel kinetics differ significantly from amphibian (frog) counterparts, particularly in inactivation speed and voltage dependence.
• The reconstructed action potential accurately reflects the contribution of sodium and leak currents to depolarization and repolarization in rabbit nerve fibers.
• Despite kinetic differences, maximal sodium conductance (gNa) is comparable between similarly sized frog and rabbit nodes at 14°C.