Single-Channel Recording in Myelinated Nerve Fibers Reveals One Type of Na Channel but Different K Channels

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 86; no. 18; pp. 7238 - 7242
• Main Authors: Jonas, Peter, Bräu, Michael E., Hermsteiner, Markus, Vogel, Werner
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01.09.1989; National Acad Sciences
• Subjects: Animals; Axons; Axons - physiology; Axons - ultrastructure; Biological and medical sciences; Cell physiology; Electric current; Fundamental and applied biological sciences. Psychology; Kinetics; Membrane potential; Membrane Potentials; Molecular and cellular biology; Myelinated nerve fibers; Nerve Fibers, Myelinated - physiology; Neurotransmission; P branes; Pharmacology; Pipettes; Potassium Channels - physiology; Sciatic Nerve - physiology; Sodium Channels - physiology; Toxins; Xenopus laevis; Myelin; Xenopus laevis; Amphibia; Electrophysiology; Myelinated nerve fiber; Patch clamp method; Nervous system; Salientia; Ionic channel; Characterization; Vertebrata; Sodium; Node of Ranvier; Electrical conductance; Membrane potential; Pharmacokinetics; Potassium
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.86.18.7238

Amphibian myelinated nerve fibers were treated with collagenase and protease. Axons with retraction of the myelin sheath were patch-clamped in the nodal and paranodal region. One type of Na channel was found. It has a single-channel conductance of 11 pS (15 degrees C) and is blocked by tetrodotoxin. Averaged events show the typical activation and inactivation kinetics of macroscopic Na current. Three potential-dependent K channels were identified (I, F, and S channel). The I channel, being the most frequent type, has a single-channel conductance of 23 pS (inward current, 105 mM K on both sides of the membrane), activates between -60 and -30 mV, deactivates with intermediate kinetics, and is sensitive to dendrotoxin. The F channel has a conductance of 30 pS, activates between -40 and 60 mV, and deactivates with fast kinetics. The former inactivates within tens of seconds; the latter inactivates within seconds. The third type, the S channel, has a conductance of 7 pS and deactivates slowly. All three channels can be blocked by external tetraethylammonium chloride. We suggest that these distinct K channel types form the basis for the different components of macroscopic K current described previously.