Single-channel recording in myelinated nerve fibers reveals one type of Na channel but different K channels.
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.
Jonas
P
P
Physiologisches Institut der Justus-Liebig-Universität, Giessen, Federal Republic of Germany.
Bräu
M E
ME
Hermsteiner
M
M
Vogel
W
W
D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D007700:Kinetics; D008564:Membrane Potentials; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D012584:Sciatic Nerve / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology*; D014982:Xenopus laevis
D015221:Potassium Channels; D015222:Sodium Channels