Single-channel current/voltage relationships of two kinds of Na+ channel in vertebrate sensory neurons.
The electrical signals of nerve and muscle are fundamentally dependent on the voltage-gated Na+ channel, which is responsible for the rising phase of the action potential. At least two kinds of Na+ channel are expressed in the membrane of frog dorsal root ganglion (DRG) cells: Na+ channels with fast kinetics that are blocked by tetrodotoxin (TTX) at high affinity, and Na+ channels with slower kinetics that are insensitive to TTX. Recordings of single-channel currents from frog DRG cells, under conditions favoring Na+ as the charge carrier, reveal two distinct amplitudes of single-channel events. With 300 mM external Na+, single-channel events that can be measured in the presence of 1 microM TTX have a slope conductance 7.5 pS. In the absence of TTX, events with a slope conductance of 14.9 pS dominate. Ensemble averages of the smaller single-channel events display the slower kinetics characteristic of the macroscopic TTX-insensitive Na+ currents, and ensemble averages of the larger events display the faster kinetics characteristic of the TTX-sensitive currents. The results are consistent with the idea that the toxin-binding site is sufficiently close to the pore to influence ion permeation.
Campbell
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DT
Hatfield Marine Science Center, Oregon State University, Newport 97365-5296.
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D011896:Rana temporaria; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D015222:Sodium Channels; D013779:Tetrodotoxin