Single voltage-dependent potassium channels in rat peripheral nerve membrane
1. Voltage-dependent potassium channels were investigated in rat axonal membrane by means of the patch-clamp recording technique. Three different types of channels (F, I and S) have been characterized on the basis of their single-channel conductance, activation, deactivation and inactivation propert...
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Published in | The Journal of physiology Vol. 460; no. 1; pp. 675 - 691 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Oxford
The Physiological Society
01.01.1993
Blackwell |
Subjects | |
Online Access | Get full text |
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Summary: | 1. Voltage-dependent potassium channels were investigated in rat axonal membrane by means of the patch-clamp recording technique.
Three different types of channels (F, I and S) have been characterized on the basis of their single-channel conductance, activation,
deactivation and inactivation properties. 2. The fast (F) channels were activated smoothly at potentials (E) between -50 and
50 mV (E50 = 4.6 mV). They had a conductance of 55 pS for inward current and 30 pS for outward current in solutions containing
155 mM K+ (high K+) on both sides of the membrane at 21-23 degrees C. The F-channels demonstrated the fastest deactivation,
within 1-2 ms, and inactivated in a few hundreds of milliseconds. The time constant of inactivation was 143 ms at E = +40
mV. 3. The intermediate (I) channels activated steeply between E = -70 and -50 mV (E50 = -64.2 mv) and had a single-channel
conductance of 33 pS for inward and 18 ps for outward currents. The I-channels deactivated with intermediate kinetics with
the time constants of 20.4 ms and 10.1 ms at E = -80 mV and E = -100 mV, respectively. Complete inactivation of the channels
developed over tens of seconds. The time constant of inactivation was 7.4 s at E = +40 mV. 4. The slow (S) channels were active
at potentials positive to -90 mV. Their conductance was 10 pS for inward currents. The time constant of activation of the
S-channels was strongly potential dependent. At a holding potential of -100 mV the channels deactivated during a long time
interval between 30 ms and 1 s, producing long-lasting tail currents. The mean time constant of deactivation for S-channels
was 129 ms. 5. The conductances of F- and I-channels measured under normal physiological conditions (Ringer solution in bath)
were 17 and 10 pS, respectively. 6. Tetraethylammonium (TEA), the classic blocker of potassium channels, suppressed F-, I-
and S-channels. It gradually reduced the apparent amplitude of unitary currents in a dose-dependent manner with IC50 equal
to 1.2 mM for F-channels, 0.6 mM for I-channels and 1.4 mM for S-channels. Dendrotoxin (DTX), a toxin from the green mamba
snake, considerably inhibited the I tail currents at nanomolar concentrations (IC50 = 2.8 nM) while the amplitudes of single
I-channel currents were not affected. 7. The K+ channels of F, I and S types form the basis of the potassium conductivity
in mammalian peripheral myelinated axon. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.1993.sp019493 |