scholarly journals Gating-dependent mechanism of 4-aminopyridine block in two related potassium channels.

1993 ◽  
Vol 102 (5) ◽  
pp. 797-816 ◽  
Author(s):  
G E Kirsch ◽  
J A Drewe
Keyword(s):  
Single Channel ◽  
K Channels ◽  
Voltage Gated ◽  
Gating Mechanism ◽  
Excitable Membranes ◽  
Single Channel Analysis ◽  
Channel Analysis ◽  
A Site ◽  
Selective Blocker ◽  
K Currents

4-aminopyridine (4AP) is widely used as a selective blocker of voltage-activated K+ currents in excitable membranes, but its mechanism and site of action at the molecular level are not well understood. To address this problem we have analyzed 4AP block in Kv2.1 and Kv3.1, mammalian representatives of the Drosophila Shab and Shaw subfamilies of voltage-gated K+ channels, respectively. The two channels were expressed in Xenopus oocytes and analyzed at both the macroscopic and single channel levels. Whole cell analysis showed that 4AP sensitivity of Kv3.1 was approximately 150 times greater than that of Kv2.1. Patch clamp analysis revealed that the mechanism of 4AP block in both channels was qualitatively similar. 4AP reached its blocking site via the cytoplasmic side of the channels, the ON rate for block was strongly accelerated when channels opened and the drug was trapped in closed channels. Single channel analysis showed that 4AP decreased burst duration and increased the latency-to-first-opening. These effects were found to be related, respectively to drug ON and OFF rates in the activated channel. Kv3.1's high 4AP sensitivity relative to Kv2.1 was associated with both a slower OFF rate and therefore increased stability of the blocked state, as well as a faster ON rate and therefore increased access to the binding site. Our results indicate that in both channels 4AP enters the intracellular mouth to bind to a site that is guarded by the gating mechanism. Differences in channel gating as well as differences in the structure of the intracellular mouth may be important for specifying the 4AP sensitivity in related voltage-gated K+ channels.

Hippocampal hypoglycaemia-activated K+ channels: single-channel analysis of glucose and voltage dependence

1994 ◽  
Vol 429 (1) ◽  
pp. 58-63 ◽  
Author(s):  
Cinzia Tromba ◽  
Antonino Salvaggio ◽  
Giorgio Racagni ◽  
Andrea Volterra
Keyword(s):  
Voltage Dependence ◽  
Single Channel ◽  
K Channels ◽  
Single Channel Analysis ◽  
Channel Analysis

scholarly journals Voltage-gated potassium channels in brown fat cells.

1989 ◽  
Vol 93 (3) ◽  
pp. 451-472 ◽  
Author(s):  
M T Lucero ◽  
P A Pappone
Keyword(s):  
Single Channel ◽  
Reversal Potential ◽  
Brown Fat ◽  
Membrane Currents ◽  
Delayed Rectifier ◽  
Fat Cells ◽  
K Channels ◽  
Voltage Gated ◽  
K Currents ◽  
External K

We studied the membrane currents of isolated cultured brown fat cells from neonatal rats using whole-cell and single-channel voltage-clamp recording. All brown fat cells that were recorded from had voltage-gated K currents as their predominant membrane current. No inward currents were seen in these experiments. The K currents of brown fat cells resemble the delayed rectifier currents of nerve and muscle cells. The channels were highly selective for K+, showing a 58-mV change in reversal potential for a 10-fold change in the external [K+]. Their selectivity was typical for K channels, with relative permeabilities of K+ greater than Rb+ greater than NH+4 much greater than Cs+, Na+. The K currents in brown adipocytes activated with a sigmoidal delay after depolarizations to membrane potentials positive to -50 mV. Activation was half maximal at a potential of -28 mV and did not require the presence of significant concentrations of internal calcium. Maximal voltage-activated K conductance averaged 20 nS in high external K+ solutions. The K currents inactivated slowly with sustained depolarization with time constants for the inactivation process on the order of hundreds of milliseconds to tens of seconds. The K channels had an average single-channel conductance of 9 pS and a channel density of approximately 1,000 channels/cell. The K current was blocked by tetraethylammonium or 4-aminopyridine with half maximal block occurring at concentrations of 1-2 mM for either blocker. K currents were unaffected by two blockers of Ca2+-activated K channels, charybdotoxin and apamin. Bath-applied norepinephrine did not affect the K currents or other membrane currents under our experimental conditions. These properties of the K channels indicate that they could produce an increase in the K+ permeability of the brown fat cell membrane during the depolarization that accompanies norepinephrine-stimulated thermogenesis, but that they do not contribute directly to the norepinephrine-induced depolarization.

Single-channel analysis of a large conductance channel in peroxisomes from rat liver

1989 ◽  
Vol 984 (3) ◽  
pp. 351-359 ◽  
Author(s):  
Marc Lemmens ◽  
Kristine Verheyden ◽  
Paul Van Veldhoven ◽  
Johan Vereecke ◽  
Guy P. Mannaerts ◽  
...  
Keyword(s):  
Rat Liver ◽  
Single Channel ◽  
Single Channel Analysis ◽  
Large Conductance Channel ◽  
Channel Analysis
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