scholarly journals Interaction of Tetraethylammonium Ion Derivatives with the Potassium Channels of Giant Axons

1971 ◽  
Vol 58 (4) ◽  
pp. 413-437 ◽  
Author(s):  
Clay M. Armstrong
Keyword(s):  
Potassium Conductance ◽  
Squid Axon ◽  
Ammonium Ions ◽  
K Channels ◽  
Fourth Group ◽  
Quaternary Ammonium Ions ◽  
Tetraethylammonium Ion ◽  
K Concentration ◽  
Peak Value ◽  
External K

A number of compounds related to TEA+ (tetraethylammoniumion) were injected into squid axons and their effects on gK (the potassium conductance) were determined. In most of these ions a quaternary nitrogen is surrounded by three ethyl groups and a fourth group that is very hydrophobic. Several of the ions cause inactivation of gK, a type of ionic gating that is not normally seen in squid axon; i.e., after depolarization gK increases and then spontaneously decreases to a small fraction of its peak value even though the depolarization is maintained. Observations on the mechanism of this gating show that (a) QA (quaternary ammonium) ions only enter K+ channels that have open activation gates (the normal permeability gates). (b) The activation gates of QA-occluded channels do not close readily. (c) Hyperpolarization helps to clear QA ions from the channels. (d) Raising the external K+ concentration also helps to clear QA ions from the channels. Observations (c) and (d) strongly suggest that K+ ions traverse the membrane by way of pores, and they cannot be explained by the usual type of carrier model. The data suggest that a K+ pore has two distinct parts: a wide inner mouth that can accept a hydrated K+ ion or a TEA+-like ion, and a narrower portion that can accept a dehydrated or partially dehydrated K+ ion, but not TEA+.

scholarly journals Effects of barium on the potassium conductance of squid axon.

1980 ◽  
Vol 75 (6) ◽  
pp. 727-750 ◽  
Author(s):  
D C Eaton ◽  
M S Brodwick
Keyword(s):  
Rate Constants ◽  
Dissociation Constants ◽  
Divalent Cations ◽  
Potassium Conductance ◽  
Competitive Inhibitor ◽  
Squid Axon ◽  
Voltage Dependent ◽  
Different Temperatures ◽  
Nanomolar Range ◽  
External K

Ba++ ion blocks K+ conductance at concentrations in the nanomolar range. This blockage is time and voltage dependent. From the time dependence it is possible to determine the forward and reverse rate constants for what appears to be an essentially first-order process of Ba++ interaction. The voltage dependence of the rate constants and the dissociation constants place the site of interaction near the middle of the membrane field. Comparison of the efficacy of Ba++ block at various internal K+ concentrations suggests that Ba++ is probably a simple competitive inhibitor of K+ interaction with the K+ conductance. The character of Ba++ block in high external K+ solutions suggests that Ba++ ion may be "knocked-off" the site by inward movement of external K+. Examination of the effects of other divalent cations suggests that the channel may have a closed state with a divalent cation inside the channel. The relative blockage at different temperatures implies a strong interaction between Ba++ and the K+ conductance.

scholarly journals NH2-terminal Inactivation Peptide Binding to C-type–inactivated Kv Channels

2004 ◽  
Vol 123 (5) ◽  
pp. 505-520 ◽  
Author(s):  
Harley T. Kurata ◽  
Zhuren Wang ◽  
David Fedida
Keyword(s):  
Quaternary Ammonium ◽  
Common Mechanism ◽  
Ammonium Ions ◽  
K Channels ◽  
Tail Current ◽  
Current Decay ◽  
Kv Channels ◽  
Quaternary Ammonium Ions ◽  
Recovery From Inactivation ◽  
Before And After

In many voltage-gated K+ channels, N-type inactivation significantly accelerates the onset of C-type inactivation, but effects on recovery from inactivation are small or absent. We have exploited the Na+ permeability of C-type–inactivated K+ channels to characterize a strong interaction between the inactivation peptide of Kv1.4 and the C-type–inactivated state of Kv1.4 and Kv1.5. The presence of the Kv1.4 inactivation peptide results in a slower decay of the Na+ tail currents normally observed through C-type–inactivated channels, an effective blockade of the peak Na+ tail current, and also a delay of the peak tail current. These effects are mimicked by addition of quaternary ammonium ions to the pipette-filling solution. These observations support a common mechanism of action of the inactivation peptide and intracellular quaternary ammonium ions, and also demonstrate that the Kv channel inner vestibule is cytosolically exposed before and after the onset of C-type inactivation. We have also examined the process of N-type inactivation under conditions where C-type inactivation is removed, to compare the interaction of the inactivation peptide with open and C-type–inactivated channels. In C-type–deficient forms of Kv1.4 or Kv1.5 channels, the Kv1.4 inactivation ball behaves like an open channel blocker, and the resultant slowing of deactivation tail currents is considerably weaker than observed in C-type–inactivated channels. We present a kinetic model that duplicates the effects of the inactivation peptide on the slow Na+ tail of C-type–inactivated channels. Stable binding between the inactivation peptide and the C-type–inactivated state results in slower current decay, and a reduction of the Na+ tail current magnitude, due to slower transition of channels through the Na+-permeable states traversed during recovery from inactivation.

scholarly journals Electrical responses to Chemical Stimulation of Squid Olfactory Receptor Cells

1992 ◽  
Vol 162 (1) ◽  
pp. 231-249 ◽  
Author(s):  
MARY T. LUCERO ◽  
FRANK T. HORRIGAN ◽  
WM F. GILLY
Keyword(s):  
Olfactory Receptor ◽  
Action Potentials ◽  
Membrane Conductance ◽  
Ammonium Ions ◽  
Behavioral Experiments ◽  
K Channels ◽  
Olfactory Receptor Cells ◽  
Receptor Cells ◽  
Whole Cell Patch Clamp ◽  
Quaternary Ammonium Ions

Electrical properties of isolated olfactory receptor cells were studied usingb voltage- and current-clamp techniques based on whole-cell patch-clamp methods. Squid olfactory receptor cells contain voltage-gated Na+ and K+ channels and are capable of generating action potentials. Chemicals that elicit escape-jetting responses in behavioral experiments affect the excitability of isolated receptor cells. One set of such chemicals, including quaternary ammonium ions and aminopyridines, blocks K+ channels and increases excitability. Squid ink and L-Dopa also elicit escape jetting, but these substances increase membrane conductance, hyperpolarize the receptor cell and decrease excitability. These experiments indicate that sensory neurons of the olfactory organ are capable of detecting chemical signals and that at least two different transduction mechanismscan lead to similar behavioral responses.

scholarly journals Affinity and Location of an Internal K+ Ion Binding Site in Shaker K Channels

2001 ◽  
Vol 117 (5) ◽  
pp. 373-384 ◽  
Author(s):  
Jill Thompson ◽  
Ted Begenisich
Keyword(s):  
Electric Field ◽  
Binding Sites ◽  
Voltage Dependence ◽  
Ion Binding ◽  
K Channels ◽  
Shaker Channels ◽  
Ion Binding Sites ◽  
K Concentration ◽  
Shaker Potassium Channels ◽  
External K

We have examined the interaction between TEA and K+ ions in the pore of Shaker potassium channels. We found that the ability of external TEA to antagonize block of Shaker channels by internal TEA depended on internal K+ ions. In contrast, this antagonism was independent of external K+ concentrations between 0.2 and 40 mM. The external TEA antagonism of internal TEA block increased linearly with the concentration of internal K+ ions. In addition, block by external TEA was significantly enhanced by increases in the internal K+ concentration. These results suggested that external TEA ions do not directly antagonize internal TEA, but rather promote increased occupancy of an internal K+ site by inhibiting the emptying of that site to the external side of the pore. We found this mechanism to be quantitatively consistent with the results and revealed an intrinsic affinity of the site for K+ ions near 65 mM located ∼7% into the membrane electric field from the internal end of the pore. We also found that the voltage dependence of block by internal TEA was influenced by internal K+ ions. The TEA site (at 0 internal K+) appeared to sense ∼5% of the field from the internal end of the pore (essentially colocalized with the internal K+ site). These results lead to a refined picture of the number and location of ion binding sites at the inner end of the pore in Shaker K channels.

scholarly journals Block of squid axon K channels by internally and externally applied barium ions.

1982 ◽  
Vol 80 (5) ◽  
pp. 663-682 ◽  
Author(s):  
C M Armstrong ◽  
R P Swenson ◽  
S R Taylor
Keyword(s):  
Time Constant ◽  
Recovery Time ◽  
Pulse Voltage ◽  
Squid Axon ◽  
Barium Ions ◽  
K Channels ◽  
Voltage Dependent ◽  
One Step ◽  
Dissociation Constant Kd ◽  
The Way

We have studied the interactions of Ba ion with K channels. Ba2+ blocks these channels when applied either internally or externally in millimolar concentrations. Periodic depolarizations enhance block with internal Ba2+, but diminish the block caused by external Ba2+. At rest, dissociation of Ba2+ from blocked channels is very slow, as ascertained by infrequent test pulses applied after washing Ba2+ form either inside or outside. The time constant for recovery from internal and external Ba2+ is the same. Frequent pulsing greatly shortens recovery time constant after washing away both Ba2+in and Ba2+out. Block by Ba2+ applied internally or externally is voltage dependent. Internal Ba2+ block behaves like a one-step reaction governed by a dissociation constant (Kd) that decreases e-fold/12 mV increase of pulse voltage: block deepens with more positive pulse voltage. For external Ba2+, Kd decreases e-fold/18 mV as holding potential is made more negative: block deepens with increasing negativity. Millimolar external concentrations of some cations can either lessen (K+) or enhance (NH+4, Cs+) block by external Ba2+. NH+4 apparently enhances block by slowing exist of Ba ions from the channels. Rb+ and Cs+ also slow clearing of Ba ions from channels. We think that (a) internally applied Ba2+ moves all the way through the channels, entering only when activation gates are open; (b) externally applied Ba2+ moves two-thirds of the way in, entering predominantly when activation gates are closed; (c) at a given voltage, Ba2+ occupies the same position in the channels whether it entered from inside or outside.

Sign in / Sign up

Export Citation Format

Share Document