scholarly journals Discrete Ba2+ block as a probe of ion occupancy and pore structure in the high-conductance Ca2+ -activated K+ channel.

1988 ◽  
Vol 92 (5) ◽  
pp. 569-586 ◽  
Author(s):  
J Neyton ◽  
C Miller
Keyword(s):  
External Solution ◽  
K Channel ◽  
Enhancement Effect ◽  
Single Channels ◽  
Internal Solution ◽  
Conduction Pathway ◽  
Lock In Effect ◽  
Lock In ◽  
High Conductance ◽  
External K

In this study, high-conductance Ca2+-activated K+ channels from rat skeletal muscle were incorporated into planar phospholipid bilayers, and discrete blockade of single channels by Ba2+ was studied. With 150 mM K+ held constant in the internal solution, increasing external K+ over the range 100-1,000 mM raises the rate of Ba2+ dissociation. This "enhancement effect," which operates at K+ concentrations 3-4 orders of magnitude higher than those required for the "lockin" effect described previously, depends on applied voltage, saturates with K+ concentration, and is not observed with Na+. The voltage dependence of the Ba2+ off-rate varies with external K+ in a way suggesting that K+, entering the channel from the external side, forces Ba2+ dissociation to the internal solution. With K+ held fixed in the external solution, the Ba2+ off-rate decreases as internal K+ is raised over the range 0-50 mM. This "lock-in" effect is similar to that seen on the external side (Neyton and Miller, 1988), except that the internal lock-in site is of lower affinity and shows only a fivefold preference for K+ over Na+. All the results taken together argue strongly that this channel's conduction pathway contains four sites of very high affinity for K+, all of which may be simultaneously occupied under normal conducting conditions. According to this view, the mutual destabilization resulting from this high ionic occupancy leads to the unusually high conductance of this K+-specific channel.

scholarly journals Mechanism of charybdotoxin block of the high-conductance, Ca2+-activated K+ channel.

1988 ◽  
Vol 91 (3) ◽  
pp. 335-349 ◽  
Author(s):  
R MacKinnon ◽  
C Miller
Keyword(s):  
Lipid Bilayers ◽  
External Solution ◽  
Dissociation Rate ◽  
K Channel ◽  
Internal Solution ◽  
Conduction Pathway ◽  
Voltage Dependent ◽  
K Concentration ◽  
A Site ◽  
Low K

The mechanism of charybdotoxin (CTX) block of single Ca2+-activated K+ channels from rat muscle was studied in planar lipid bilayers. CTX blocks the channel from the external solution, and K+ in the internal solution specifically relieves toxin block. The effect of K+ is due solely to an enhancement of the CTX dissociation rate. As internal K+ is raised, the CTX dissociation rate increases in a rectangular hyperbolic fashion from a minimum value at low K+ of 0.01 s-1 to a maximum value of approximately 0.2 s-1. As the membrane is depolarized, internal K+ more effectively accelerates CTX dissociation. As the membrane is hyperpolarized, the toxin dissociation rate approaches 0.01 s-1, regardless of the K+ concentration. When internal K+ is replaced by Na+, CTX dissociation is no longer voltage dependent. The permeant ion Rb also accelerates toxin dissociation from the internal solution, while the impermeant ions Li, Na, Cs, and arginine do not. These results argue that K ions can enter the CTX-blocked channel from the internal solution to reach a site located nearly all the way through the conduction pathway; when K+ occupies this site, CTX is destabilized on its blocking site by approximately 1.8 kcal/mol. The most natural way to accommodate these conclusions is to assume that CTX physically plugs the channel's externally facing mouth.

scholarly journals Coupling of voltage-dependent gating and Ba++ block in the high-conductance, Ca++-activated K+ channel.

1987 ◽  
Vol 90 (3) ◽  
pp. 427-449 ◽  
Author(s):  
C Miller ◽  
R Latorre ◽  
I Reisin
Keyword(s):  
Lipid Bilayers ◽  
Dissociation Rate ◽  
K Channel ◽  
Single Channels ◽  
Closed Channel ◽  
Association Rate ◽  
Conduction Pathway ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
High Conductance

Voltage-dependent Ca++-activated K+ channels from rat skeletal muscle were reconstituted into planar lipid bilayers, and the kinetics of block of single channels by Ba++ were studied. The Ba++ association rate varies linearly with the probability of the channel being open, while the dissociation rate follows a rectangular hyperbolic relationship with open-state probability. Ba ions can be occluded within the channel by closing the channel with a strongly hyperpolarizing voltage applied during a Ba++-blocked interval. Occluded Ba ions cannot dissociate from the blocking site until after the channel opens. The ability of the closed channel to occlude Ba++ is used as an assay to study the channel's gating equilibrium in the blocked state. The blocked channel opens and closes in a voltage-dependent process similar to that of the unblocked channel. The presence of a Ba ion destabilizes the closed state of the blocked channel, however, by 1.5 kcal/mol. The results confirm that Ba ions block this channel by binding in the K+-conduction pathway. They further show that the blocking site is inaccessible to Ba++ from both the cytoplasmic and external solutions when the channel is closed.

scholarly journals A conductance maximum observed in an inward-rectifier potassium channel.

1994 ◽  
Vol 104 (3) ◽  
pp. 477-486 ◽  
Author(s):  
Z Lu ◽  
R MacKinnon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Inward Rectifier ◽  
Ion Concentration ◽  
K Channel ◽  
Single Channels ◽  
Ligand Interaction ◽  
Membrane Biology ◽  
Maximum Value ◽  
Conduction Pathway

One prediction of a multi-ion pore is that its conductance should reach a maximum and then begin to decrease as the concentration of permeant ion is raised equally on both sides of the membrane. A conductance maximum has been observed at the single-channel level in gramicidin and in a Ca(2+)-activated K+ channel at extremely high ion concentration (> 1,000 mM) (Hladky, S. B., and D. A. Haydon. 1972. Biochimica et Biophysica Acta. 274:294-312; Eisenmam, G., J. Sandblom, and E. Neher. 1977. In Metal Ligand Interaction in Organic Chemistry and Biochemistry. 1-36; Finkelstein, P., and O. S. Andersen. 1981. Journal of Membrane Biology. 59:155-171; Villarroel, A., O. Alvarez, and G. Eisenman. 1988. Biophysical Journal. 53:259a. [Abstr.]). In the present study we examine the conductance-concentration relationship in an inward-rectifier K+ channel, ROMK1. Single channels, expressed in Xenopus oocytes, were studied using inside-out patch recording in the absence of internal Mg2+ to eliminate blockade of outward current. Potassium, at equal concentrations on both sides of the membrane, was varied from 10 to 1,000 mM. As K+ was raised from 10 mM, the conductance increased steeply and reached a maximum value (39 pS) at 300 mM. The single-channel conductance then became progressively smaller as K+ was raised beyond 300 mM. At 1000 mM K+, the conductance was reduced to approximately 75% of its maximum value. The shape of the conductance-concentration curve observed in the ROMK1 channel implies that it has multiple K(+)-occupied binding sites in its conduction pathway.

scholarly journals A computational study of barium blockades in the KcsA potassium channel based on multi-ion potential of mean force calculations and free energy perturbation

2013 ◽  
Vol 142 (4) ◽  
pp. 451-463 ◽  
Author(s):  
Christopher N. Rowley ◽  
Benoît Roux
Keyword(s):  
Free Energy ◽  
Computational Study ◽  
Potential Of Mean Force ◽  
Free Energy Perturbation ◽  
K Channel ◽  
Rate Theory ◽  
Crystallographic Structure ◽  
Energy Perturbation ◽  
Lock In Effect ◽  
Lock In

Electrophysiological studies have established that the permeation of Ba2+ ions through the KcsA K+-channel is impeded by the presence of K+ ions in the external solution, while no effect is observed for external Na+ ions. This Ba2+ “lock-in” effect suggests that at least one of the external binding sites of the KcsA channel is thermodynamically selective for K+. We used molecular dynamics simulations to interpret these lock-in experiments in the context of the crystallographic structure of KcsA. Assuming that the Ba2+ is bound in site S2 in the dominant blocked state, we examine the conditions that could impede its translocation and cause the observed “lock-in” effect. Although the binding of a K+ ion to site S1 when site S2 is occupied by Ba2+ is prohibitively high in energy (>10 kcal/mol), binding to site S0 appears to be more plausible (ΔG > 4 kcal/mol). The 2D potential of mean force (PMF) for the simultaneous translocation of Ba2+ from site S2 to site S1 and of a K+ ion on the extracellular side shows a barrier that is consistent with the concept of external lock-in. The barrier opposing the movement of Ba2+ is very high when a cation is in site S0, and considerably smaller when the site is unoccupied. Furthermore, free energy perturbation calculations show that site S0 is selective for K+ by 1.8 kcal/mol when S2 is occupied by Ba2+. However, the same site S0 is nonselective when site S2 is occupied by K+, which shows that the presence of Ba2+ affects the selectivity of the pore. A theoretical framework within classical rate theory is presented to incorporate the concentration dependence of the external ions on the lock-in effect.

The Capital Gains Lock-In Effect and Earnings Quality

2019 ◽  
Author(s):  
Stephen G. Dimmock ◽  
Fan Feng ◽  
Huai Zhang
Keyword(s):  
Earnings Quality ◽  
Capital Gains ◽  
Lock In Effect ◽  
Lock In

scholarly journals Informal Reform of the United Nations Security Council

2018 ◽  
Vol 40 (1) ◽  
pp. 97-115
Author(s):  
Mariana Pimenta Oliveira Baccarini
Keyword(s):  
Cold War ◽  
United Nations ◽  
Security Council ◽  
United Nations Security Council ◽  
Decision Making Process ◽  
Institutional Perspective ◽  
The United Nations ◽  
Lock In Effect ◽  
The Cold War ◽  
Lock In

Abstract This article analyses attempts to reform the United Nations Security Council from a historical-institutional perspective. It argues that the possibilities for reform have suffered from a ‘lock-in’ effect that has rendered the UN resistant to change. On the other hand, the UN decision-making process has evolved since its establishment, especially since the end of the Cold War, in response to new power aspirations, making it more representative and legitimate. The Security Council has also undergone continuous informal reform that has allowed it to adapt to new times.

Complaint behaviour in multichannel retailing: a cross-stage approach

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Marta Frasquet ◽  
Marco Ieva ◽  
Cristina Ziliani
Keyword(s):  
Online Survey ◽  
Latent Class ◽  
Service Failure ◽  
Service Recovery ◽  
Content Type ◽  
Multichannel Retailing ◽  
Synergy Effects ◽  
Lock In Effect ◽  
Lock In ◽  
Post Purchase

PurposeThis paper analyses how the purchase channel and customer complaint goals affect the sequential choice of post–purchase complaint channels when customers experience a service failure followed by a service recovery failure (double deviation).Design/methodology/approachAn online survey involving a scenario manipulation was conducted with 577 apparel shoppers. The study employs multi-group latent class analysis to estimate latent customer segments within both online and offline groups of shoppers and compare latent classes between the two groups.FindingsThe results show that the purchase channel has a lock-in effect on the complaint channel, which is stronger for offline buyers. Moreover, there is evidence of channel synergy effects in the case of having to complain twice: shoppers who complain in store in the first attempt turn to online channels in the second complaint attempt, and vice versa. Complaint goals shape the choice of complaint channels and define different shopper segments.Originality/valueThe present study is the first to adopt a cross-stage approach that analyses the dependencies between the purchase channel and the complaint channel used on two subsequent occasions: the first complaint after a service failure and the second following a service recovery failure.

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