Conductance stability and Na+ interaction with Shab K+ channels under low K+ conditions

There have been periodic reports of nonclassic (4-aminopyridine insensitive) transient outward K+ current in guinea pig ventricular myocytes, with the most recent one describing a novel voltage-gated inwardly rectifying type. In the present study, we have investigated a transient outward current that overlaps inward Ca2+ current ( ICa,L) in myocytes dialyzed with 10 mM K+ solution and superfused with Tyrode’s solution. Although depolarizations from holding potential ( Vhp) −40 to 0 mV elicited relatively small inward ICa,L in these myocytes, removal of external K+ or addition of 0.2 mM Ba2+ more than doubled the amplitude of the current. The basis of the enhancement of ICa,L was the suppression of a large transient outward K+ current. Similar enhancement was observed when Vhp was moved to −80 mV and test depolarizations were preceded by short prepulses to −40 mV. Investigation of the time and voltage properties of the outward K+ transient indicated that it was inwardly rectifying and unlikely to be carried by voltage-gated channels. The outward transient was attenuated in myocytes dialyzed with high-Mg2+ solution, accelerated in myocytes dialyzed with 100 μM spermine solution, and abolished with time in myocytes dialyzed with ATP-free solution. These and other findings suggest that the outward transient is a component of classic “time-independent” inwardly rectifying K+ current.

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Two Stable, Conducting Conformations of the Selectivity Filter in Shaker K+ Channels

The Journal of General Physiology ◽

10.1085/jgp.200509251 ◽

2005 ◽

Vol 125 (6) ◽

pp. 619-629 ◽

Cited By ~ 7

Author(s):

Jill Thompson ◽

Ted Begenisich

Keyword(s):

Voltage Dependence ◽

Relative Proportion ◽

Selectivity Filter ◽

K Channel ◽

K Channels ◽

High Affinity ◽

K Concentration ◽

The One ◽

Low K ◽

Two Populations

We have examined the voltage dependence of external TEA block of Shaker K+ channels over a range of internal K+ concentrations from 2 to 135 mM. We found that the concentration dependence of external TEA block in low internal K+ solutions could not be described by a single TEA binding affinity. The deviation from a single TEA binding isotherm was increased at more depolarized membrane voltages. The data were well described by a two-component binding scheme representing two, relatively stable populations of conducting channels that differ in their affinity for external TEA. The relative proportion of these two populations was not much affected by membrane voltage but did depend on the internal K+ concentration. Low internal K+ promoted an increase in the fraction of channels with a low TEA affinity. The voltage dependence of the apparent high-affinity TEA binding constant depended on the internal K+ concentration, becoming almost voltage independent in 5 mM. The K+ sensitivity of these low- and high-affinity TEA states suggests that they may represent one- and two-ion occupancy states of the selectivity filter, consistent with recent crystallographic results from the bacterial KcsA K+ channel. We therefore analyzed these data in terms of such a model and found a large (almost 14-fold) difference between the intrinsic TEA affinity of the one-ion and two-ion modes. According to this analysis, the single ion in the one-ion mode (at 0 mV) prefers the inner end of the selectivity filter twofold more than the outer end. This distribution does not change with internal K+. The two ions in the two-ion mode prefer to occupy the inner end of the selectivity filter at low K+, but high internal K+ promotes increased occupancy of the outer sites. Our analysis further suggests that the four K+ sites in the selectivity filter are spaced between 20 and 25% of the membrane electric field.

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Inhibitor of growth 4 (ING4) is up-regulated by a low K intake and suppresses renal outer medullary K channels (ROMK) by MAPK stimulation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.0703383104 ◽

2007 ◽

Vol 104 (22) ◽

pp. 9517-9522 ◽

Cited By ~ 6

Author(s):

X. Zhang ◽

D.-H. Lin ◽

Y. Jin ◽

K.-S. Wang ◽

Y. Zhang ◽

...

Keyword(s):

K Channels ◽

Low K

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Faculty Opinions recommendation of Inhibitor of growth 4 (ING4) is up-regulated by a low K intake and suppresses renal outer medullary K channels (ROMK) by MAPK stimulation.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1087824.540751 ◽

2007 ◽

Author(s):

William Welch

Keyword(s):

K Channels ◽

Low K

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Na+ Interaction with the Pore of Shaker B K+ Channels

The Journal of General Physiology ◽

10.1085/jgp.118.6.639 ◽

2001 ◽

Vol 118 (6) ◽

pp. 639-648 ◽

Cited By ~ 9

Author(s):

Froylán Gómez-Lagunas

Keyword(s):

Molar Fraction ◽

K Channels ◽

Na Ions ◽

The Stability ◽

A Site ◽

Low K ◽

External K

The Shaker B K+ conductance (GK) collapses (in a reversible manner) if the membrane is depolarized and then repolarized in, 0 K+, Na+-containing solutions (Gómez-Lagunas, F. 1997. J. Physiol. 499:3–15; Gómez-Lagunas, F. 1999. Biophys. J. 77:2988–2998). In this work, the role of Na+ ions in the collapse of GK in 0-K+ solutions, and in the behavior of the channels in low K+, was studied. The main findings are as follows. First, in 0-K+ solutions, the presence of Na+ ions is an important factor that speeds the collapse of GK. Second, external Na+ fosters the drop of GK by binding to a site with a Kd = 3.3 mM. External K+ competes, in a mutually exclusive manner, with Nao+ for binding to this site, with an estimated Kd = 80 μM. Third, NMG and choline are relatively inert regarding the stability of GK; fourth, with [Ko+] = 0, the energy required to relieve Nai+ block of Shaker (French, R.J., and J.B. Wells. 1977. J. Gen. Physiol. 70:707–724; Starkus, J.G., L. Kuschel, M. Rayner, and S. Heinemann. 2000. J. Gen. Physiol. 110:539–550) decreases with the molar fraction of Nai+ (XNa,i), in an extent not accounted for by the change in ΔμNa. Finally, when XNa,i = 1, GK collapses by the binding of Nai+ to two sites, with apparent Kds of 2 and 14.3 mM.

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Electron Probe Analysis of Vertebrate Smooth Muscle: Distribution of Ca and Ci

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100091652 ◽

1976 ◽

Vol 34 ◽

pp. 334-335 ◽

Cited By ~ 1

Author(s):

Avril V. Somlyo ◽

H. Shuman ◽

A.P. Somlyo

Keyword(s):

Smooth Muscle ◽

Electron Probe ◽

Preliminary Report ◽

Cell Damage ◽

Electron Probe Analysis ◽

Perinuclear Space ◽

Probe Analysis ◽

High K ◽

Low K ◽

Initial Results

This is a preliminary report of electron probe analysis of rabbit portal-anterior mesenteric vein (PAMV) smooth muscle cryosectioned without fixation or cryoprotection. The instrumentation and method of electron probe quantitation used (1) and our initial results with cardiac (2) and skeletal (3) muscle have been presented elsewhere.In preparations depolarized with high K (K2SO4) solution, significant calcium peaks were detected over the sarcoplasmic reticulum (Fig 1 and 2) and the continuous perinuclear space. In some of the fibers there were also significant (up to 200 mM/kg dry wt) calcium peaks over the mitochondria. However, in smooth muscle that was not depolarized, high mitochondrial Ca was found in fibers that also contained elevated Na and low K (Fig 3). Therefore, the possibility that these Ca-loaded mitochondria are indicative of cell damage remains to be ruled out.

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