K channels in excitable cells as multi-ion pores

Hille, Bertil; Schwarz, Wolfgang

doi:10.1016/0361-9230(79)90079-0

Cited by 19 publications

(10 citation statements)

References 26 publications

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“…Punctual measurements with sodium ions were in line with this. The saturation can either be explained by only one ion moving through the channel at a time, or by a number of ions moving through in a single file (20).…”

Section: Discussionmentioning

confidence: 99%

Channelrhodopsin-2 is a leaky proton pump

Feldbauer

Zimmermann

Pintschovius

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

197

182

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Since its discovery, the light-gated cation channel Channelrhodopsin-2 (ChR2) has proven to be a long-sought tool for the noninvasive, light-activated control of neural cells in culture and in living animals. Although ChR2 is widely used in neurobiological applications, little is known about its molecular mechanism. In this work, the unitary conductance of ChR2 was determined for different cations, for example 40 fS at 200 mM NaCl and ؊60 mV, using noise analysis. The kinetics of the ion channel obtained by noise analysis is in excellent agreement with the photocurrent kinetics obtained by voltage-clamp and time-resolved spectroscopy. The inward rectification of the channel could be explained by the single channel parameters. ChR2 represents an ion channel with a 7 transmembrane helix motif, even though the sequence homology of its essential amino acids to those of the light-driven H ؉ pump bacteriorhodopsin (bR) is high. Here, we also show that when ChR2 is expressed in electrofused giant HEK293 cells or reconstituted on planar lipid membranes, it can indeed act as an outwardly driven H ؉ pump, demonstrating that ChR2 is bifunctional, and in-line with other microbial rhodopsins, a H ؉ pump but with a leak that shows ion channel properties.light-driven pump ͉ light-gated channel ͉ noise analysis ͉ ion transport

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Section: Discussionmentioning

confidence: 99%

Channelrhodopsin-2 is a leaky proton pump

Feldbauer

Zimmermann

Pintschovius

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

197

182

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“…In other words, the channel obeys a single-ion occupancy rule for Ba 2+. This makes the physical interpretation of the Ba 2 + blocking phenomena much less equivocal than in the case of the multi-ion blockers [67].…”

Section: Effects Of Tea and Derivativesmentioning

confidence: 99%

“…There are numerous arguments demonstrating that the delayed rectifier is a multi-ion single-file pore [66,67]. The key indications of multiple ion occupancy are the violation of the Ussing flux ratio relation [14], and an effective valence greater than unity for the Cs + blocking reaction [3].…”

Section: Conclusion -A Fanciful Picture Of the Delayed Rectifiermentioning

confidence: 99%

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Conduction and selectivity in potassium channels

1983

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“…(2) mi Hodgkin and Keynes (1955) found n' values near 2.5 for Sepia axons, and in squid axons, n' is between 1.5 and 3.3, depending upon membrane potential and internal potassium concentration (Begenisich and De Weer, 1980). A simple interpretation of these results is that the potassium channel of nerve is a multi-ion pore with three or more binding sites for potassium ions (Heckmann, 1972;Hille and Schwarz, 1979). Although the ionic currents through sodium channels of nerve have been shown not to obey independence criteria, flux-ratio measurements have not been made.…”

Section: Introductionmentioning

confidence: 99%

Sodium flux ratio in voltage-clamped squid giant axons.

Begenisich¹,

Busath²

1981

The Journal of General Physiology

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A B S T a A G T The sodium flux ratio across the axolemma of internally perfused, voltage-clamped giant axons of Loligo pealei has been measured at various membrane potentials. The flux ratio exponent obtained from these measurements was about unity and independent of membrane voltage over the 50 mV range from about -20 to +30 mV. These results, combined with previous measurements of ion permeation through sodium channels, show that the sodium channel behaves like a multi-ion pore with two ion binding sites that are rarely simultaneously occupied by sodium.

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K channels in excitable cells as multi-ion pores

Cited by 19 publications

References 26 publications

Channelrhodopsin-2 is a leaky proton pump

Channelrhodopsin-2 is a leaky proton pump

Conduction and selectivity in potassium channels

Sodium flux ratio in voltage-clamped squid giant axons.

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