Number of water molecules coupled to the transport of sodium, potassium and hydrogen ions via gramicidin, nonactin or valinomycin

Levitt, David G.; Elias, Steven R.; Hautman, Joseph

doi:10.1016/0005-2736(78)90266-3

Cited by 183 publications

(167 citation statements)

References 13 publications

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“…This value is the smallest reported since the first reports for the V stream of the gramicidin channel in 1978 (Levitt et al, 1978;Rosenberg and Finkelstein, 1978). Before discussing the underlying permeation mechanism in our results, we will start by examining the experimental accuracy of the CR w-i values and the validity of the permeation model.…”

Section: Discussionmentioning

confidence: 85%

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Counting Ion and Water Molecules in a Streaming File through the Open-Filter Structure of the K Channel

Iwamoto¹,

Oiki²

2011

J. Neurosci.

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The mechanisms underlying the selective permeation of ions through channel molecules are a fundamental issue related to understanding how neurons exert their functions. The "knock-on" mechanism, in which multiple ions in the selectivity filter are hit by an incoming ion, is one of the leading concepts. This mechanism has been supported by crystallographic studies that demonstrated ion distribution in the structure of the Streptomyces lividans (KcsA) potassium channel. These still pictures under equilibrium conditions, however, do not provide a snapshot of the actual, ongoing permeation processes. To understand the dynamics of permeation, we determined the ratio of the ion and water flow [the water-ion coupling ratio (CR w-i )] through the KcsA channel by measuring the streaming potential (V stream ) electrophysiologically. The V stream value was converted to the CR w-i value, which reveals how individual ion and water molecules are queued in the narrow and short filter during permeation. At high K ϩ concentrations, the CR w-i value was 1.0, indicating that turnover between the alternating ion and water arrays occurs in a single-file manner. At low K ϩ , the CR w-i value was increased to a point over 2.2, suggesting that the filter contained mostly one ion at a time. These average behaviors of permeation were kinetically analyzed for a more detailed understanding of the permeation process. Here, we envisioned the permeation as queues of ion and water molecules and sequential transitions between different patterns of arrays. Under physiological conditions, we predicted that the knock-on mechanism may not be predominant.

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Section: Discussionmentioning

confidence: 85%

“…The following equation relates the slope value to the ratio of the J water and the J ion (the CR w-i ) (Levitt et al, 1978;Rosenberg and Finkelstein, 1978):…”

Section: Evaluation Of the Water-ion Coupling Ratiomentioning

confidence: 99%

Counting Ion and Water Molecules in a Streaming File through the Open-Filter Structure of the K Channel

Iwamoto¹,

Oiki²

2011

J. Neurosci.

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“…Although no detailed molecular picture is available yet explaining how the excess proton is shared among the water molecules [15,16] or how the required transient membrane defects are formed, [17] the unparalleled speed of Grotthuss diffusion is commonly accepted, as it also underlies lateral migration along membrane surfaces [18] and proton hopping through the membrane channels. [19][20][21] Since the exceptional rate of structural diffusion is limited to protons, the question arises as to whether other exceptions to the Meyer-Overton rule may exist and if yes, what the underlying mechanism may be.…”

Section: Protons As An Exception To the Meyer-overton Rulementioning

confidence: 99%

“…These profiles allow calculation of P M,CO2 , since all relevant chemical reactions and diffusion processes can easily be taken into account [Eqs. (19) and (20)]:…”

Section: Gas Transport Through Membranes and Membrane Channelsmentioning

confidence: 99%

110 Years of the Meyer–Overton Rule: Predicting Membrane Permeability of Gases and Other Small Compounds

2009

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The transport of gaseous compounds across biological membranes is essential in all forms of life. Although it was generally accepted that gases freely penetrate the lipid matrix of biological membranes, a number of studies challenged this doctrine as they found biological membranes to have extremely low gas-permeability values. These observations led to the identification of several membrane-embedded "gas" channels, which facilitate the transport of biological active gases, such as carbon dioxide, nitric oxide, and ammonia. However, some of these findings are in contrast to the well-established solubility-diffusion model (also known as the Meyer-Overton rule), which predicts membrane permeabilities from the molecule's oil-water partition coefficient. Herein, we discuss recently reported violations of the Meyer-Overton rule for small molecules, including carboxylic acids and gases, and show that Meyer and Overton continue to rule.

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“…If a membrane containing these channels separates solutions of differing osmolalities, as occurs in distal kidney tubules and the urinary bladder, then an electrical potential difference generated by Na ϩ movement produced from the resultant water flow through the channel will develop. The magnitude of this so-called ''streaming potential'' is related to the number of water molecules contained within the pore region (4)(5)(6)(7).…”

mentioning

confidence: 99%

Streaming potential measurements in αβγ-rat epithelial Na ⁺ channel in planar lipid bilayers

Ismailov

Shlyonsky

Benos

1997

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

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Streaming potentials across cloned epithelial Na ؉ channels (ENaC) incorporated into planar lipid bilayers were measured. We found that the establishment of an osmotic pressure gradient (⌬) across a channel-containing membrane mimicked the activation effects of a hydrostatic pressure differential (⌬P) on ␣␤␥-rENaC, although with a quantitative difference in the magnitude of the driving forces. Moreover, the imposition of a ⌬ negates channel activation by ⌬P when the ⌬ was directed against ⌬P. A streaming potential of 2.0 ؎ 0.7 mV was measured across ␣␤␥-rat ENaC (rENaC)-containing bilayers at 100 mM symmetrical [Na ؉ ] in the presence of a 2 Osmol͞kg sucrose gradient. Assuming single file movement of ions and water within the conduction pathway, we conclude that between two and three water molecules are translocated together with a single Na ؉ ion. A minimal effective pore diameter of 3 Å that could accommodate two water molecules even in single file is in contrast with the 2-Å diameter predicted from the selectivity properties of ␣␤␥-rENaC. The fact that activation of ␣␤␥-rENaC by ⌬P can be reproduced by the imposition of ⌬ suggests that water movement through the channel is also an important determinant of channel activity.Amiloride-sensitive Na ϩ channels found in different epithelia are generally of low-to-moderate conductance and are highly selective for Li ϩ and Na ϩ over the other alkali metal cations (1, 2). These characteristics imply that the conduction region of the pore may be narrow (3). If this is the case, then ions and water should not be able to pass each other, and therefore their flows will be coupled. If a membrane containing these channels separates solutions of differing osmolalities, as occurs in distal kidney tubules and the urinary bladder, then an electrical potential difference generated by Na ϩ movement produced from the resultant water flow through the channel will develop. The magnitude of this so-called ''streaming potential'' is related to the number of water molecules contained within the pore region (4-7).The purpose of the present study was to measure streaming potentials produced by osmotic gradients across planar lipid bilayers containing a recently cloned rat epithelial Na ϩ channel (rENaC). This channel consists of three homologous subunits, termed ␣, ␤, and ␥, that reproduce many of the features of amiloride-sensitive Na ϩ channels found in native epithelia. Moreover, these channels can be activated by a hydrostatic pressure gradient (⌬P) (8-11). In the absence of Ca 2ϩ , these channels can no longer be activated by hydrostatic pressure (10). Consequently, we also tested the hypothesis that water flow through the channel is responsible for activation of ␣␤␥-rENaC following the imposition of ⌬P. Our results indicate that the pore region of ␣␤␥-rENaC can accommodate only two to three water molecules, implying a length of the narrow region of only 0.7-1.0 nm.

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Number of water molecules coupled to the transport of sodium, potassium and hydrogen ions via gramicidin, nonactin or valinomycin

Cited by 183 publications

References 13 publications

Counting Ion and Water Molecules in a Streaming File through the Open-Filter Structure of the K Channel

Counting Ion and Water Molecules in a Streaming File through the Open-Filter Structure of the K Channel

110 Years of the Meyer–Overton Rule: Predicting Membrane Permeability of Gases and Other Small Compounds

Streaming potential measurements in αβγ-rat epithelial Na ⁺ channel in planar lipid bilayers

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Number of water molecules coupled to the transport of sodium, potassium and hydrogen ions via gramicidin, nonactin or valinomycin

Cited by 183 publications

References 13 publications

Counting Ion and Water Molecules in a Streaming File through the Open-Filter Structure of the K Channel

Counting Ion and Water Molecules in a Streaming File through the Open-Filter Structure of the K Channel

110 Years of the Meyer–Overton Rule: Predicting Membrane Permeability of Gases and Other Small Compounds

Streaming potential measurements in αβγ-rat epithelial Na + channel in planar lipid bilayers

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Streaming potential measurements in αβγ-rat epithelial Na ⁺ channel in planar lipid bilayers