Large Diameter of Palytoxin-induced Na/K Pump Channels and Modulation of Palytoxin Interaction by Na/K Pump Ligands

Palytoxin binds to Na/K pumps to generate nonselective cation channels whose pore likely comprises at least part of the pump's ion translocation pathway. We systematically analyzed palytoxin's interactions with native human Na/K pumps in outside-out patches from HEK293 cells over a broad range of ionic and nucleotide conditions, and with or without cardiotonic steroids. With 5 mM internal (pipette) [MgATP], palytoxin activated the conductance with an apparent affinity that was highest for Na+-containing (K+-free) external and internal solutions, lowest for K+-containing (Na+-free) external and internal solutions, and intermediate for the mixed external Na+/internal K+, and external K+/internal Na+ conditions; with Na+ solutions and MgATP, the mean dwell time of palytoxin on the Na/K pump was about one day. With Na+ solutions, the apparent affinity for palytoxin action was low after equilibration of patches with nucleotide-free pipette solution. That apparent affinity was increased in two phases as the equilibrating [MgATP] was raised over the submicromolar, and submillimolar, ranges, but was increased by pipette MgAMPPNP in a single phase, over the submillimolar range; the apparent affinity at saturating [MgAMPPNP] remained ∼30-fold lower than at saturating [MgATP]. After palytoxin washout, the conductance decay that reflects palytoxin unbinding was accelerated by cardiotonic steroid. When Na/K pumps were preincubated with cardiotonic steroid, subsequent activation of palytoxin-induced conductance was greatly slowed, even after washout of the cardiotonic steroid, but activation could still be accelerated by increasing palytoxin concentration. These results indicate that palytoxin and a cardiotonic steroid can simultaneously occupy the same Na/K pump, each destabilizing the other. The palytoxin-induced channels were permeable to several large organic cations, including N-methyl-d-glucamine+, suggesting that the narrowest section of the pore must be ∼7.5 Å wide. Enhanced understanding of palytoxin action now allows its use for examining the structures and mechanisms of the gates that occlude/deocclude transported ions during the normal Na/K pump cycle

Directional cue and landmark configurations: The effect of rotating one set of landmarks relative to another

This is the author accepted manuscript. The final version is available from the American Psychological Association via the DOI in this recordIn this article we addressed the question whether rats can use distal landmarks as directional cues that are used in combination with other proximal landmark configurations. The animals were trained with an A, B, C, and D landmark configuration in the Morris pool, where B and C are the near (to platform) landmarks and A and D the far ones. We also added another more distal "directional" cue Z (a white strip attached to the black curtain surrounding the pool). Experiment 1 shows a robust detrimental effect on the time spent by the rats swimming in the platform quadrant when the location of all landmarks was "Inverted" (rotated by 180 degrees) with respect to Z. A similar detrimental effect was found when, after the inversion manipulation, the locations of the near and far landmarks were "Flipped" (B swapped with C and A with D). Rats in both Inverted and Flipped tests spent more time in the Z quadrant compared to the platform quadrant (BC). Experiment 1b provided evidence distinguishing between alternative explanations of how the directional cue Z acts in combination with the other landmarks. The results from both experiments show that Z operates differently to the standard landmarks. It can function as a beacon in its own right. It can also combine with the other landmarks to produce a high level of search performance, in a way that we hypothesize to be distinct from that described by the configural analysis often applied to multiple landmarks.European Union Horizon 2020Economic and Social Research Council (ESRC

Calorimetric and acoustic study of binary mixtures containing an isomeric chlorobutane and butyl ethyl ether or methyl tert-butyl ether

Densities and speeds of sound in the temperature range 283.15-313.15 K have been measured for the binary mixtures formed by an isomeric chlorobutane (1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, or 2-chloro-2-methylpropane) and butyl ethyl ether or methyl tert-butyl ether. Excess isentropic compressibilities were calculated from the experimental data. Excess enthalpies at T = 298.15 K are also included for the same binary mixtures. All these properties provide an insight into the nature of interactions operating on the present systems. Finally, the Prigogine-Flory-Patterson theory has been used to analyze the H E results and to estimate the isentropic compressibility values of the mixtures at T = 298.15 K

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Thermophysical study of 2-acetylthiophene: experimental and modelled results

Several thermophysical properties have been studied for 2-acetylthiophene: (i) vapour pressure was determined at temperatures within 336.16–445.02 K; (ii) density, speed of sound, static permittivity, refractive index, surface tension, and kinematic viscosity were measured at p = 0.1 MPa and at temperatures from 278.15 K (or 283.15 K for the refractive index) to 338.15 K; (iii) volumetric properties were also determined at temperatures in the (283.15–338.15) K range and at pressures up to 65.0 MPa. From these experimental values, different derivative properties have been calculated such as enthalpy of vaporization, isobaric expansibility, isothermal and isentropic compressibility, dipole moment, entropy and enthalpy of surface formation, and dynamic viscosity. All experimental properties were correlated and the results were explained through the intermolecular interactions. Moreover PC-SAFT EoS was used to model the thermodynamic behaviour of the compound. Finally, this EoS combined with the Density Gradient Theory allowed obtaining the influence parameter for the surface tension of 2-acetylthiophene

Optical Bistability in Nonlinear Optical Coupler with Negative Index Channel

We discuss a novel kind of nonlinear coupler with one channel filled with a negative index material (NIM). The opposite directionality of the phase velocity and the energy flow in the NIM channel facilitates an effective feedback mechanism that leads to optical bistability and gap soliton formation

Sodium flux ratio in Na/K pump-channels opened by palytoxin

© 2007 Rakowski et al. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License. The definitive version was published in Journal of General Physiology 130 (2007): 41-54, doi:10.1085/jgp.200709770.Palytoxin binds to Na+/K+ pumps in the plasma membrane of animal cells and opens an electrodiffusive cation pathway through the pumps. We investigated properties of the palytoxin-opened channels by recording macroscopic and microscopic currents in cell bodies of neurons from the giant fiber lobe, and by simultaneously measuring net current and 22Na+ efflux in voltage-clamped, internally dialyzed giant axons of the squid Loligo pealei. The conductance of single palytoxin-bound "pump-channels" in outside-out patches was ~7 pS in symmetrical 500 mM [Na+], comparable to findings in other cells. In these high-[Na+], K+-free solutions, with 5 mM cytoplasmic [ATP], the K0.5 for palytoxin action was ~70 pM. The pump-channels were ~40–50 times less permeable to N-methyl-D-glucamine (NMG+) than to Na+. The reversal potential of palytoxin-elicited current under biionic conditions, with the same concentration of a different permeant cation on each side of the membrane, was independent of the concentration of those ions over the range 55–550 mM. In giant axons, the Ussing flux ratio exponent (n') for Na+ movements through palytoxin-bound pump-channels, over a 100–400 mM range of external [Na+] and 0 to –40 mV range of membrane potentials, averaged 1.05 ± 0.02 (n = 28). These findings are consistent with occupancy of palytoxin-bound Na+/K+ pump-channels either by a single Na+ ion or by two Na+ ions as might be anticipated from other work; idiosyncratic constraints are needed if the two Na+ ions occupy a single-file pore, but not if they occupy side-by-side binding sites, as observed in related structures, and if only one of the sites is readily accessible from both sides of the membrane.This work was supported by NIH grants NS22979, NS11223, and HL36783, and National Science Foundation grant CCF- 0622158. This research was also partially funded by the Intra mural Research Program of the NIH, National Institute of Neurological Disorders and Stroke