Membrane phosphate headgroups' modulation of permeation of alkaline cations in gramicidin channels.

The function of membrane proteins is modulated by lipid bilayers. The permeation of ions in gramicidin A channels (gA) is markedly distinct in monoglyceride and phospholipid membranes. It was previously demonstrated that membrane phosphate headgroups accelerate the rate of proton transfer in gA.

Enhancement of proton transfer in ion channels by membrane phosphate headgroups.

The transfer of protons (H+) in gramicidin (gA) channels is markedly distinct in monoglyceride and phospholipid membranes. In this study, the molecular groups that account for those differences were investigated using a new methodology. The rates of H+ transfer were measured in single gA channels reconstituted in membranes made of plain ceramides or sphingomyelins and compared to those in monoglyceride and phospholipid bilayers.

Proton transfer in water wires in proteins: modulation by local constraint and polarity in gramicidin a channels.

The transfer of protons in membrane proteins is an essential phenomenon in biology. However, the basic rules by which H(+) transfer occurs in water wires inside proteins are not well characterized. In particular, the effects of specific atoms and small groups of atoms on the rate of H(+) transfer in water wires are not known.

Proton transfer in gramicidin water wires in phospholipid bilayers: attenuation by phosphoethanolamine.

The transfer of protons in water wires was studied in native gramicidin A (gA), and in the SS- and RR-diastereoisomers of dioxolane-linked gA channels (SS and RR channels). These peptides were incorporated into membranes comprised of distinct combinations of phospholipid headgroups and acyl chains. Quantitative relationships between single channel conductances to H+ (g(H)) and [H+] were determined in distinct phospholipid membranes, and are in remarkable contrast with results previously obtained in monoglyceride membranes.

Et tu, Grotthuss! and other unfinished stories.

This review article is divided into three sections. In Section 1, a short biographical note on Freiherr von Grotthuss is followed by a detailed summary of the main findings and ideas present in his 1806 paper. Attempts to place Grotthuss contribution in the context of the science done at his time were also made.

The transfer of protons in water wires inside proteins.

The translocation of protons across membrane proteins is an essential phenomenon in biology. Only in recent years however, have we started to study in detail some of the basic features of proton transfer in water molecules inside proteins at the single molecule level. Due to their truly unique features, gramicidin-based ion channels have been used to probe proton transfer in both experimental and computational fronts.

Kinetic isotope effects of proton transfer in aqueous and methanol containing solutions, and in gramicidin A channels.

The electrochemical conductivities of HCL and DCI were measured in: H(2)O and D(2)O; in methanol and fully deuterated methanol; and in water-methanol solutions. The single channel conductances to H(+) (g(H)) and D(+) (g(D)) in various gramicidin A (gA) ion channels incorporated in glycerylmonooleate planar bilayers were also measured. Kinetic isotope effects (KIE) were estimated from the ratio of conductivity measurements.

Theoretical study of the structure and dynamic fluctuations of dioxolane-linked gramicidin channels.

Gramicidin is a hydrophobic peptide that assembles as a head-to-head dimer in lipid membranes to form water-filled channels selective to small monovalent cations. Two diastereoisomeric forms, respectively SS and RR, of chemically modified channels in which a dioxolane ring links the formylated N-termini of two gramicidin monomers, were shown to form ion channels. To investigate the structural basis underlying experimentally measured differences in proton conductance in the RR and SS channels, we construct atomic-resolution models of dioxolane-linked gramicidin dimers by analogy with the native dimer.

Proton transfer in gramicidin channels is modulated by the thickness of monoglyceride bilayers.

The thickness of monoglyceride planar bilayers has significant effects on the transfer of protons in both native gramicidin A (gA) and in covalently linked SS- and RR-dioxolane-linked gA proteins. Planar bilayers with various thicknesses were formed from an appropriate combination of monoglyceride with various fatty acid lengths and solvent. Bilayer thicknesses ranged from 25 A (monoolein in squalene) to 54 A (monoeicosenoin in decane).

On the origin of closing flickers in gramicidin channels: a new hypothesis.

The submillisecond closing events (flickers) and the single channel conductances to protons (g(H)) were studied in native gramicidin A (gA) and in the SS and RR diastereoisomers of dioxolane-linked gA channels in planar bilayers. Bilayers were formed from glycerylmonooleate (GMO) in various solvents. In GMO/decane (thick) bilayers, the largest flicker frequency occurred in the SS channel (39 s(-1)), followed by the RR (4 s(-1)) and native gA channels (3 s(-1)).

Thermodynamic view of activation energies of proton transfer in various gramicidin A channels.

The temperature dependencies (range: 5-45 degrees C) of single-channel proton conductances (g(H)) in native gramicidin A (gA) and in two diastereoisomers (SS and RR) of the dioxolane-linked gA channels were measured in glycerylmonooleate/decane (GMO) and diphytanoylphosphatidylcholine/decane (DiPhPC) bilayers. Linear Arrhenius plots (ln (g(H)) versus K(-1)) were obtained for the native gA and RR channels in both types of bilayers, and for the SS channel in GMO bilayers only. The Arrhenius plot for proton transfer in the SS channel in DiPhPC bilayers had a break in linearity around 20 degrees C.

Modulation of proton transfer in the water wire of dioxolane-linked gramicidin channels by lipid membranes.

Proton conductance (g(H)) in single SS stereoisomers of dioxolane-linked gramicidin A (gA) channels were measured in different phospholipid bilayers at different HCl concentrations. In particular, measurements were obtained in bilayers made of 1,2-diphytanoyl 3-phosphocholine (DiPhPC) or its ethylated derivative 1,2-diphytanoyl 3-ethyl-phosphocholine (et-DiPhPC,). The difference between these phospholipids is that in et-DiPhPC one of the phosphate oxygens is covalently linked to an ethyl group and cannot be protonated.

Covalently linked gramicidin channels: effects of linker hydrophobicity and alkaline metals on different stereoisomers.

The direct role of the dioxolane group on the gating and single-channel conductance of different stereoisomers of the dioxolane-linked gramicidin A (gA) channels reconstituted in planar lipid bilayers was investigated. Four different covalently linked gA dimers were synthesized. In two of them, the linker was the conventional dioxolane described previously (SS and RR channels).

Gating and permeation in ion channels formed by gramicidin A and its dioxolane-linked dimer in Na(+) and Cs(+) solutions.

The association of two gramicidin A (gA) peptides via H-bonds in lipid bilayers causes the formation of an ion channel that is selective for monovalent cations only. In this study, two gAs were covalently linked with a dioxolane group (SS dimer). Some functional properties of natural gA channels were compared to that synthetic dimer in Na(+)- or Cs(+)-containing solutions.

Proton mobilities in water and in different stereoisomers of covalently linked gramicidin A channels.

Proton conductivities in bulk solution (lambda(H)) and single-channel proton conductances (g(H)) in two different stereoisomers of the dioxolane-linked gramicidin A channel (the SS and RR dimers) were measured in a wide range of bulk proton concentrations ([H], 0.1-8000 mM). Proton mobilities (micro(H)) in water as well as in the SS and RR dimers were calculated from the conductivity data.

The conduction of protons in different stereoisomers of dioxolane-linked gramicidin A channels.

Two different stereoisomers of the dioxolane-linked gramicidin A (gA) channels were individually synthesized (the SS and RR dimers;. Science. 244:813-817).

Attenuation of proton currents by methanol in a dioxolane-linked gramicidin A channel in different lipid bilayers.

The mobility of protons in a dioxolane-linked gramicidin A channel (D1) is comparable to the mobility of protons in aqueous solutions (Cukierman, S., E. P.

Proton conduction in gramicidin A and in its dioxolane-linked dimer in different lipid bilayers.

Gramicidin A (gA) molecules were covalently linked with a dioxolane ring. Dioxolane-linked gA dimers formed ion channels, selective for monovalent cations, in planar lipid bilayers. The main goal of this study was to compare the functional single ion channel properties of natural gA and its covalently linked dimer in two different lipid bilayers and HCl concentrations (10-8000 mM).

Direct modulation of Na+ currents by protein kinase C activators in mouse neuroblastoma cells.

We investigated the effects of different protein kinase C (PKC) activators on Na+ currents using the conventional whole-cell and the inside-out macropatch voltage-clamp techniques in mouse neuroblastoma cells (N1E-115). Two different categories of PKC activators were investigated: the cis-unsaturated fatty acids (CUFAs): oleic (cis-9-octadecenoic), linoleic (cis-9-12-octadecadienoic), and linolenic acid (cis-9-12-15-octadecatrienoic), and, the diacylglycerol (DAG) derivative 1-2-dioctanoyl-sn-glycerol (DOG). These substances caused the following alterations on Na+ currents: (i) Na+ currents were attenuated as a function of voltage.

Diacylglycerol-induced activation of protein kinase C attenuates Na+ currents by enhancing inactivation from the closed state.

The causes of attenuation of Na+ currents by diacylglycerol (DAG)-induced protein kinase C (PKC) activation in mouse neuroblastoma N1E-115 cells were investigated using the cell-attached patch, and the perforated-patch (nystatin based) whole-cell voltage-clamp techniques. Activation of PKC by DAG attenuated Na+ currents. Attenuation occurred in the absence of significant changes in the time-course of Na+ currents.

Multiple effects of protein kinase C activators on Na+ currents in mouse neuroblastoma cells.

The effects of externally applied different protein kinase C (PKC) activators on Na+ currents in mouse neuroblastoma cells were studied using the perforated-patch (nystatin-based) whole cell voltage clamp technique. Two diacylglycerol-like compounds, OAG (1-oleoyl-2-acetyl-sn-glycerol), and DOG (1-2-dioctanoyl-rac-glycerol) attenuated Na+ currents without affecting the time course of activation or inactivation. The reduction in Na+ current amplitude caused by OAG or DOG was dependent on membrane potential, being more intense at positive voltages.

Effects of extracellular sodium, quinidine, and ryanodine on slow response excitability in rabbit atrial trabeculae.

1. We investigated Na(+)-Ca2+ exchange and the involvement of the sarcoplasmic reticulum in frequency-dependent slow response excitability enhancement in rabbit atrial trabeculae. 2.

Barium modulates the gating of batrachotoxin-treated Na+ channels in high ionic strength solutions.

Batrachotoxin-activated rat brain Na+ channels were reconstituted in neutral planar phospholipid bilayers in high ionic strength solutions (3 M NaCl). Under these conditions, diffuse surface charges present on the channel protein are screened. Nevertheless, the addition of extracellular and/or intracellular Ba2+ caused the following alterations in the gating of Na+ channels: (a) external (or internal) Ba2+ caused a depolarizing (or hyperpolarizing) voltage shift in the gating curve (open probability versus membrane potential curve) of the channels; (b) In the concentration range of 10-120 mM, extracellular Ba2+ caused a larger voltage shift in the gating curve of Na+ channels than intracellular Ba2+; (c) voltage shifts of the gating curve of Na+ channels as a function of external or internal Ba2+ were fitted with a simple binding isotherm with the following parameters: for internal Ba2+, delta V0.

K-current mediation of prolactin-induced proliferation of malignant (Nb2) lymphocytes.

The effects of different concentrations of various K-current blockers on prolactin-induced proliferation and membrane K-currents in malignant lymphocytes (Nb2 cells) were investigated. Membrane currents were measured with the whole cell patch-clamp technique, and lymphocyte density was quantified by both spectrophotometric and conventional methods. K-current blockers tested (quinidine, 4-aminopyridine, barium, and tetraethylammonium) exhibited similar rank order potency for K-current block and inhibition of prolactin-induced proliferation of malignant lymphocytes.