Guanidinium analogues as probes of the squid axon sodium pore. Evidence for internal surface charges.

Smith-Maxwell, Catherine; Begenisich, Ted

doi:10.1085/jgp.90.3.361

Cited by 12 publications

(11 citation statements)

References 28 publications

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“…Based on results on sodium channel gating obtained with the squid giant axon (Chandler et al, 1965) and frog myelinated nerve (Hille et al, 1975), the extracellular and intracellular channel (or membrane) surfaces appear to differ in apparent charge density. (In fact, the charge distribution at either surface is likely to be inhomogeneous, as Smith-Maxwell and Begenisich [1987] found that the apparent charge density in the vicinity of the intracellular channel entrance in the squid giant axon differed approximately fourfold from the charge density deduced from gating experiments.) With respect to channel gating, the apparent charge density at the extracellular surface was estimated to be three to five times larger than that of the intracellular surface (Hille et al, 1975).…”

Section: Channel Asymmetry and Electrolyte-dependent Gating Shiftsmentioning

confidence: 99%

Steady-state gating of batrachotoxin-modified sodium channels. Variability and electrolyte-dependent modulation.

Chabala

Urban

Weiss

et al. 1991

The Journal of General Physiology

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A B S T RA CTThe steady-state gating of individual batrachotoxin-modified sodium channels in neutral phospholipid bilayers exhibits spontaneous, reversible changes in channel activation, such that the midpoint potential (V~) for the gating curves may change, by 30 mV or more, with or without a change in the apparent gating valence (za). Consequently, estimates for V a and, in particular, z a from ensembleaveraged gating curves differ from the average values for V, and z~ from singlechannel gating curves. In addition to these spontaneous variations, the average Va shifts systematically as a function of [NaCI] (being -109, -88, and -75 mV at 0.1, 0.5, and 1.0 M NaCI), with no systematic variation in the average z a (~ 3.7). The [NaC1]-dependent shifts in V~ were interpreted in terms of screening of fixed charges near the channels' gating machinery. Estimates for the extracellular and intracellular apparent charge densities (~ =-0.7 and cr~ =-0.08 e/nm ~) were obtained from experiments in symmetrical and asymmetrical NaCI solutions using the Gouy-Chapman theory. In 0.1 M NaCI the extracellular and intracellular surface potentials are estimated to be -94 and -17 mV, respectively. The intrinsic midpoint potential, corrected for the surface potentials, is thus about -30 mV, and the standard free energy of activation is approximately -12 kJ/mol. In symmetrical 0.I M NaCI, addition of 0.005 M Ba 2+ to the extracellular solution produced a 17-mV depolarizing shift in V a and a slight reduction in z a. The shift is consistent with predictions using the Gouy-Chapman theory and the above estimate for ~e. Subsequent addition of 0.005 M Ba 2÷ to the intracellular solution produced a ~ 5-mV hyperpolarizing shift in the ensemble-averaged gating curve and reduced z, by ~ 1. This Ba2+-induced shift is threefold larger than predicted, which together with the reduction in z, implies that Ba 2+ may bind at the intracellular channel surface.

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Section: Channel Asymmetry and Electrolyte-dependent Gating Shiftsmentioning

confidence: 99%

Steady-state gating of batrachotoxin-modified sodium channels. Variability and electrolyte-dependent modulation.

Chabala

Urban

Weiss

et al. 1991

The Journal of General Physiology

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“…The open channel current obtained in the presence of a blocking divalent cation, I, was fit to the following relation (Smith-Maxwell and Begenisich, 1987;MacKinnon et al, 1989),…”

Section: Ion Channel Blockade and Surface Chargementioning

confidence: 99%

Ion conduction in substates of the batrachotoxin-modified Na+ channel from toad skeletal muscle

Naranjo

Latorre

1993

Biophysical Journal

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Batrachotoxin-modified Na+ channels from toad muscle were inserted into planar lipid bilayers composed of neutral phospholipids. Single-channel conductances were measured for [Na+] ranging between 0.4 mM and 3 M. When membrane preparations were made in the absence of protease inhibitors, two open conductance states were identified: a fully open state (16.6 pS in 200 mM symmetrical NaCl) and a substate that was 71% of the full conductance. The substate was predominant at [Na+] > 65 mM, whereas the presence of the fully open state was predominant at [Na+] < 15 mM. Addition of protease inhibitors during membrane preparation stabilized the fully open state over the full range of [Na+] studied. In symmetrical Na+ solutions and in biionic conditions, the ratio of amplitudes remained constant and the two open states exhibited the same permeability ratios of PLi/PNa and PCs/PNa. The current-voltage relations for both states showed inward rectification only at [Na+] < 10 mM, suggesting the presence of asymmetric negative charge densities at both channel entrances, with higher charge density in the external side. An energy barrier profile that includes double ion occupancy and asymmetric charge densities at the channel entrances was required to fit the conductance-[Na+] relations and to account for the rectification seen at low [Na+]. Energy barrier profiles differing only in the energy peaks can give account of the differences between both conductance states. Estimation of the surface charge density at the channel entrances is very dependent on the ion occupancy used and the range of [Na+] tested. Independent evidence for the existence of a charged external vestibule was obtained at low external [Na+] by identical reduction of the outward current induced by micromolar additions of Mg2+ and Ba2+.

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“…Surface potential is the potential difference between the membrane surface and the bulk aqueous phase and is dependent on the density of interfacial charged molecules (for a review see McLaughlin, 1989). In biological membranes, this potential is on the order of a few tens of mV and might have an important role in affecting the conductance of channels in the membrane (Dani, 1986;Jordan, 1987; Kell and DeFelice, 1988), determining the structure of proteins (Gilson and Honig, 1988;Honig et al, 1986;Huang and Warshel, 1988;Perutz, 1978) and in the binding of charged molecules to the membrane (Green and Andersen, 1986;Green et al, 1987;Smith-Maxwell and Begenisich, 1987). impact on cell membrane biology is not well appreciated.…”

Section: Introductionmentioning

confidence: 99%

Dual-wavelength ratiometric fluorescence measurement of the membrane dipole potential

Gross

Bedlack

Loew

1994

Biophysical Journal

260

241

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The electrostatic potentials associated with cell membranes include the transmembrane potential (delta psi), the surface potential (psi s), and the dipole potential (psi D). psi D, which originates from oriented dipoles at the surface of the membrane, rises steeply just within the membrane to approximately 300 mV. Here we show that the potential-sensitive fluorescent dye 1-(3-sulfonatopropyl)-4-[beta[2-(di-n-octylamino)-6- naphthyl]vinyl]pyridinium betaine (di-8-ANEPPS) can be used to measure changes in the intramembrane dipole potential. Increasing the content of cholesterol and 6-ketocholestanol (KC), which are known to increase psi D in the bilayer, results in an increase in the ratio, R, of the dye fluorescence excited at 440 nm to that excited at 530 nm in a lipid vesicle suspension; increasing the content of phloretin, which lowers psi D, decreases R. Control experiments show that the ratio is insensitive to changes in the membrane's microviscosity. The lack of an isosbestic point in the fluorescence excitation and emission spectra of the dye at various concentrations of KC and phloretin argues against 1:1 chemical complexation between the dye and KC or phloretin. The macromolecular nonionic surfactant Pluronic F127 catalyzes the insertion of KC and phloretin into lipid vesicle and cell membranes, permitting convenient and controlled modulation of dipole potential. The sensitivity of R to psi D is 10-fold larger than to delta psi, whereas it is insensitive to changes in psi S. This can be understood in terms of the location of the dye chromophore with respect to the electric field profile associated with each of these potentials. These results suggest that the gradient in dipole potential occurs over a span s5 A, a short distance below the membrane-water interface. These approaches are easily adaptable to study the influence of dipole potentials on cell membrane physiology.

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Guanidinium analogues as probes of the squid axon sodium pore. Evidence for internal surface charges.

Cited by 12 publications

References 28 publications

Steady-state gating of batrachotoxin-modified sodium channels. Variability and electrolyte-dependent modulation.

Steady-state gating of batrachotoxin-modified sodium channels. Variability and electrolyte-dependent modulation.

Ion conduction in substates of the batrachotoxin-modified Na+ channel from toad skeletal muscle

Dual-wavelength ratiometric fluorescence measurement of the membrane dipole potential

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