Sodium channel permeation in squid axons. I: Reversal potential experiments.

Begenisich, Ted; Cahalan, Michael D.

doi:10.1113/jphysiol.1980.sp013432

Cited by 119 publications

(125 citation statements)

References 42 publications

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“…VOLUME 85 -1985 site from the internal membrane surface. This estimate assumes the Na channel to be a one-ion pore (Hille, 1975) under these experimental conditions (however, see Begenisich and Cahalan, 1980). The average fractional electrical distance determined in this manner was 0.10 ± 0.02 (three axons) .…”

Section: Resultsmentioning

confidence: 99%

“…Possible interactions between blocking cations and the Na conductance pathway have serious practical implications for the use of ionic substitutes that may otherwise be presumed to be inert (see, e.g., Begenisich and Cahalan, 1980). In particular, experimental substitution of internal K by certain cations is frequently used to eliminate contributions of ion movement through K channels from ionic current records under voltage clamp.…”

Section: Introductionmentioning

confidence: 99%

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Interactions of monovalent cations with sodium channels in squid axon. I. Modification of physiological inactivation gating.

Yeh

Oxford

1985

The Journal of General Physiology

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Inactivation of Na channels has been studied in voltage-clamped, internally perfused squid giant axons during changes in the ionic composition of the intracellular solution. Peak Na currents are reduced when tetramethylammonium ions (TMA+) are substituted for Cs ions internally . The reduction reflects a rapid, voltage-dependent block of a site in the channel by TMA+. The estimated fractional electrical distance for the site is 10% of the channel length from the internal surface. Na tail currents are slowed by TMA' and exhibit kinetics similar to those seen during certain drug treatments . Steady state INa is simultaneously increased by TMA*, resulting in a "cross-over" of current traces with those in Cs' and in greatly diminished inactivation at positive membrane potentials . Despite the effect on steady state inactivation, the time constants for entry into and exit from the inactivated state are not significantly different in TMA' and Cs'. Increasing intracellular Na also reduces steady state inactivation in a dose-dependent manner . Ratios of steady state IN. to peak INa vary from^-0.14 in Cs'-or K''-perfused axons to^-0.4 in TMA+-or Na'-perfused axons. These results are consistent with a scheme in which TMA' or Na' can interact with a binding site near the inner channel surface that may also be a binding or coordinating site for a natural inactivation particle . A simple competition between the ions and an inactivation particle is, however, not sufficient to account for the increase in steady state INa, and changes in the inactivation process itself must accompany the interaction of TMA' and Na' with the channel.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Interactions of monovalent cations with sodium channels in squid axon. I. Modification of physiological inactivation gating.

Yeh

Oxford

1985

The Journal of General Physiology

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“…Parts C and D of Fig. 14 (Hille, 1975;Begenisich & Cahalan, 1980). Energies, G, of the barriers and wells are given in dimensionless units, multiplied by R, the gas constant, and T, the absolute temperature.…”

Section: A Molecular Interpretation Of the Kinetic Effects Of Tnbsmentioning

confidence: 99%

Chemical modification of potassium channel gating in frog myelinated nerve by trinitrobenzene sulphonic acid.

Cahalan¹,

Pappone²

1983

The Journal of Physiology

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SUMMARY1. We investigated the actions ofexternally applied trinitrobenzene sulphonic acid (TNBS) on the K currents of voltage-clamped frog myelinated nerve fibres. TNBS treatment irreversibly slowed the tail currents for K channel closing up to 10-fold. Time constants for the tail currents appear shifted 60-80 mV in the hyperpolarizing direction following TNBS treatment.2. The time course of K channel opening was unaffected for depolarizing pulses to potentials positive to -20 mV. For smaller pulses to potentials between -80 and -30 mV the activation time course was slower following TNBS treatment.3. TNBS had little or no effect on the steady-state conductance-voltage relation of K channels determined from tail current amplitude. The instantaneous currentvoltage relation for K channels and potency ofblock by external TEA were unaffected by TNBS.4. K tail currents showed fast and slow components both before and after TNBS treatment. Reaction with TNBS caused the fast component to decline in amplitude and the slow component to increase both in magnitude and time constant. The rate of reaction increased with increasing pH.5. Full expression ofaltered K channel kinetics depends upon the ionic composition of the external solution. Tail currents were up to 10-fold slower when measured in 1 7-5 mM-K than when measured with 80 % of the external K replaced by Na.6. The differential effects ofTNBS on K channel closing and opening were modelled in a three-state kinetic scheme, with an increase in the energy barrier for closing an open channel following TNBS treatment.

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“…Previous work (Chandler & Meves, 1965;Cahalan & Begenisich, 1976) and the first paper in this series (Begenisich & Cahalan, 1980) have shown that the selectivity of Na channels appears to depend on the concentration of many different permeant ions applied at the axoplasmic membrane surface. Concentration-dependent selectivity is but one of several permeation properties that cannot be accounted for within the Nernst-Planck and Goldman-Hodgkin-Katz formulations of electrodiffusion in membranes.…”

Section: Introductionmentioning

confidence: 99%

Sodium channel permeation in squid axons. II: Non‐independence and current‐voltage relations.

Begenisich¹,

Cahalan²

1980

The Journal of Physiology

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SUMMARY1. The concentration and voltage dependence of current through the Na channels of squid giant axons was studied. The permeant cations Na, K and ammonium were used.2. The Na channel current at a fixed voltage saturates as the internal permeant ion concentration is increased. The half-saturation activities at 50 mV were found to be 623, 268, 161 mm for Na, NH4, and K, respectively. These Km values for Na and K appear to be voltage-dependent.3. Instantaneous current-voltage relations were determined with two different internal Na concentrations and with Na outside and K inside.4. A three-barrier, two-site ion permeation model previously used in describing Na channel reversal potentials is shown here to account for the Na channel currents as well.

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Sodium channel permeation in squid axons. I: Reversal potential experiments.

Cited by 119 publications

References 42 publications

Interactions of monovalent cations with sodium channels in squid axon. I. Modification of physiological inactivation gating.

Interactions of monovalent cations with sodium channels in squid axon. I. Modification of physiological inactivation gating.

Chemical modification of potassium channel gating in frog myelinated nerve by trinitrobenzene sulphonic acid.

Sodium channel permeation in squid axons. II: Non‐independence and current‐voltage relations.

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