Potential clamp analysis of membrane currents in rat myelinated nerve fibres.

Brismar, Tom

doi:10.1113/jphysiol.1980.sp013074

Cited by 197 publications

(97 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…We found a TTX-sensitive component restricted to the preterminal part of the endings whose time course (allowing for differences in temperature) closely agrees with that of the Na current reconstructed from voltage-clamp data by Chiu et al (1979) (Chiu et al 1979;Brismar, 1980). We failed to detect any TTX-sensitive component in membrane currents generated at the terminal part ofthe endings.…”

Section: Discussionmentioning

confidence: 57%

“…However, recent reports on data obtained from mammalian nodes of Ranvier have shown that the repolarizing phase of the action potential depends mainly on Na inactivation and leakage conductance, the role of K conductance being negligible (Nonner & Stiimpfli, 1969;Chiu, Ritchie, Rogart & Stagg, 1979;Brismar, 1980; but see Binah & Palti, 1981). Similarly, only large diameter fibres from amphibian nerves seem to display a nodal delayed K conductance, while small ones appear devoid of it (Smith & Schauf, 1981).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Presynaptic currents in mouse motor endings

Brigant

Mallart

1982

The Journal of Physiology

255

180

View full text Add to dashboard Cite

SUMMARY1. We used external electrodes placed under precise visual control on motor endings of the mouse to record electrical activity promoted by nerve stimulation.2. Three types of wave form have been observed in relation to well-defined electrode emplacements: (i) at the transition between myelinated and non-myelinated parts of the axon, the wave form consists of two negative deflexions preceded by a small positivity (preterminal response), (ii) at the main part of the terminal branches, we obtained a two component positive wave form (terminal response) and (iii) electrode positions in a narrow area between the former and the latter yielded triphasic (positive-negative-positive) wave forms (intermediate responses).3. Since these responses could not be readily interpreted in terms of classical description of membrane currents associated with propagating action potentials, we used specific channel blocking agents to identify wave form components.4. Bath application of tetraethylammonium or aminopyridines, or, better, a combination of both, suppressed delayed positive deflexions of terminal and intermediate responses and the late negative component of preterminal responses. Local inophoretic drug application showed that K channels are present only at the terminal part of the endings. K+ outflux promotes a local circuit whose sink is located at the preterminal part where it generates the late negative deflexion of the preterminal response.5. Local application of tetrodotoxin suppressed the first negative component of preterminal responses but failed to affect electrical activity at the terminal part of the endings. This indicates that Na channels, and, therefore, action potential generation, are restricted to the preterminal part.6. Suppression of K conductance revealed a slow inward current at the terminal part of the endings which could be identified as a Ca current. Ba2+ and Sr2+ could substitute for Ca2+ as inward current carriers.7. Activation of spatially separated Na channels, on one side, and of K and Ca channels, on the other, generated ionic currents and separated local circuit currents which flow between preterminal and terminal parts (and vice versa). Thus, the signals recorded at-each point of motor endings correspond to the sum of ionic and passive currents entering (or leaving) the membrane at that point.8. The present results represent a further example of heterogeneity of axonal membrane.

show abstract

Section: Discussionmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Presynaptic currents in mouse motor endings

Brigant

Mallart

1982

The Journal of Physiology

255

180

View full text Add to dashboard Cite

show abstract

“…In addition, 100 j, tmol/1 4-AP clearly enhanced the duration of the B-and C-fibre compound potentials in the isolated vagus nerve. The lack of effect on the vagus A-fibre potential may be explained by an absence of repolarizing potassium currents in these fibres as has been shown for single, rabbit (Chiu et al 1979) and rat (Brismar 1980) myelinated axons.…”

Section: A) 4-aminopyridinementioning

confidence: 73%

Presynaptic actions of 4-Aminopyridine and γ-aminobutyric acid on rat sympathetic ganglia in vitro

Galvan

Grafe

Bruggencate

1980

Naunyn-Schmiedeberg's Arch. Pharmacol.

View full text Add to dashboard Cite

Summary.Responses to bath-applications of 4-aminopyridine (4-AP) and y-aminobutyric acid (GABA) were recorded intracellularly from neurones in the rat isolated superior cervical ganglion.4-aminopyridine (0.1 -1.0 mmol/1) usually induced spontaneous action potentials and excitatory postsynaptic potentials (EPSPs), which were blocked by hexamethonium. Membrane potential was unchanged; spike duration was slightly increased. Vagus nerve B-and C-fibre potentials were prolonged.In 4-AP solution (0.1 -0.3 mmol/1), GABA (0.1 mmol/1), 3-aminopropanesulphonic acid or muscimol evoked "bursts" of spikes and EPSPs in addition to a neuronal depolarization. These "bursts", which were not elicited by glycine, glutamate, taurine or (+)-baclofen, were completely antagonised by hexamethonium, tetrodotoxin or bicuculline methochloride.It is concluded that: (a)4-AP has a potent presynaptic action on sympathetic ganglia; (b) presynaptic actions of GABA can be recorded postsynaptically in the presence of 4-AP; and (c) the presynaptic GABAreceptors revealed in this condition are similar to those on the postsynaptic membrane.

show abstract

“…In these investigations the properties of sodium currents were found to be similar to those in 6-2 amphibian nerve fibres, whereas the potassium currents in fibres of warm-blooded animals were significantly smaller or even entirely lacking. More details on the kinetics and steady-state properties of sodium currents in mammalian nerve fibres were recently reported by Chiu, Ritchie, Rogart & Stagg (1979) for rabbit and by Brismar (1980) for rat. In their experiments the curve relating sodium permeability and membrane potential was found to be shifted by about 10 mV in the hyperpolarizing direction compared with amphibian fibres.…”

Section: Introductionmentioning

confidence: 99%

Sodium currents and sodium‐current fluctuations in rat myelinated nerve fibres

Neumcke

Stämpfli

1982

The Journal of Physiology

132

View full text Add to dashboard Cite

SUMMARY1. Sodium currents and fluctuations of sodium currents were measured in myelinated fibres of rat sciatic nerve under voltage clamp at 20 'C.2. Relaxations of sodium currents during various test potentials were recorded in the presence of 6 nM-TTX in the extracellular solution. The activation of sodium currents at low depolarizations could be described with the m2 formulation. At increasing potentials higher powers of m up to 4 were required. The mid-point of the PNa(E) curve was located near E = -32 mV. Sodium inactivation during various depolarizations developed in two phases.3. The resistance in series with the nodal membrane was calculated from peak sodium currents without and with 6 nM-TTX in the extracellular solution. The resistance varied between different fibres and ranged between 190 and 620 k.Q.4. From peak sodium currents at the same membrane potential without and in the presence of TTX an apparent equilibrium dissociation constant of 1-6 nm was calculated for TTX binding to sodium channels.5. The conductance y and the number No (corrected for series-resistance effects) of sodium channels were evaluated from ensemble average values of the mean sodium current and the variance of sodium-current fluctuations at the beginning of a test pulse. The mean values were y = 14-5 pS, No = 21,000 per node.6. The spectral density of stationary sodium-current fluctuations exhibited two relaxation components whose time constants were comparable to those of sodium activation and inactivation. At low depolarizations the variance produced by inactivation fluctuations was larger than predicted by the m3 . h formulation.7. It is concluded that individual sodium channels of rat and frog nerve have similar gating properties. In mammalian nodes the number of sodium channels is lower and the single-channel conductance higher than in amphibian nodes.

show abstract

Potential clamp analysis of membrane currents in rat myelinated nerve fibres.

Cited by 197 publications

References 21 publications

Presynaptic currents in mouse motor endings

Presynaptic currents in mouse motor endings

Presynaptic actions of 4-Aminopyridine and γ-aminobutyric acid on rat sympathetic ganglia in vitro

Sodium currents and sodium‐current fluctuations in rat myelinated nerve fibres

Contact Info

Product

Resources

About