Die Wirkung von Tetra�thylammoniumchlorid auf die Membranstr�me Ranvierscher Schn�rringe von Xenopus laevis

SUMMARY1. Intra-axonal recordings were obtained from myelinated axons innervating a lizard skeletal muscle.2. Bath application of tetraethylammonium (TEA, 1-10 mM) depolarized the resting potential, prolonged the action potential and increased the amplitude and duration of the ensuing passive depolarizing after-potential (DAP) in a dosedependent and reversible manner. TEA increased the axonal input resistance and the slow time constant of the passive voltage response, not only in depolarized axons, but also in resting and hyperpolarized axons. The resting input resistance was tripled in 10 mM-TEA.3. TEA's effects on the resting potential and action potential usually approached a steady state within 5 min, whereas TEA's effects on input resistance and on the amplitude and time course of the DAP increased progressively for 10-15 min or more, and persisted for 10-15 min after removal of TEA from the bath.4. 4-Aminopyridine (4-AP, 1 mM), which prolonged the action potential by about the same extent as 10 mM-TEA, did not depolarize the resting potential or increase the resting input resistance, and produced a much smaller increase in DAP time course than 10 mM-TEA. Gallamine (1 mM) had effects more similar to those of TEA.5. These results suggest that the resting input conductance and DAP time course in lizard motor axons are controlled in part by K+ channels that are blocked by TEA and gallamine, but not by 4-AP. The slow development of the TEA-induced increase in input resistance and DAP time course suggests that some of these channels are located in paranodal or internodal axolemma.6. In TEA and gallamine additional depolarizing potentials were superimposed on the falling phase of the action potential and on the passive DAP. These superimposed potentials were abolished by 1 mM-Mn2+, and were probably caused by Ca2+ influx into motor terminals.

Section: Tea Increases Axonal Input Resistance and The Slow Passive Tmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Effects of tetraethylammonium on the depolarizing after‐potential and passive properties of lizard myelinated axons.

Barrett

Morita

Scappaticci

1988

“…After mounting the fibre one internode was cut to decrease the resistance of the current path. The dimensions of the chamber and the method of recording membrane currents under voltage clamp conditions have been described in detail (Koppenhofer, 1967); the method is based on that of Dodge & Frankenhaeuser (1958).…”

Section: Methodsmentioning

confidence: 99%

The rate of action of tetrodotoxin on myelinated nerve fibres of Xenopus laevis and Rana esculenta

Schwarz¹,

Ulbricht²,

Wagner³

1973

105

SUMMARY1. The experiments were done on single Ranvier nodes of Xenopus laevis (voltage clamp) and Rana esculenta (action potentials). Rate and size of the effect of tetrodotoxin were determined by the reversible reduction of either the sodium inward current (Xenopus) or of VN, the maximum rate of rise of the action potential (Rana).2. The results of tetrodotoxin block at equilibrium could be excellently fitted by assuming a one-to-one reaction between toxin molecules and sodium channels of the Xenopus membrane with an equilibrium dissociation constant K = 3-60 nm at room temperature. TA was not linearly related to the fraction of unblocked sodium channels and 10-9 nM tetrodotoxin was necessary on the average to reduce ,Ato 50 % in Rana motor fibres; in sensory fibres a lower concentration sufficed.3. Onset and offset of the tetrodotoxin effect on Xenopus nodes could be quantitatively interpreted as being determined by the rates of the tetrodotoxin channel reaction. Experiments with 3-1 and 15-5 nm tetrodotoxin at room temperature yielded an association rate constant, kj, of 2-94 x 106 m-1 sec-' and a dissociation rate constant, k2, of 1-42 x 10-2sec-1. In these experiments the equilibrium dissociation constant, K, was 3-31 nM. If determined solely from the onset in the two tetrodotoxin concentrations, ki = 3-25 x 106 M-1 sec-' and K = k2/kl = 4-08 nm was calculated.4. In Rana fibres the onset and offset of TA reduction by 15-5 and 31 nm tetrodotoxin was evaluated using the equilibrium effects of intermediary tetrodotoxin concentrations for calibration. The average results at room temperature were k, = 4 x 106 M-1 see', k2 = 1-4 x 10-2 sec-' and K = 3-4nM. 168 J. R. SCHWARZ, W. ULBRICHT AND H.-H. WAGNER 5. The very short latency with which IA started to decline when tetrodotoxin was suddenly applied proved that the toxin had ready access to the membrane.6. The temperature dependence of k1, k2 and K in the Xenopus experiments could be described by Arrhenius plots yielding activation energies, Ea, of 9-8, 20-5 and 7 0 kcal/mole, respectively, corresponding to Q10 values of 1-82, 3-42 and 1P53 (between 12 and 220 C). For k1, determined from onset alone, Ea = 13-7 kcal/mole (Q10 = 2.25) was obtained. Although in Rana the temperature dependence of the rate constants could not be determined directly, the Q10 for k2 must have been of the order of 3.7. The results suggest that the rate of the toxin action on the nodal membrane of Xenopus and Rana is limited by the tetrodotoxin-sodium site reaction.

“…The possibility that TEA might have a similar action in skeletal muscle has not been examined, because of the difficulties in clamping the sodium current over much of the potential range used in the present experiments. But it seems quite possible that TEA might have some action here, not only by analogy with the work of Koppenh6fer (1967) on Xenopus node, but also because Hagiwara & Watanabe (1955) demonstrated that TEA AND MUSCLE DELA YED RECTIFICATION TEA was able to substitute partly for sodium in the generation of the action potential.…”

Section: Introductionmentioning

confidence: 99%

“…Aside from its curariform actions (Raventos, 1937), it has the effect in many nerve preparations of reducing the time dependent changes in potassium conductance which occur when the surface membrane is depolarized (e.g. squid axon: Tasaki & Hagiwara, 1957;Armstrong & Binstock, 1965; node of Ranvier preparations from amphibia: Schmidt & Stimpfii, 1966;Hille, 1967;Koppenh6fer, 1967; sub-and supra-oesophageal ganglion cells of a pulmonate mollusc Onchidium: Hagiwara & Saito, 1959; supramedullary cells of the puffer-fish Spheroides: Nakajima, 1966). …”

Section: Introductionmentioning

confidence: 99%

The effect of the tetraethylammonium ion on the delayed currents of frog skeletal muscle

Stanfield¹

1970

136

111

SUMMARY1. A method which permitted control of the membrane potential near the end of a muscle fibre and measurement of an approximation of the membrane current was used to investigate the effects of the tetraethylammonium (TEA) ion on the delayed outward potassium current obtained on depolarizing.2. Assuming Ri to be 250 Q cm and a fibre diameter of 80,u, the mean value for the maximum potassium conductance (H) was 23-2 + 3X2 mmho. cm-2.3. 58 mM-TEA, in two series of experiments, reduced gK by about 90 %.A concentration-effect relation for TEA in its action on the delayed rectifier could be fitted by a curve for a drug-receptor complex assuming one molecule of TEA to combine reversibly with one receptor, and a dissociation constant of 8 x 103 M.4. TEA tended to shift the threshold for delayed rectification to slightly more negative membrane potentials. TEA caused a similar shift in the relation between nOO and membrane potential, but did not much alter the form of the relation.5. The relation between n'0 and membrane potential and between r.-1 and membrane potential were well fitted by the model of Adrian, Chandler & Hodgkin (1970a) assuming that the Q10 was 2-5. 6. TEA slowed the rate of onset of the delayed potassium currents, decreasing Tn-1 (the reciprocal of the time constant of the fourth power function which described the current's development) by about 80 %.7. The inactivation of the delayed current with time was shown to follow a complex time course. A fast phase decays with a time constant of 270 msec and a slow phase with a time constant of 2-3 see at a membrane potential of + 10 mV.8. The fast phase of the delayed current is much more susceptible to the action of TEA than the slow phase, and these are interpreted in terms of different potassium channels. TEA has little effect on the time constant with which either the fast current or the slow current inactivates.