Admittance change of squid axon during action potentials. Change in capacitive component due to sodium currents

A mathematical model for the action potential in Purkinje fibres is developed. It is based on voltage-clamp results which show that inactivation of sodium current in these muscles is much slower than in squid axon and that the latent rise in potassium conductance is not present. Both the sodium and the potassium conductances are represented as a sum of slow and fast components. This is incorporated in the suitably adjusted Hodgkin-Huxley model for the squid axon. It is shown that such a model can account satisfactorily for the shape of the action potentials in Purkinje fibres.

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The modulation of two motor behaviors by persistent sodium currents in Xenopus laevis tadpoles

Journal of Neurophysiology ◽

10.1152/jn.00755.2016 ◽

2017 ◽

Vol 118 (1) ◽

pp. 121-130 ◽

Cited By ~ 5

Author(s):

Erik Svensson ◽

Hugo Jeffreys ◽

Wen-Chang Li

Keyword(s):

Action Potentials ◽

Sodium Current ◽

Repetitive Firing ◽

Sodium Currents ◽

Spinal Neurons ◽

Motor Behaviors ◽

Low Concentrations ◽

Descending Interneurons ◽

Lateral Sclerosis

Persistent sodium currents ( INaP) are common in neuronal circuitries and have been implicated in several diseases, such as amyotrophic lateral sclerosis (ALS) and epilepsy. However, the role of INaP in the regulation of specific behaviors is still poorly understood. In this study we have characterized INaP and investigated its role in the swimming and struggling behavior of Xenopus tadpoles. INaP was identified in three groups of neurons, namely, sensory Rohon-Beard neurons (RB neurons), descending interneurons (dINs), and non-dINs (neurons rhythmically active in swimming). All groups of neurons expressed INaP, but the currents differed in decay time constants, amplitudes, and the membrane potential at which INaP peaked. Low concentrations (1 µM) of the INaP blocker riluzole blocked INaP ~30% and decreased the excitability of the three neuron groups without affecting spike amplitudes or cellular input resistances. Riluzole reduced the number of rebound spikes in dINs and depressed repetitive firing in RB neurons and non-dINs. At the behavior level, riluzole at 1 µM shortened fictive swimming episodes. It also reduced the number of action potentials neurons fired on each struggling cycle. The results show that INaP may play important modulatory roles in motor behaviors. NEW & NOTEWORTHY We have characterized persistent sodium currents in three groups of spinal neurons and their role in shaping spiking activity in the Xenopus tadpole. We then attempted to evaluate the role of persistent sodium currents in regulating tadpole swimming and struggling motor outputs by using low concentrations of the persistent sodium current antagonist riluzole.

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Action potentials of isolated single muscle fibers recorded by potential-sensitive dyes.

The Journal of General Physiology ◽

10.1085/jgp.76.6.729 ◽

1980 ◽

Vol 76 (6) ◽

pp. 729-750 ◽

Cited By ~ 16

Author(s):

S Nakajima ◽

A Gilai

Keyword(s):

Action Potentials ◽

Light Transmission ◽

Surface Membrane ◽

Muscle Fibers ◽

Single Muscle ◽

Squid Axon ◽

Vertebrate Muscle ◽

Tubular System ◽

The Difference ◽

Stimulation Of

Light transmission changes upon massive stimulation of single muscle fibers of Xenopus were studied with the potential-sensitive nonpermeant dyes, merocyanine rhodanine (WW375) and merocyanine oxazolone (NK2367). Upon stimulation an absorption change (wave a) occurred, which probably represents the sum of action potentials in the transverse tubules and surface membrane. In WW375-stained fibers wave a is a decrease in transmission over the range of 630 to 730 nm (with NK2367, over the range of 590 to 700 nm) but becomes an increase outside this range, thus showing a triphasic spectral pattern. This spectrum differs from that of the squid axon, in which depolarization produces only an increase in transmission over the whole range of wavelengths (Ross et al. 1977. J. Membr. Biol. 33:141-183). When wave a was measured at the edge of the fiber to obtain more signal from the surface membrane, the spectrum did not seem to differ markedly from that obtained from the entire width of the fiber. Thus, the difference in the spectrum between the squid axon and the vertebrate muscle cannot be attributed to the presence of the tubular system.

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Acute effects of thyroid hormone on sodium currents in neonatal myocytes

Bioscience Reports ◽

10.1007/bf01117247 ◽

1990 ◽

Vol 10 (3) ◽

pp. 309-315 ◽

Cited By ~ 17

Author(s):

W. Craelius ◽

W. L. Green ◽

D. R. Harris

Keyword(s):

Thyroid Hormone ◽

Action Potential ◽

Action Potentials ◽

Acute Exposure ◽

Na Channels ◽

Neonatal Rats ◽

Sodium Currents ◽

Acute Effects ◽

Na Current ◽

20 Nm

Sodium currents and action potentials were recorded from myocytes of neonatal rats during acute exposure to thyroid hormone (5–20 nM). One to 5 minutes after addition of thyroid hormone to the bath, decay from peak Na current was slowed, with the fractional current flowing 20 ms after onset (relative to peak current) increasing from 6±5% to 17±13% (p<0.01, n=12). Action potential durations were increased from 55±14 to 86±36 msec (p<0.05, n=6). The effects of thyroid hormone were partially reversed by lidocaine (60 μM, n=5), a specific blocker of a slow sub-population of Na channels. Thus thyroid hormone interacts directly with myocyte membrane, probably by slowing of inactivation of Na channels.

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The interactions between potassium and sodium currents in generating action potentials in the rat sympathetic neurone.

The Journal of Physiology ◽

10.1113/jphysiol.1988.sp016992 ◽

1988 ◽

Vol 397 (1) ◽

pp. 127-147 ◽

Cited By ~ 24

Author(s):

O Belluzzi ◽

O Sacchi

Keyword(s):

Action Potentials ◽

Sodium Currents

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The sodium current underlying action potentials in guinea pig hippocampal CA1 neurons.

The Journal of General Physiology ◽

10.1085/jgp.91.3.373 ◽

1988 ◽

Vol 91 (3) ◽

pp. 373-398 ◽

Cited By ~ 69

Author(s):

P Sah ◽

A J Gibb ◽

P W Gage

Keyword(s):

Action Potentials ◽

Time Course ◽

Sodium Current ◽

Hippocampal Slices ◽

Resting Potential ◽

Equilibrium Potential ◽

Sodium Currents ◽

Time To Peak ◽

Ca1 Region ◽

Inward Currents

Neurons were acutely dissociated from the CA1 region of hippocampal slices from guinea pigs. Whole-cell recording techniques were used to record and control membrane potential. When the electrode contained KF, the average resting potential was about -40 mV and action potentials in cells at -80 mV (current-clamped) had an amplitude greater than 100 mV. Cells were voltage-clamped at 22-24 degrees C with electrodes containing CsF. Inward currents generated with depolarizing voltage pulses reversed close to the sodium equilibrium potential and could be completely blocked with tetrodotoxin (1 microM). The amplitude of these sodium currents was maximal at about -20 mV and the amplitude of the tail currents was linear with potential, which indicates that the channels were ohmic. The sodium conductance increased with depolarization in a range from -60 to 0 mV with an average half-maximum at about -40 mV. The decay of the currents was not exponential at potentials more positive than -20 mV. The time to peak and half-decay time of the currents varied with potential and temperature. Half of the channels were inactivated at a potential of -75 mV and inactivation was essentially complete at -40 to -30 mV. Recovery from inactivation was not exponential and the rate varied with potential. At lower temperatures, the amplitude of sodium currents decreased, their time course became longer, and half-maximal inactivation shifted to more negative potentials. In a small fraction of cells studied, sodium currents were much more rapid but the voltage dependence of activation and inactivation was very similar.

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Sodium currents during differentiation in a human neuroblastoma cell line.

The Journal of General Physiology ◽

10.1085/jgp.97.3.521 ◽

1991 ◽

Vol 97 (3) ◽

pp. 521-539 ◽

Cited By ~ 16

Author(s):

R E Weiss ◽

N Sidell

Keyword(s):

Action Potentials ◽

Sodium Current ◽

Neuroblastoma Cell ◽

Neuroblastoma Cell Line ◽

Human Neuroblastoma Cell ◽

Sodium Currents ◽

Human Neuroblastoma ◽

Human Neuroblastoma Cell Line ◽

Induction Of Differentiation ◽

Total Sodium

The electrophysiological properties of a human neuroblastoma cell line, LA-N-5, were studied with the whole-cell configuration of the patch clamp technique before and after the induction of differentiation by retinoic acid, a vitamin A metabolite. Action potentials could be elicited from current clamped cells before the induction of differentiation, suggesting that some neuroblasts of the developing sympathetic nervous system are excitable. The action potential upstroke was carried by a sodium conductance, which was composed of two types of sodium currents, described by their sensitivity to tetrodotoxin (TTX) as TTX sensitive and TTX resistant. TTX-sensitive and TTX-resistant sodium currents were blocked by nanomolar and micromolar concentrations of TTX, respectively. The voltage sensitivity of activation and inactivation of TTX-resistant sodium current is shifted -10 to -30 mV relative to TTX-sensitive sodium current, suggesting that TTX-resistant sodium current could play a role in the initiation of action potentials. TTX-sensitive current comprised greater than 80% of the total sodium current in undifferentiated LA-N-5 cells. The surface density of total sodium current increased from 24.9 to 57.8 microA/microF after cells were induced to differentiate. The increase in total sodium current density was significant (P less than 0.05). The surface density of TTX-resistant sodium current did not change significantly during differentiation, from which we conclude that an increase in TTX-sensitive sodium current underlies the increase in total current.

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Differential Effects of NGF and BDNF on Axotomy-Induced Changes in GABAA-Receptor-Mediated Conductance and Sodium Currents in Cutaneous Afferent Neurons

Journal of Neurophysiology ◽

10.1152/jn.1997.78.1.31 ◽

1997 ◽

Vol 78 (1) ◽

pp. 31-42 ◽

Cited By ~ 61

Author(s):

Adetokunbo A. Oyelese ◽

Marco A. Rizzo ◽

Stephen G. Waxman ◽

Jeffery D. Kocsis

Keyword(s):

Sciatic Nerve ◽

Action Potential ◽

Action Potentials ◽

Afferent Neurons ◽

Sodium Currents ◽

Drg Neurons ◽

Differential Effects ◽

Action Potential Waveform ◽

Induced Changes ◽

Potential Waveform

Oyelese, Adetokunbo A., Marco A. Rizzo, Stephen G. Waxman, and Jeffery D. Kocsis. Differential effects of NGF and BDNF on axotomy-induced changes in GABAA-receptor-mediated conductance and sodium currents in cutaneous afferent neurons. J. Neurophysiol. 78: 31–42, 1997. The effects of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) on injury-induced changes in the electrophysiological properties of adult rat cutaneous afferent dorsal root ganglion (DRG) neurons were examined. Whole cell patch-clamp techniques were used to study γ-aminobutyric acid-A (GABAA)-receptor-mediated conductance, voltage-dependent sodium currents, and action potential waveform in cutaneous afferent neurons (35–60 μm diam) cultured from control and axotomized animals. Cutaneous afferent neuronswere identified by retrograde labeling with hydroxy-stilbamidine (Fluoro-gold, a fluorescent retrograde axonal tracer); the sciatic nerve was transected 1 wk after Fluoro-gold injection and L4/L5 DRG neurons were cultured 2–3 wk after axotomy. NGF, BDNF, or Ringer (vehicle) solution was delivered in vivo directly to the transected sciatic nerve stump in axotomized rats via an osmotic pump. Recordings were obtained from neurons 5–24 h after culture. Axotomized neurons from rats treated with vehicle solution displayed a twofold increase in GABA-induced conductance and a prominent reduction in the proportion of neurons expressing action potentials that had inflections on the falling phase. The expression of kinetically slow tetrodotoxin (TTX)-resistant sodium current was markedly reduced and an increased expression of kinetically fast TTX-sensitive current was observed in neurons from vehicle-treated, axotomized rats. Treatment with NGF (0.25 μg/μl at 12 μl/day for 14 days) in axotomized animals resulted in an increase in the proportion of neurons expressing TTX-resistant, slow sodium currents and inflected action potentials, but had no effect on GABA-induced conductance. Treatment with BDNF (0.5 μg/μl at 12 μl/day for 14 days) attenuated the axotomy-induced increase in GABAA-receptor-mediated conductance while minimally affecting action potential waveform. The observed neurotrophin effects occurred independently of cell size changes. These findings indicate a differential regulation of GABAA receptor and sodium channel properties in axotomized rat cutaneous afferent neurons by specific neurotrophic factors.

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