scholarly journals Interaction of DDT with the Components of Lobster Nerve Membrane Conductance

1968 ◽  
Vol 51 (2) ◽  
pp. 177-198 ◽  
Author(s):  
Toshio Narahashi ◽  
Hans G. Haas
Keyword(s):  
Steady State ◽  
Action Potentials ◽  
Membrane Conductance ◽  
Transient Current ◽  
Nerve Membrane ◽  
Exponential Functions ◽  
Time To Peak ◽  
Cardiac Action ◽  
Steady State Current ◽  
Single Exponential Function

The falling phase of action potential of lobster giant axons is markedly prolonged by treatment with DDT, and a plateau phase appears as in cardiac action potentials. Repetitive afterdischarge is very often superimposed on the plateau. Voltage-clamp experiments with the axons treated with DDT and with DDT plus tetrodotoxin or saxitoxin have revealed the following: DDT markedly slows the turning-off process of peak transient current and suppresses the steady-state current. The falling phase of the peak transient current in the DDT-poisoned axon is no longer expressed by a single exponential function as in normal axons, but by two or more exponential functions with much longer time constants. The maximum peak transient conductance is not significantly affected by DDT. DDT did not induce a shift of the curve relating the peak transient conductance to membrane potential along the potential axis. The time to peak transient current and the time for the steady-state current to reach its half-maximum are prolonged by DDT to a small extent. The finding that, under the influence of DDT, the steady-state current starts flowing while the peak transient current is partially maintained supports the hypothesis of two operationally separate ion channels in the nerve membrane.

scholarly journals Transient Current Density in a Pair of Long Parallel Conductors

2021 ◽  
Vol 11 (15) ◽  
pp. 6920
Author(s):  
Oldřich Coufal
Keyword(s):  
Steady State ◽  
Cross Section ◽  
Current Density ◽  
Circular Cross Section ◽  
Transient Current ◽  
Constant Current ◽  
Voltage Source ◽  
Sinusoidal Voltage ◽  
Steady State Current ◽  
Maximum Current

Two infinitely long parallel conductors of arbitrary cross section connected to a voltage source form a loop. If the source voltage depends on time, then due to induction there is no constant current density in the loop conductors. It is only recently that a method has been published for accurately calculating current density in a group of long parallel conductors. The method has thus far been applied to the calculation of steady-state current density in a loop connected to a sinusoidal voltage source. In the present article, the method is used for an accurate calculation of transient current using transient current density. The transient current is analysed when connecting and short-circuiting the sources of sinusoidal, constant and sawtooth voltages. For circular cross section conductors, the dependences of maximum current density, maximum current and the time of achieving steady state on the source frequency, the distance of the conductors and their resistivity when connecting the source of sinusoidal voltage are examined.

scholarly journals Comparison of Tetrodotoxin and Procaine in Internally Perfused Squid Giant Axons

1967 ◽  
Vol 50 (5) ◽  
pp. 1413-1428 ◽  
Author(s):  
Toshio Narahashi ◽  
Nels C. Anderson ◽  
John W. Moore
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Ionic Current ◽  
Transient Current ◽  
Resting Potential ◽  
Giant Axons ◽  
Time To Peak ◽  
Sucrose Gap ◽  
High Concentrations ◽  
Very High

Squid giant axons were internally perfused with tetrodotoxin and procaine, and excitability and electrical properties were studied by means of current-clamp and sucrose-gap voltage-clamp methods. Internally perfused tetrodotoxin was virtually without effect on the resting potential, the action potential, the early transient membrane ionic current, and the late steady-state membrane ionic current even at very high concentrations (1,000–10,000 nM) for a long period of time (up to 36 min). Externally applied tetrodotoxin at a concentration of 100 nM blocked the action potential and the early transient current in 2–3 min. Internally perfused procaine at concentrations of 1–10 mM reversibly depressed or blocked the action potential with an accompanying hyperpolarization of 2–4 mv, and inhibited both the early transient and late steady-state currents to the same extent. The time to peak early transient current was increased. The present results and the insolubility of tetrodotoxin in lipids have led to the conclusion that the gate controlling the flow of sodium ions through channels is located on the outer surface of the nerve membrane.

scholarly journals Current- and Voltage-Clamped Studies on Myxicola Giant Axons

1969 ◽  
Vol 54 (6) ◽  
pp. 730-740 ◽  
Author(s):  
L. Binstock ◽  
L. Goldman
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Action Potential ◽  
Voltage Clamp ◽  
Transient Current ◽  
Resting Membrane Potential ◽  
Action Potential Amplitude ◽  
Giant Axons ◽  
Potential Amplitude ◽  
Steady State Current

A new dissection procedure for preparing Myxicola giant axons for observation under voltage clamp is described. Preparation time is generally 40–45 min. 65–70% of the preparations attempted may be brought through the entire procedure, including insertion of the long internal electrode, and support an initial action potential amplitude of 100 mv or greater. Mean values for axon diameter, resting membrane potential, action potential amplitude, maximum peak inward transient current, and resting membrane resistance are 560 µ, —66.5 mv, 112 mv, 0.87 ma/cm2 and 1.22 KΩ cm 2 respectively. Cut branches do not seem to be a problem in this preparation. Behavior under voltage clamp is reasonably stable over several hours. Reductions in maximum inward transient current of 10% and in steady-state current of 5–10% are expected in the absence of any particular treatment. Tetrodotoxin blocks the action potential and both the inward and outward transient current, but has no effect on either the resting membrane potential or the steady-state current. This selective action of tetrodotoxin on the transient current is taken as an indication that this current component is probably carried by Na.

Graded responses and spiking properties of identified first-order visual interneurons of the fly compound eye

1995 ◽  
Vol 73 (5) ◽  
pp. 1782-1792 ◽  
Author(s):  
R. O. Uusitalo ◽  
M. Juusola ◽  
M. Weckstrom
Keyword(s):  
Steady State ◽  
Action Potentials ◽  
Compound Eye ◽  
Function Analysis ◽  
Resting Potential ◽  
Current Step ◽  
First Order ◽  
Positive Current ◽  
Transfer Function Analysis ◽  
Steady State Current

1. We studied the graded and spiking properties of the "non-spiking" first-order visual interneurons of the fly compound eye in situ with the use of intracellular recordings. Iontophoretical QX-314 injections, Lucifer yellow marking, and (discontinuous) current-clamp method together with transfer function analysis were used to characterize the neural signal processing mechanisms in these neurons. 2. A light-OFF spike was seen in one identified anatomic subtype (L3, n = 6) of the three first-order visual interneurons (L1, L2, and L3, or LMCs) when recorded from synaptic region (i.e., in the 1st visual ganglion, lamina ganglionaris) in dark-adapted conditions. Hyperpolarization of the membrane potential by current caused the identified L1 (n = 4), as well as L3 (n = 6), to produce an OFF spike, a number of action potentials, and some subthreshold depolarizations after the light-ON response. In L2 the OFF spike or action potentials could not be elicited. 3. To produce action potentials in L1 and L3, it was found to be necessary to hyperpolarize the cells approximately 35-45 mV (n = 43) below the resting potential (RP) in the synaptic zone. Recordings from the axons of these cells revealed that near the second neuropil (chiasma) the threshold of these spikes was near to (approximately 10 mV below, n = 16) or even at the RP when an ON spike was also produced (n = 4). 4. The recorded spikes were up to 54 mV in amplitude, appeared with a maximum frequency of up to 120 impulses/s, and had a duration of approximately 8 ms. In L1 and L3 the spikes were elicited either after a light pulse (L3) or after a negative current step that was superimposed on a hyperpolarizing steady-state current (L3 and L1). A positive current step (similarly superimposed on a hyperpolarizing steady-state current) also triggered the spikes during the step. 5. Iontophoretic injection of a potent intracellularly effective blocker of voltage-gated sodium channels, QX-314, irreversibly eradicated the spikes and subthreshold depolarizations (n = 5). In addition, further injections elongated the light-ON responses and decreased or even abolished the light-OFF response. 6. Negative prepulses followed by positive current steps were applied from the RP, to test the activation-inactivation properties of the channels responsible for the OFF spike.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals The transport mechanism of the human sodium/myo-inositol transporter 2 (SMIT2/SGLT6), a member of the LeuT structural family

2014 ◽  
Vol 307 (5) ◽  
pp. C431-C441 ◽  
Author(s):  
Louis J. Sasseville ◽  
Jean-Philippe Longpré ◽  
Bernadette Wallendorff ◽  
Jean-Yves Lapointe
Keyword(s):  
Steady State ◽  
Conformational Changes ◽  
Voltage Pulse ◽  
Transport Mechanism ◽  
Simulated Annealing Algorithm ◽  
Transient Current ◽  
Xenopus Laevis Oocytes ◽  
Structural Family ◽  
Novel Approach ◽  
Steady State Current

The sodium/ myo-inositol transporter 2 (SMIT2) is a member of the SLC5A gene family, which is believed to share the five-transmembrane segment inverted repeat of the LeuT structural family. The two-electrode voltage-clamp (TEVC) technique was used to measure the steady-state and the pre-steady-state currents mediated by human SMIT2 after expression in Xenopus laevis oocytes. Phlorizin is first shown to be a poor inhibitor of pre-steady-state currents for depolarizing voltage pulse. From an up to threefold difference between the apparent ON and OFF transferred charges during a voltage pulse, we also show that a fraction of the transient current recorded for very negative potentials is not a true pre-steady-state current coming from the cotransporter conformational changes. We suggest that this transient current comes from a time-dependent leak current that can reach large amplitudes when external Na+ concentration is reduced. A kinetic model was generated through a simulated annealing algorithm. This algorithm was used to identify the optimal connectivity among 19 different kinetic models and obtain the numerical values of the associated parameters. The proposed 5-state model includes cooperative binding of Na+ ions, strong apparent asymmetry of the energy barriers, a rate-limiting step that is likely associated with the translocation of the empty transporter, and a turnover rate of 21 s−1. The proposed model is a proof of concept for a novel approach to kinetic modeling of electrogenic transporters and allows insight into the transport mechanism of members of the LeuT structural family at the millisecond timescale.

Intrinsic properties of deep dorsal horn neurons in the L6-S1 spinal cord of the intact rat

1995 ◽  
Vol 74 (5) ◽  
pp. 1819-1827 ◽  
Author(s):  
M. C. Jiang ◽  
C. L. Cleland ◽  
G. F. Gebhart
Keyword(s):  
Spinal Cord ◽  
Steady State ◽  
Membrane Potential ◽  
Dorsal Horn ◽  
Action Potentials ◽  
Time Course ◽  
Inward Rectification ◽  
Current Voltage ◽  
Steady State Current ◽  
Current Passage

1. Stable intracellular recordings were obtained from neurons (n = 62) in the L6-S1 deep dorsal horn of the spinal cord in pentobarbital-sodium-anesthetized, intact rats (n = 26). All neurons responded to natural mechanical stimuli and/or electrical stimulation of peripheral afferents. 2. Intracellular penetrations were maintained for 30 min-2 h. Action potentials occurred spontaneously in most neurons (n = 50) and could be evoked in the remainder (n = 12) by depolarizing current passage. Mean resting membrane potential was -60.9 mV, mean action potential height amplitude was 75.2 mV, mean half-width of the action potentials was 0.33 ms, mean input resistance was 38 M omega, and mean time constant was 9.1 ms. 3. Action potentials were followed by afterpotentials made up of at least three components; a fast afterhyperpolarization (fAHP), a slow afterhyperpolarization (sAHP), and an afterdepolarization (ADP). Most neurons (n = 40) exhibited all three afterpotentials, although some displayed only a fAHP and an ADP (n = 10) or a fAHP and a sAHP (n = 12). The durations and magnitudes of the afterpotentials varied widely among neurons. 4. Steady-state current-voltage relations were investigated in 14 neurons with depolarizing and hyperpolarizing current pulses. Of these 14 neurons, 5 exhibited inward rectification, 3 had outward rectification, and the remaining 6 showed a predominantly linear change of membrane potential to current injection. In addition, several neurons (n = 9) exhibited a postinhibitory rebound that was sometimes (n = 4) accompanied by a "sag" in voltage during the preceding hyperpolarizing current step. 5. Four patterns of spike frequency adaptation occurred during step depolarizing current passage. The firing of most neurons gradually decreased with a simple, approximately exponential time course (n = 21), in some neurons it decreased with both a fast and a slow time course (n = 8), in several it incremented in rate (n = 3), and one neuron showed a complex combination of multiple decrementing and incrementing adaptations. Time constants, magnitude of adaptation, and the slopes of the steady-state current-voltage relation varied widely. 6. Oscillations in membrane potential and firing rate occurred in three neurons. The oscillations arose from endogenous mechanisms in at least one neuron because manipulation of membrane potentials altered the frequency of oscillation; a depolarizing current increased the period of oscillation and eventually produced tonic firing, and a hyperpolarizing current increased the frequency of oscillation and eventually terminated firing. 7. The results demonstrate that neurons in the L6-S1 region of the dorsal horn exhibit a diversity of cellular mechanisms that may significantly modulate normal somatosensory and visceral input.

New Molecular Scaffolds for Fluorescent Voltage Indicators

2018 ◽  
Author(s):  
Steven Boggess ◽  
Shivaani Gandhi ◽  
Brian Siemons ◽  
Nathaniel Huebsch ◽  
Kevin Healy ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Action Potentials ◽  
Induced Pluripotent Stem Cell ◽  
Molecular Wire ◽  
Voltage Sensing ◽  
Design Synthesis ◽  
Cardiac Action ◽  
Action Potential Waveform ◽  
Induced Pluripotent ◽  
Voltage Sensing Domain

<div> <p>The ability to non-invasively monitor membrane potential dynamics in excitable cells like neurons and cardiomyocytes promises to revolutionize our understanding of the physiology and pathology of the brain and heart. Here, we report the design, synthesis, and application of a new class of fluorescent voltage indicator that makes use of a fluorene-based molecular wire as a voltage sensing domain to provide fast and sensitive measurements of membrane potential in both mammalian neurons and human-derived cardiomyocytes. We show that the best of the new probes, fluorene VoltageFluor 2 (fVF 2) readily reports on action potentials in mammalian neurons, detects perturbations to cardiac action potential waveform in human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes, shows a substantial decrease in phototoxicity compared to existing molecular wire-based indicators, and can monitor cardiac action potentials for extended periods of time. Together, our results demonstrate the generalizability of a molecular wire approach to voltage sensing and highlights the utility of fVF 2 for interrogating membrane potential dynamics.</p> </div>

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