Analysis of Spike Electrogenesis and Depolarizing K Inactivation in Electroplaques of <i>Electrophorus electricus</i>, L

Nakamura, Yutaka; Nakajima, Shigehiro; Grundfest, Harry

doi:10.1085/jgp.49.2.321

Cited by 113 publications

(95 citation statements)

References 32 publications

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“…Such steady-state negative resistance characteristics have been observed in a number of other preparations (4)(5)(6)(7)(8). In contrast to the negative resistance seen for intact axons of the North Atlantic squid, Loligo pealii, a linear steady-state current-voltage relation has been found for internally perfused axons of the Chilean squid, Docidicus gigas (9).…”

Section: Introductionmentioning

confidence: 52%

Removal of Potassium Negative Resistance in Perfused Squid Giant Axons

Lecar

Ehrenstein

Binstock

et al. 1967

The Journal of General Physiology

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A~STRACT Squid giant axons, internally and externally perfused with solutions having potassium as the only cation, exhibit an approximately linear steady-state current-voltage relation. When small amounts of calcium and magnesium are present in the external potassium solution, the current-voltage curve is markedly nonlinear, exhibiting the rectification and negative resistance which have been observed for intact axons in isosmotic potassium solutions. The effects of perfusion and removal of external divalent cations are interpreted in terms of two components of current, a linear component and a nonlinear time-varying component. The former is increased and the latter diminished by the removal of the external divalent cations.

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Section: Introductionmentioning

confidence: 52%

Removal of Potassium Negative Resistance in Perfused Squid Giant Axons

Lecar

Ehrenstein

Binstock

et al. 1967

The Journal of General Physiology

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“…The innervated face is held against a Mylar sheet which partitions two pools of Ringer's solution; the sheet contains a window that exposes part of the innervated face to one of the pools (9). Currents are passed between platinum plates in each pool, traversing the window and the exposed region of the innervated face (4,10). The temperature was 15°unless otherwise noted.…”

Section: Methodsmentioning

confidence: 99%

Relaxation measurements on the acetylcholine receptor.

Sheridan¹,

Lester²

1975

Proc. Natl. Acad. Sci. U.S.A.

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In Electrophorus electroplaques, the agonist-induced postsynaptic conductance depends on membrane potential. During steady exposure to agonists, after a voltage step the conductance relaxes on a millisecond time scale, exponentially approaching a new equilibrium value. The relaxation rate constant k is an instantaneous function of voltage, insensitive to the past or present conductance.Two components sum to form k. A concentration-sensitive component increases linearly with agonist concentration and decreases during desensitization or exposure to curare. Thus this component reflects the average frequency at which acetylcholine receptors are opening.The voltage-sensitive component, obtained by extrapolating k to zero agonist concentration, increases at more positive potentials. For acetylcholine, the voltage-sensitive component equals the rate constant for the exponential decay of postsynaptic currents; it thus seems to be the closing rate for active receptors. The voltage-sensitive component has the relative amplitudes acetylcholine < carbamoylcholine < decamethonium, and for each agonist equals the closing rate determined from "noise" measurements at neuromuscular junctions.The kinetic data explain several aspects of the steady-state conductance induced by agonists, but shed no light on apparent cooperative effects.At a nicotinic synapse, when an agonist reaches the postsynaptic membrane, the acetylcholine receptors produce an increase in membrane conductance. In the presence of a steady agonist concentration, the receptors form an equilibrium population. At a given time, some receptors are in an "open" state (or possibly in one of two such states); other receptors are in one or more "closed" states (1, 2).It is not yet certain which molecular events (binding of agonist, conformational change in the receptor protein, etc.) govern the transitions between the active and inactive states. In order to gain more information on these rate-limiting steps, we have applied two relaxation techniques to the acetylcholine receptors of eel electroplaques. "Voltage-jump" experiments are based on the fact that, for a steady agonist concentration, the equilibrium between "open" and "closed" receptors also depends upon the potential across the postsynaptic membrane (2-4). The proportion of open receptors increases as the potential becomes more negative. Thus, when one rapidly changes the membrane potential from one level to another, the agonist-induced conductance relaxes to a new value, with a time course which reflects the kinetics of the transition is between "open" and "closed" receptors.The second experiment derives from the observation that, at the frog neuromuscular junction, endplate currents ordinarily last much longer than the acetylcholine concentration in the synaptic cleft (5-8). Thus the declining phase of the endplate current is the response of receptors to an instantaneous removal of acetylcholine. We report here that the declining phase of eel postsynaptic currents has precisely the same significance.We...

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“…The inward-going rectification has been known as anomalous rectification in vertebrate striated muscle (Katz, 1949;Hodgkin & Horowicz, 1959;Nakajima, Iwasaki & Obata, 1962;Adrian & Freygang, 1962a;Adrian, Chandler & Hodgkin, 1970) and in cardiac muscle (Hall, Hutter & Noble, 1963;Hutter & Noble, 1960; Noble, 1965;Noble & Tsien, 1968), or as K inactivation in the electroplaque of the eel (Grundfest, 1960(Grundfest, , 1961(Grundfest, , 1966; Nakamura, Nakajima & Grundfest, 1965). The functional significance of the inward-going rectification is not known.…”

Section: Introductionmentioning

confidence: 99%

Analysis of non‐linearity observed in the current—voltage relation of the tunicate embryo

Miyazaki¹,

Takahashi²,

Tsuda³

et al. 1974

The Journal of Physiology

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SUMMARY1. In the gastrula of the tunicate (Halocynthia aurantium) the resting potential ofthe embryonic membrane was about -70 mV in both std ASW and Na-free ASW.2. The potential responses to depolarizing current in the early gastrula embryo showed distinct potential jumps from about -50 to about + 40 mV during the application of current and from about 0 to resting level after its cessation thus forming a plateau at about 0 mV. Those jumps were not altered significantly by the removal of both Na and Ca ions from ASW except for the duration of the plateau after the cessation of current. 3. Blastomeres in an embryo were tightly coupled with each other electrotonically at the blastula and gastrula stages. The fact that the coupling ratio was nearly 1t0 made it reasonable to treat an embryo as one cell as far as electrical properties are concerned.4. The I-V relation of the embryonic membrane consisted of an inward rectifying region, outward rectifying region and transitional zone between the two, resulting in a S-shaped curve as in the egg cell membrane. But in the gastrula embryo, the transitional zone actually included the discontinuous part of the I-V curve (from about -50 to about + 40 mV) due to the potential jump.5. The ionic current (Ii) during the potential jump in Na-free ASW was estimated from the slope of the potential response based on the assumption of constant capacitance during the membrane potential changes. The S. MIYAZAKI AND OTHERS calculated Ii-V curve complemented the interrupted I-V curve smoothly and showed the existence of a negative resistance region from about -50 to about 0 mV in the steady-state I-V relation.6. The steady-state I-V relation was altered significantly by changing the K concentration in ASW, and the existence of the negative resistance can be reasonably explained by the marked inward-going rectification or anomalous rectification of K conductance.7. The replacement of K with Rb in ASW produced the marked suppression of the inward-going rectification of the embryonic membrane.

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Analysis of Spike Electrogenesis and Depolarizing K Inactivation in Electroplaques of Electrophorus electricus, L

Cited by 113 publications

References 32 publications

Removal of Potassium Negative Resistance in Perfused Squid Giant Axons

Removal of Potassium Negative Resistance in Perfused Squid Giant Axons

Relaxation measurements on the acetylcholine receptor.

Analysis of non‐linearity observed in the current—voltage relation of the tunicate embryo

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