[Ionic mechanism of noradrenaline-induced membrane potential changes of neurones in toad dorsal root ganglion].
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The membrane conductance and reversal potential were determined for neurones in toad dorsal root ganglion (DRG) with intracellular recording technique during depolarization or hyperpolarization induced by noradrenaline (NA). The effects of blocking agents for potassium or calcium channels on NA-induced membrane potential responses were examined. In 15 neurones, the NA-induced depolarization was accompanied by a 32.6% decrease of membrane conductance; in other 4 neurones, the depolarization was accompanied by an initial increase and subsequent decrease in membrane conductance. The NA hyperpolarization was associated with an increase of membrane conductance by 16.2% (n = 8). The mean reversal potential of NA-induced depolarization was -88.5 +/- 0.9 mV (means +/- SE, n = 4). The NA-induced hyperpolarization was nullified at -89 to -92 mV of membrane potentials (n = 3). Tetraethylammonium superfusion enhanced NA depolarization amplitude by 73.7 +/- 11.9% (means +/- SE, n = 7) and depressed NA hyperpolarization amplitude by 40.5% (n = 4). Intracellular injection of CsCl increased phenylephrine-induced depolarization by 34.5% (n = 4). MnCl2 superfusion decreased the amplitudes of NA-induced depolarization by 50.5 +/- 9.9% (means +/- SE, n = 10), and of NA-induced hyperpolarization by 89.5 +/- 4.9% (means +/- SE, n = 7) respectively. The results suggest that the depolarization or hyperpolarization induced by NA might be mediated by the alteration in activation of K+ or Ca2+ channels.Keywords:
Hyperpolarization
Tetraethylammonium
Reversal potential
Dorsal root ganglion
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1. When the retina of the toad, Bufo marinus, was superfused with 6‐12 mM‐tetraethylammonium chloride (TEA), intracellular recordings from rods showed large, depolarizing regenerative potentials. For brief exposures to TEA, these potentials occurred during the recovery phase of the light responses; whereas, during longer exposures, they were spontaneous in darkness but suppressed during illumination. Similar regenerative potentials were observed during perfusion with 3‐10 mM‐4‐aminopyridine and 1‐2 mM‐BaCl2. 2. The amplitude of the regenerative potentials depended upon the extracellular Ca concentration ([Ca2+]o). Lowering [Ca2+]o decreased their amplitude and in zero [Ca2+]o they were reversibly abolished. Increasing [Ca2+]o by 1.5‐2 times produced a small hyperpolarization of membrane potential and a large augmentation in regenerative response amplitude. However, larger increases in [Ca2+]o produced large membrane hyperpolarizations and reversibly suppressed the regenerative responses. 3. High concentrations of Sr2+ in TEA also enhanced regenerative activity but did not affect the rod resting membrane potential. The amplitude of regenerative potentials increased continuously with increasing [Sr2+]o, and in 28 mM‐Sr2+ the rods generated 60‐70 mV action potentials, even in the absence of extracellular Na+. 4. The regenerative potentials were blocked by 25 microM‐Cd2+, 50‐100 microM‐Co2+, 5mM‐Mg2+, and 100 microM‐D‐600. They were unaffected by 2 microM‐TTX or 2‐5 mM‐Na aspartate. 5. In Ringer containing 12 mM‐TEA, large anode break responses could be recorded from rods at the termination of inward current pulses. These anode break responses were also suppressed by Co2+ and unaffected by TTX or Na aspartate. 6. We conclude that the membrane of toad rods contains a conductance normally selective for Ca2+, which is activated by depolarization. In normal Ringer, the inward current through this conductance produces little effect, since it is balanced by a large outward current, probably carried by K+. TEA and other agents appear to block this outward current, permitting the Ca2+ current to become regenerative.
Hyperpolarization
Tetraethylammonium chloride
Bufo marinus
Tetraethylammonium
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Squid giant axon
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The membrane actions of substance P (SP) and the effects on the Ca‐dependent action potential of dorsal horn neurones have been investigated by means of intracellular recording techniques in the immature rat in vitro spinal cord slice preparation. Bath application of SP (2 X 10(‐6) to 1 X 10(‐5) M) induced a biphasic membrane response consisting of an initial hyperpolarization followed by a depolarization in about one‐third of the cells examined. Initial hyperpolarization was not observed when synaptic activity was blocked by perfusing the slice with a tetrodotoxin‐containing or low Ca, high Mg Ringer solution. This result is consistent with a presynaptic action of SP mediated through excitation of inhibitory interneurones. This interpretation was supported by recording of repetitive spontaneous inhibitory post‐synaptic potential (i.p.s.p.)‐like hyperpolarizing potentials during the initial hyperpolarization. When Co ions were used to block voltage‐dependent Ca conductance and possible indirect presynaptic actions, SP induced only a small depolarization of membrane potential. It seems, therefore, that Ca conductance may have contributed to the depolarizing phase of the SP response, either through its mediation of synaptic transmission or through direct effects as a charge carrier for inward current. When tetrodotoxin was used, the SP‐induced increase in neuronal input resistance was not modified, although depolarization was slightly diminished. In contrast, in medium containing tetrodotoxin and tetraethylammonium, the SP‐depolarizing response was enhanced and accompanied by a small decrease in input resistance and firing of Ca spikes. These results suggest that SP‐induced depolarization might be a consequence of a reduction in a voltage‐dependent K conductance allowing Na and/or Ca conductances to dominate. SP modified the duration of Ca‐dependent action potentials of dorsal horn neurones, the most consistent change being an initial dose‐dependent and reversible decrease in the spike duration. The decrease in Ca spike duration was associated with a small reduction in the rate of rise and peak amplitude, and a significant parallel increase in dV/dt of the falling phase of the Ca spike. Our data indicate that the initial decrease in Ca spike duration was not due to the depolarizing action of SP, although shunting of the membrane resistance, either through presynaptic or post‐synaptic mechanisms, has not been ruled out. Alternatively, these data are consistent with the possibility that SP shortens the duration of the Ca spike by decreasing a voltage‐sensitive inward Ca current and/or augmenting an outward K current.(ABSTRACT TRUNCATED AT 400 WORDS)
Hyperpolarization
Tetrodotoxin
Tetraethylammonium
Reversal potential
Spike potential
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ABSTRACT Small, brief mechanical stimuli were delivered with a microstylus to the surface of Paramecium caudatum bathed in solutions of 1 mM-CaCl2, 1 mM KC1 +1 mM Tris HC1, pH 7 2. Stimulation of the caudal end produced a graded hyperpolarizing receptor potential which reached a maximum within 50 msec and decayed more slowly. The input conductance at the peak of the caudal receptor potential increased to a value of at least 6 times that of the resting membrane. The potential diminished in amplitude when the membrane was hyperpolarized by injected d.c. current, and reversed sign with sufficient hyperpolarization. The reversal potential in a solution of 1 mM-CaCl2 + 4 mM-KCl was − 37 mV, while the resting potential was − 20 mV. The peak of the receptor potential was shifted about + 50 mV per 10-fold increase in extracellular K+. C−and Ca2+ and other cations produced little or no shift in the potential peak of the response. It is concluded that mechanical stimulation of the caudal surface produces a local increase in conductance, predominantly to K+. Extracellular tetraethylammonium converts the normally hyperpolarizing receptor potential to a depolarization similar to the potential produced in response to mechanical stimulation of the anterior surface. The TEA effect is antagonized by calcium ions.
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Tetraethylammonium
Hyperpolarization
Reversal potential
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Intracellular recordings were made from red nucleus (r.n.) neurones in guinea‐pig slice preparations in vitro. In the control solution, a fast action potential was elicited by a depolarizing current pulse. This fast action potential was abolished by tetrodotoxin (TTX). When tetraethylammonium (TEA) was added to the perfusing solution, a TTX‐resistant slow action potential was elicited by a large depolarizing current pulse. This TTX‐resistant slow action potential was abolished by Co2+ or Mn2+. In the control solution, the action potential was followed by a fast and a slow after‐hyperpolarization (a.h.p.). The fast a.h.p. was abolished by TEA. The amplitude of the fast a.h.p. was dependent on the extracellular K+ concentration. The slow a.h.p. was reversibly abolished by Co2+ or Mn2+. The reversal potential of the slow a.h.p. was dependent on the extracellular K+ concentration. When the membrane potential was hyperpolarized, a time‐dependent inward rectification was observed. This inward rectification was inhibited by Cs+ but not by Ba2+, TTX, TEA or Co2+. It is concluded that the fast action potential is produced by a voltage‐dependent Na+ conductance, the TTX‐resistant slow action potential is produced by a voltage‐dependent Ca2+ conductance, the fast a.h.p. is produced by a voltage‐dependent K+ conductance, the slow a.h.p. is produced by a Ca2+‐activated K+ conductance and the inward rectification is produced by a time‐dependent inward rectifier in r.n. neurones.
Tetraethylammonium
Tetrodotoxin
Hyperpolarization
Reversal potential
Tetraethylammonium chloride
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Interleukin 1β
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The membrane conductance and reversal potential were determined for neurones in toad dorsal root ganglion (DRG) with intracellular recording technique during depolarization or hyperpolarization induced by noradrenaline (NA). The effects of blocking agents for potassium or calcium channels on NA-induced membrane potential responses were examined. In 15 neurones, the NA-induced depolarization was accompanied by a 32.6% decrease of membrane conductance; in other 4 neurones, the depolarization was accompanied by an initial increase and subsequent decrease in membrane conductance. The NA hyperpolarization was associated with an increase of membrane conductance by 16.2% (n = 8). The mean reversal potential of NA-induced depolarization was -88.5 +/- 0.9 mV (means +/- SE, n = 4). The NA-induced hyperpolarization was nullified at -89 to -92 mV of membrane potentials (n = 3). Tetraethylammonium superfusion enhanced NA depolarization amplitude by 73.7 +/- 11.9% (means +/- SE, n = 7) and depressed NA hyperpolarization amplitude by 40.5% (n = 4). Intracellular injection of CsCl increased phenylephrine-induced depolarization by 34.5% (n = 4). MnCl2 superfusion decreased the amplitudes of NA-induced depolarization by 50.5 +/- 9.9% (means +/- SE, n = 10), and of NA-induced hyperpolarization by 89.5 +/- 4.9% (means +/- SE, n = 7) respectively. The results suggest that the depolarization or hyperpolarization induced by NA might be mediated by the alteration in activation of K+ or Ca2+ channels.
Hyperpolarization
Tetraethylammonium
Reversal potential
Dorsal root ganglion
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1. The electrophysiological properties of testosterone‐secreting cells (i.e. Leydig cells) in the mouse were studied using patch electrodes. The cells appeared solitarily or in clusters after mechanical dissociation from testes. They were confirmed to be Leydig cells on the basis of 3 beta‐hydroxysteroid dehydrogenase staining. 2. Under current‐clamp conditions in the whole‐cell configuration, Leydig cells immersed in standard saline were able to generate action potential‐like responses. The active responses occurred after cessation of membrane hyperpolarization or when cells were held in a hyperpolarized condition and stimulated with depolarizing current pulses. 3. In Leydig cells under voltage clamp, depolarizations more positive than ‐50 mV evoked transient inward currents which decayed completely during the duration of depolarization (130 ms). No obvious outward currents were evoked by pulses less positive than 30 mV. 4. The inward currents were identified as Ca2+ current, since replacement of external Ca2+ with Mn2+ reversibly diminished the current whereas Ba2+ or Sr2+ substituted for Ca2+. 5. With voltage pulses more positive than 40 mV, outward currents were evoked. The currents were dependent on K+ concentration and were blocked by quinine or tetraethylammonium. The amplitudes of outward currents were increased with raised internal Ca2+ concentration. 6. Single‐channel recordings of the outward currents revealed that the unitary conductance was 130 pS when internal K+ was 131‐143 mM and external K+ was 5 mM. The open probability of the channel showed marked dependence on the membrane potential and the internal Ca2+ concentration. Thus, the current was identified as being Ca2+‐ and membrane potential‐dependent K+ current. 7. Leydig cells within a cluster possessed distinct intercellular couplings. The mean coupling ratio obtained by applying two patch electrodes to a pair of cells was 0.84. Transfer of injected dye (Lucifer Yellow) to adjacent cells was also confirmed. 8. It was concluded that Leydig cells have at least two kinds of voltage‐dependent channels in the membrane. The Ca2+ channel may be activated by physiological changes in membrane potential, leading to an influx of Ca2+. The Ca2+‐dependent K+ channel hardly seems to be activated unless the internal Ca2+ concentration increases remarkably. It is presumed that intercellular coupling may play a role in synchronizing or intensifying the endocrine activities of Leydig cells located within a cluster.
Calcium in biology
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Two-electrode voltage-clamp methodology was used to analyze voltage-dependent ionic conductances in 81 rat hippocampal neurons grown in culture for 4-6 wk. Pyramidal and multipolar cells with 15- to 20-micron-diameter cell bodies were impaled with two independent KCl electrodes. The cells had resting potentials of -30 to -60 mV and an average input resistance of about 30 M omega. A depolarizing command applied to a cell maintained in normal medium invariably evoked a fast (2-10 ms) inward current that saturated the current-passing capacity of the system. This was blocked in a reversible manner by application of tetrodotoxin (TTX) (0.1-1.0 microM) near the recorded cell. In the presence of TTX, a depolarizing command evoked a rapidly rising (3-5 ms), rapidly decaying (25 ms) transient outward current reminiscent of "IA" reported in molluscan neurons. This was followed by a more slowly activating (approximately 100 ms) outward current response of greater amplitude that decayed with a time constant of about 2-3 s. These properties resemble those associated with the K+ conductance, IK, underlying delayed rectification described in many excitable membranes. IK was blocked by extracellular application of tetraethylammonium (TEA) but was insensitive to 4-aminopyridine (4-AP) at concentrations that effectively eliminated IA. IA, in turn, was only marginally depressed by TEA. Unlike IK, IA was completely inactivated when the membrane was held at potentials positive to -50 mV. Inactivation was completely removed by conditioning hyperpolarization at -90 mV. A brief hyperpolarizing pulse (10 ms) was sufficient to remove 95% of the inactivation. IA activated on commands to potentials more positive than -50 mV. The inversion potential of the ionic conductance underlying IA and IK was in the range of the K+ equilibrium potential, EK, as measured by the inversion of tail currents; and this potential was shifted in a depolarizing direction by elevated [K+]0. Thus, both current species reflect activation of membrane conductance to K+ ions. Hyperpolarizing commands from resting potentials revealed a time- and voltage-dependent slowly developing inward current in the majority of cells studied. This membrane current was observed in cells exhibiting "anomalous rectification" and was therefore labeled IAR. It was activated at potentials negative to -70 mV with a time constant of 100-200 ms and was not inactivated. A return to resting potential revealed a tail current that disappeared at about EK. IAR was blocked by extracellular CS+ and was enhanced by elevating [K+]0. It thus appears to be carried by inward movement of K+ ions.(ABSTRACT TRUNCATED AT 400 WORDS)
Tetrodotoxin
Tetraethylammonium
Hyperpolarization
Reversal potential
4-Aminopyridine
Current clamp
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Lobster muscle fibers develop hyperpolarizing responses when subjected to sufficiently strong hyperpolarizing currents. In contrast to axons of frog, toad, and squid, the muscle fibers produce their responses without the need for prior depolarization in high external K(+). Responses begin at a threshold polarization (50 to 70 mv), the potential reaching 150 to 200 mv hyperpolarization while the current remains constant. The increased polarization develops at first slowly, then becomes rapid. It usually subsides from its peak spontaneously, falling temporarily to a potential less hyperpolarized than at threshold for the response. As long as current is applied there can be oscillatory behavior with sequential rise and subsidence of the polarization, repeating a number of times. Withdrawal of current leads to rapid return of the potential to the resting level and a small, brief depolarization. Associated with the latter, but of longer duration, is an increased conductance whose magnitude and duration increase with the antecedent current. Hyperpolarizing responses of lobster muscle fibers are due to increased membrane resistance caused by hyperpolarizing K inactivation. The oscillatory characteristic of the response is due to a delayed superimposed and prolonged increase in membrane permeability, probably for Na(+) and for either K(+) or Cl(-). The hyperpolarizing responses of other tissues also appear to result from hyperpolarizing K inactivation, on which is superimposed an increased conductance for some other ion or ions.
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Spike potential
Reversal potential
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