Cyclic nucleotides in spinal cells

1976 ◽  
Vol 54 (3) ◽  
pp. 416-421 ◽  
Author(s):  
K. Krnjevic ◽  
W. G. Van Meter
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Cyclic Nucleotides ◽  
Membrane Resistance ◽  
Resting Membrane Potential ◽  
Cyclic Monophosphate ◽  
Synaptic Facilitation ◽  
Marked Enhancement

The most striking effects of intracellular injections of adenosine 3′5′-cyclic monophosphate (cAMP) into spinal mononeurons in cats are a speeding-up of the action potential, both its rising and falling phase, and a potentiation of the after-hyperpolarization; the latter probably indicates a marked enhancement of Ca2+ influx. In this respect, cAMP and guanosine 3′5′-cyclic monophosphate (cGMP) have similar actions, though cAMP appears to be more potent. It is suggested that through this mechanism, cyclic nucleotides may play an important role in synaptic facilitation. Changes in resting membrane potential and resistance are less conspicuous or predictable. By contrast, both agents, when injected into unresponsive cells, presumed to be neuroglia, regularly cause a drop in membrane resistance; this is associated with hyperpolarization and therefore likely to reflect an increase in membrane K+ conductance.

scholarly journals The Effect of Aconitine on the Giant Axon of the Squid

1964 ◽  
Vol 47 (4) ◽  
pp. 719-733 ◽  
Author(s):  
W. H. Herzog ◽  
R. M. Feibel ◽  
S. H. Bryant
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Action Potentials ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Repetitive Stimulation ◽  
Resting Membrane Potential ◽  
Sustained Activity ◽  
Frequency Of Stimulation ◽  
Sodium And Potassium

In the giant axon of Loligo pealii, "aconitine potent" Merck added to the bath (10-7 to 1.25 x 10-6 gm/ml) (a) had no effect on resting membrane potential, membrane resistance and rectification, membrane response to subthreshold currents, critical depolarization, or action potential, but (b) on repetitive stimulation produced oscillations of membrane potential after the spike, depolarization, and decrease of membrane resistance. The effect sums with successive action potentials; it increases with concentration of aconitine, time of exposure, and frequency of stimulation. When the oscillations are large enough and the membrane potential is 51.6 ± SD 1.5 mv a burst of self-sustained activity begins; it usually lasts 20 to 70 sec. and at its end the membrane potential is 41.5 ± SD 1.9 mv. Repolarization occurs with a time constant of 2.5 to 11.1 min. Substitution of choline for external sodium after a burst hyperpolarizes the membrane to -70 mv, and return to normal external sodium depolarizes again beyond the resting membrane potential. The effect of aconitine on the membrane is attributed to an increase of sodium and potassium or chloride conductances following the action potential.

Modulation of membrane potential by an acetylcholine-activated potassium current in trout atrial myocytes

2007 ◽  
Vol 292 (1) ◽  
pp. R388-R395 ◽  
Author(s):  
Cristina E. Molina ◽  
Hans Gesser ◽  
Anna Llach ◽  
Lluis Tort ◽  
Leif Hove-Madsen
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Membrane Potentials ◽  
Resting Membrane Potential ◽  
Atrial Myocytes ◽  
Atrial Tissue ◽  
Isolated Cardiac Myocytes ◽  
Inwardly Rectifying

Application of the current-clamp technique in rainbow trout atrial myocytes has yielded resting membrane potentials that are incompatible with normal atrial function. To investigate this paradox, we recorded the whole membrane current ( Im) and compared membrane potentials recorded in isolated cardiac myocytes and multicellular preparations. Atrial tissue and ventricular myocytes had stable resting potentials of −87 ± 2 mV and −83.9 ± 0.4 mV, respectively. In contrast, 50 out of 59 atrial myocytes had unstable depolarized membrane potentials that were sensitive to the holding current. We hypothesized that this is at least partly due to a small slope conductance of Im around the resting membrane potential in atrial myocytes. In accordance with this hypothesis, the slope conductance of Im was about sevenfold smaller in atrial than in ventricular myocytes. Interestingly, ACh increased Im at −120 mV from 4.3 pA/pF to 27 pA/pF with an EC50 of 45 nM in atrial myocytes. Moreover, 3 nM ACh increased the slope conductance of Im fourfold, shifted its reversal potential from −78 ± 3 to −84 ± 3 mV, and stabilized the resting membrane potential at −92 ± 4 mV. ACh also shortened the action potential in both atrial myocytes and tissue, and this effect was antagonized by atropine. When applied alone, atropine prolonged the action potential in atrial tissue but had no effect on membrane potential, action potential, or Im in isolated atrial myocytes. This suggests that ACh-mediated activation of an inwardly rectifying K+ current can modulate the membrane potential in the trout atrial myocytes and stabilize the resting membrane potential.

Effect of aminophylline on the contraction threshold of rat diaphragm fibers

1991 ◽  
Vol 71 (4) ◽  
pp. 1409-1414 ◽  
Author(s):  
A. S. Losavio ◽  
B. A. Kotsias
Keyword(s):  
Membrane Potential ◽  
Sarcoplasmic Reticulum ◽  
Resting Membrane Potential ◽  
Dependent Manner ◽  
Direct Visualization ◽  
Rat Diaphragm ◽  
Current Clamp ◽  
Cyclic Monophosphate ◽  
Dose Dependent

We studied the effect of aminophylline (0.1–1 mM) on the contraction threshold (CT) of rat diaphragm fibers (25 degrees C). The CT was measured by direct visualization (x200) of the fiber under current-clamp conditions. The main findings are the following: 1) Aminophylline lowers the CT, in a dose-dependent manner, toward more negative values of the resting membrane potential (Vm). 2) Dibutyryl adenosine 3′,5′-cyclic monophosphate (2 mM) shifts the CT, although this change is smaller than in the presence of xanthine. 3) Tetracaine (1 mM), a drug that diminishes Ca release from the sarcoplasmic reticulum, reduces the shift induced by 1 mM aminophylline; this is partially overcome by increasing aminophylline concentration to 5 mM. 4) Hyperpolarization of the fibers shifts the CT to more negative Vm. We suggest that the displacement in the CT to more negative Vm plays an important role in the potentiating effect of aminophylline. This could be the result of an enhancement of Ca release from the sarcoplasmic reticulum.

Hormonal Signaling Actions on Kv7.1 (KCNQ1) Channels

2021 ◽  
Vol 61 (1) ◽  
pp. 381-400
Author(s):  
Emely Thompson ◽  
Jodene Eldstrom ◽  
David Fedida
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Cardiac Action Potential ◽  
Resting Membrane Potential ◽  
Voltage Gated ◽  
M Current ◽  
Kv7 Channels ◽  
Cardiac Action ◽  
Repolarization Phase ◽  
And Control

Kv7 channels (Kv7.1–7.5) are voltage-gated K+ channels that can be modulated by five β-subunits (KCNE1–5). Kv7.1-KCNE1 channels produce the slow-delayed rectifying K+ current, IKs, which is important during the repolarization phase of the cardiac action potential. Kv7.2–7.5 are predominantly neuronally expressed and constitute the muscarinic M-current and control the resting membrane potential in neurons. Kv7.1 produces drastically different currents as a result of modulation by KCNE subunits. This flexibility allows the Kv7.1 channel to have many roles depending on location and assembly partners. The pharmacological sensitivity of Kv7.1 channels differs from that of Kv7.2–7.5 and is largely dependent upon the number of β-subunits present in the channel complex. As a result, the development of pharmaceuticals targeting Kv7.1 is problematic. This review discusses the roles and the mechanisms by which different signaling pathways affect Kv7.1 and KCNE channels and could potentially provide different ways of targeting the channel.

scholarly journals Membrane Potentials of the Lobster Giant Axon Obtained by Use of the Sucrose-Gap Technique

1962 ◽  
Vol 45 (6) ◽  
pp. 1195-1216 ◽  
Author(s):  
Fred J. Julian ◽  
John W. Moore ◽  
David E. Goldman
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Sea Water ◽  
Sucrose Solution ◽  
Chloride Concentration ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Gap Technique ◽  
Sucrose Gap

A method similar to the sucrose-gap technique introduced be Stäpfli is described for measuring membrane potential and current in singly lobster giant axons (diameter about 100 micra). The isotonic sucrose solution used to perfuse the gaps raises the external leakage resistance so that the recorded potential is only about 5 per cent less than the actual membrane potential. However, the resting potential of an axon in the sucrose-gap arrangement is increased 20 to 60 mv over that recorded by a conventional micropipette electrode when the entire axon is bathed in sea water. A complete explanation for this effect has not been discovered. The relation between resting potential and external potassium and sodium ion concentrations shows that potassium carries most of the current in a depolarized axon in the sucrose-gap arrangement, but that near the resting potential other ions make significant contributions. Lowering the external chloride concentration decreases the resting potential. Varying the concentration of the sucrose solution has little effect. A study of the impedance changes associated with the action potential shows that the membrane resistance decreases to a minimum at the peak of the spike and returns to near its initial value before repolarization is complete (a normal lobster giant axon action potential does not have an undershoot). Action potentials recorded simultaneously by the sucrose-gap technique and by micropipette electrodes are practically superposable.

Effects of sodium on beta-cell electrical activity

1982 ◽  
Vol 242 (5) ◽  
pp. C296-C303 ◽  
Author(s):  
B. Ribalet ◽  
P. M. Beigelman
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Beta Cell ◽  
Pancreatic Beta Cell ◽  
Input Resistance ◽  
Resting Membrane Potential ◽  
Two Phase ◽  
Sodium Permeability ◽  
Potential Spike ◽  
Presence And Absence

The present studies, designed to evaluate the contribution of Na+ to the mouse pancreatic beta-cell membrane potential, were performed utilizing intracellular microelectrodes. Complete removal of external sodium, in the presence of glucose, did not significantly affect spike peak potential. However, it caused a negative shift of the resting membrane potential, both in the presence and absence of glucose. After this initial hyperpolarization, the membrane gradually depolarized, the rate of depolarization being slower in the absence of glucose. This two-phase hyperpolarization-depolarization pattern remained when ouabain was added, both in the presence and absence of glucose. An increase of input resistance was associated with the slow depolarization. During this depolarization the maximum rate of rise (dV/dtmax) of the action potential (“spike”) decreased. There was no direct relationship between dV/dtmax and [Na]0. Readdition of low [Na]0 (14 mM) to a glucose medium reactivated the postburst hyperpolarization (PBH), even in the presence of ouabain. These observations indicate that there is a significant resting sodium permeability (PNa). However, the action potential (spike) is not generated by activation of a voltage-dependent (gated) sodium channel. The membrane depolarization after Na+ removal reflects concomitant inhibition of the Na+-K+ pump and decrease of potassium permeability (PK). The blockage of PBH in the absence of Na+ is not related to the inhibition of an oscillatory Na+-K+ pump but to the inactivation of a PK. Aside from its effect on the Na+-K+ pump, ouabain may stimulate PNa.

Influence of age and run training on cardiac Na+/Ca2+ exchange

2003 ◽  
Vol 95 (5) ◽  
pp. 1994-2003 ◽  
Author(s):  
Lisa C. Mace ◽  
Bradley M. Palmer ◽  
David A. Brown ◽  
Korinne N. Jew ◽  
Joshua M. Lynch ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Left Ventricular ◽  
Brown Norway ◽  
Resting Membrane Potential ◽  
Whole Cell Patch Clamp ◽  
Age Related ◽  
Intracellular Ca ◽  
Whole Heart ◽  
Exchange Activity

Effects of age and training on myocardial Na+/Ca2+ exchange were examined in young sedentary (YS; 14-15 mo), aged sedentary (AS; 27-31 mo), and aged trained (AT; 8- to 11-wk treadmill run training) male Fischer Brown Norway rats. Whole heart performance and isolated cardiocyte Na+/Ca2+ exchange characteristics were measured. At the whole heart level, a small but significant slowing of late isovolumic left ventricular (LV) relaxation, which may be indicative of altered Na+/Ca2+ exchange activity, was seen in hearts from AS rats. This subtle impairment in relaxation was not observed in hearts from AT rats. At the single-cardiocyte level, late action potential duration was prolonged, resting membrane potential was more positive, and overshoot potential was greater in cardiocytes from AS rats than from YS rats ( P < 0.05). Training did not influence any of these age-related action potential characteristics. In electrically paced cardiocytes, neither shortening nor intracellular Ca2+ concentration ([Ca2+]i) dynamics was influenced by age or training. Similarly, neither age nor training influenced the rate of [Ca2+]i clearance via forward (Nain+ /Caout2+) Na+/Ca2+ exchange after caffeine-induced Ca2+ release from the sarcoplasmic reticulum or cardiac Na+/Ca2+ exchanger protein (NCX1) expression. However, when whole cell patch-clamp techniques combined with fluorescence microscopy were used to evaluate the ability of Na+/Ca2+ exchange to alter cytosolic [Ca2+] ([Ca2+]c) under conditions where membrane potential ( Vm) and internal and external [Na+] and [Ca2+] could be controlled, we observed age-associated increases in forward Na+/Ca2+ exchange-mediated [Ca2+]c clearance ( P < 0.05) that were not influenced by training. The age-related increase in forward Na+/Ca2+ exchange activity provides a hypothetical explanation for the late action potential prolongation observed in this study.

scholarly journals Electrical Characteristics and Activation Potential of Bufo Eggs

1959 ◽  
Vol 43 (1) ◽  
pp. 139-157 ◽  
Author(s):  
Takashi Maéno
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Membrane Resistance ◽  
Chloride Ions ◽  
Potassium Ions ◽  
Ionic Mechanism ◽  
Electrical Characteristics ◽  
Activation Potential ◽  
Specific Permeability ◽  
Toad Bufo

Electrical characteristics and their changes during activation were studied with the microelectrodes on the oocytes and eggs of the toad, Bufo vulgaris formosus Boulenger. In young oocytes, the membrane characteristics had some similarities to those of nerve and muscle, except for a relatively large resistance of 25 KΩcm.2 and an absence of the action potential in the former. After maturation, however, the membrane characteristics became entirely different from those of oocytes and other excitable tissues. In the mature eggs the membrane resistance was measured to be as high as 200 KΩcm.2, and no specific permeability of the membrane to potassium ions was observable. A slow monophasic change in the membrane potential was recorded in every activation produced by mechanical stimulation, and termed "activation potential." In fresh water, its amplitude was as large as 80 to 90 mv. with an overshoot of about 50 mv. The activation potential might be comparable to the action potential of nerve and muscle, but was fundamentally different in ionic mechanism from the latter, since the former was caused by a marked increase in permeability to chloride ions.

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