Evidence for Ca2+-activated K+ Conductance in Cat Spinal Motoneurons from Intracellular EGTA Injections

1975 ◽  
Vol 53 (6) ◽  
pp. 1214-1218 ◽  
Author(s):  
K. Krnjević ◽  
E. Puil ◽  
R. Werman
Keyword(s):  
Ethylene Glycol ◽  
Action Potential ◽  
Significant Role ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Tetraacetic Acid ◽  
Spinal Motoneurons ◽  
Repolarization Phase

Ethylene glycol bis-(β-aminoelhyl ether)-N,N′-tetraacetic acid, injected by iontophoresis from triple-barrelled intracellular micropipettes, consistently raised the membrane resistance and depressed the post-spike after hyperpolarization (AHP), but did not slow the falling phase of the action potential. [Ca2+]i-activated K+ channels appear to play a significant role in the genesis of the AHP and in the control of the resting potential, but not in the repolarization phase of the action potential.

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.

Effect of sodium deficiency of the action potential of the smooth muscle of ureter

1964 ◽  
Vol 206 (1) ◽  
pp. 205-210 ◽  
Author(s):  
Makoto Kobayashi ◽  
Hiroshi Irisawa
Keyword(s):  
Smooth Muscle ◽  
Action Potential ◽  
Action Potentials ◽  
Essential Role ◽  
Choline Chloride ◽  
Resting Potential ◽  
Sodium Deficiency ◽  
Repolarization Phase ◽  
Extracellular Sodium

Action potentials of the smooth muscle of cat ureter were studied by using ultramicroelectrodes. Among 193 penetrations, the resting potential averaged 45 mv and the amplitude of action potential 32 mv. In four instances a slight overshoot was recorded. Action potential consisted of a relatively rapid rising phase followed by a slow repolarization phase, and its duration was about 0.3 sec. Effects of sodium deficiency on action potential were studied by using three different sodium substitutes. Both the height and the rising rate of action potential decreased as the concentration of extracellular sodium was reduced, indicating that the action potential of ureter muscle can be explained on the basis of sodium theory. The duration of the action potential was prolonged when sucrose or choline chloride was used as a sodium substitute; on the other hand, it shortened when tris chloride was employed. The essential role of sodium ions in the development of the action potential in ureter muscle is discussed.

Electrophysiological characterization of single pregnant rat myometrial cells in short-term primary culture

1986 ◽  
Vol 250 (1) ◽  
pp. C47-C54 ◽  
Author(s):  
P. Mollard ◽  
J. Mironneau ◽  
T. Amedee ◽  
C. Mironneau
Keyword(s):  
Action Potential ◽  
Primary Culture ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Short Term ◽  
Pregnant Rat ◽  
Myometrial Cells ◽  
The Mean ◽  
Electrophysiological Characterization ◽  
Specific Membrane

Smooth muscle cells were isolated from the longitudinal layer of pregnant rat myometrium (18-19 days) and studied either freshly dissociated or during short-term primary culture (until 30 h) using intracellular microelectrode techniques and direct microscopic observation. The isolated myometrial cells excluded trypan blue vital stain and could repetitively contract in response to various stimuli. Electrophysiological studies at 37 degrees C showed normal resting potential (-54.5 +/- 7.5 mV, n = 71). Action potentials with overshoot (+7.8 +/- 4.6 mV, n = 71) could be elicited by intracellular stimulation. Moreover, the membrane potential was largely dependent on the external K+ concentration. The action potential was suppressed in a Ca2+-free solution [with 0.1 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid], and the overshoot amplitude was clearly Ca2+ dependent. The action potential was inhibited by Mn2+ ions (1 mM), Co2+ ions (1 mM), and D 600 (1 microM) but was unaffected by tetrodotoxin (2 microM) and external Na+ removal. Tetraethylammonium chloride (TEA, 10 mM) and 4-aminopyridine (4-AP, 10 mM) increased both overshoot amplitude and duration of the electrical responses. When the cell surface area was measured with light microscopy, the mean specific membrane resistance was 14.8 +/- 4.6 k omega . cm2 (n = 14), and the mean specific membrane capacitance was 2.3 +/- 0.7 microF/cm2 (n = 14). Outward-going rectification was consistently observed in all cells examined. This was either inhibited by TEA and 4-AP (10 mM each) or reduced in the presence of 1 mM Mn2+.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals DEMONSTRATION OF TWO STABLE POTENTIAL STATES IN THE SQUID GIANT AXON UNDER TETRAETHYLAMMONIUM CHLORIDE

1957 ◽  
Vol 40 (6) ◽  
pp. 859-885 ◽  
Author(s):  
Ichiji Tasaki ◽  
Susumu Hagiwara
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Membrane Conductance ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Squid Giant Axon ◽  
Resting Potential ◽  
Unstable State ◽  
Stable States ◽  
Tetraethylammonium Chloride

1. Intracellular injection of tetraethylammonium chloride (TEA) into a giant axon of the squid prolongs the duration of the action potential without changing the resting potential (Fig. 3). The prolongation is sometimes 100-fold or more. 2. The action potential of a giant axon treated with TEA has an initial peak followed by a plateau (Fig. 3). The membrane resistance during the plateau is practically normal (Fig. 4). Near the end of the action potential, there is an apparent increase in the membrane resistance (Fig. 5D and Fig. 6, right). 3. The phenomenon of abolition of action potentials was demonstrated in the squid giant axon treated with TEA (Fig. 7). Following an action potential abolished in its early phase, there is no refractoriness (Fig. 8). 4. By the method of voltage clamp, the voltage-current relation was investigated on normal squid axons as well as on axons treated with TEA (Figs. 9 and 10). 5. The presence of stable states of the membrane was demonstrated by clamping the membrane potential with two voltage steps (Fig. 11). Experimental evidence was presented showing that, in an "unstable" state, the membrane conductance is not uniquely determined by the membrane potential. 6. The effect of low sodium water was investigated in the axon treated with TEA (Fig. 12). 7. The similarity between the action potential of a squid axon under TEA and that of the vertebrate cardiac muscle was stressed. The experimental results were interpreted as supporting the view that there are two stable states in the membrane. Initiation and abolition of an action potential were explained as transitions between the two states.

scholarly journals On the effects of divalent cations and ethylene glycol-bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetate on action potential duration in frog heart.

1978 ◽  
Vol 71 (1) ◽  
pp. 47-67 ◽  
Author(s):  
D J Miller ◽  
A Mörchen
Keyword(s):  
Ethylene Glycol ◽  
Action Potential ◽  
Calcium Ions ◽  
Action Potentials ◽  
Time Course ◽  
Divalent Cations ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Slow Inward Current ◽  
Frog Heart

Resting and action potentials were recorded from superfused strips of frog ventricle. Reducing the bathing calcium concentration ([Ca2+]0) with or without ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA) prolongs the action potential (AP). The change in the duration of the AP extends over many minutes, but is rapidly reversed by restoring calcium ions. Other changes (e.g., in resting potential and overshoot) are, however, only more slowly reversed. Reducing [Ca2+]0 with 0.2, 2, or 5 mM EGTA produces progressively greater prolongation of AP; maximum values were well in excess of 1 min. This prolongation can be reversed by other divalent cations in EGTA (Mg2+, Sr2+) or Ca-free (Mn2+) solutions, or by acetylcholine. Barium ions increase AP duration in keeping with their known effect on potassium conductance. D600, which blocks the slow inward current in cardiac muscle, is without effect on the action potentials recorded in EGTA solutions, or on the time course and extent of the recovery to normal duration upon restoring calcium ions. It is concluded that divalent cations exert an influence on membrane potassium conductance extracellularly in frog heart. The cell membrane does not become excessively "leaky" in EGTA solutions.

Hyperexcitability of Cultured Spinal Motoneurons From Presymptomatic ALS Mice

2004 ◽  
Vol 91 (1) ◽  
pp. 571-575 ◽  
Author(s):  
Jason J. Kuo ◽  
Martijn Schonewille ◽  
Teepu Siddique ◽  
Annet N. A. Schults ◽  
Ronggen Fu ◽  
...  
Keyword(s):  
Action Potential ◽  
Firing Frequency ◽  
Resting Potential ◽  
Spinal Motoneurons ◽  
Electrophysiological Properties ◽  
Potential Shape ◽  
Wide Range ◽  
Action Potential Shape ◽  
And Control ◽  
The Relationship

ALS (amyotrophic lateral sclerosis) is an adult-onset and deadly neurodegenerative disease characterized by a progressive and selective loss of motoneurons. Transgenic mice overexpressing a mutated human gene (G93A) coding for the enzyme SOD1 (Cu/Zn superoxide dismutase) develop a motoneuron disease resembling ALS in humans. In this generally accepted ALS model, we tested the electrophysiological properties of individual embryonic and neonatal spinal motoneurons in culture by measuring a wide range of electrical properties influencing motoneuron excitability during current clamp. There were no differences in the motoneuron resting potential, input conductance, action potential shape, or afterhyperpolarization between G93A and control motoneurons. The relationship between the motoneuron's firing frequency and injected current (f-I relation) was altered. The slope of the f-I relation and the maximal firing rate of the G93A motoneurons were much greater than in the control motoneurons. Differences in spontaneous synaptic input were excluded as a cause of increased excitability. This finding identifies a markedly elevated intrinsic electrical excitability in cultured embryonic and neonatal mutant G93A spinal motoneurons. We conclude that the observed intrinsic motoneuron hyperexcitability is induced by the SOD1 toxic gain-of-function through an aberration in the process of action potential generation. This hyperexcitability may play a crucial role in the pathogenesis of ALS as the motoneurons were cultured from presymptomatic mice.

scholarly journals THE EFFECTS OF HYDROSTATIC PRESSURE UPON THE NORMAL AND NARCOTIZED NERVE FIBER

1957 ◽  
Vol 40 (6) ◽  
pp. 849-857 ◽  
Author(s):  
Constantine S. Spyropoulos
Keyword(s):  
Action Potential ◽  
Nerve Fiber ◽  
Low Temperatures ◽  
High Pressures ◽  
Giant Axon ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Impedance Change ◽  
Membrane Capacity ◽  
Membrane Impedance

The properties of the giant axon of the squid Loligo pealii were studied at different hydrostatic pressures from 14.7 to 16,000 psi. At 4000 psi the resting potential, the membrane resistance, membrane capacity, the conduction velocity, the amplitude of the action potential, and the maximal change in the membrane impedance during activity were only slightly affected. At the same pressure the duration of the falling phase of the action potential was increased by about 40 to 60 per cent and the duration of the rising phase by about 20 to 35 per cent. The duration of the membrane impedance change during activity was increased by 50 to 100 per cent at 4000 psi. At pressures even slightly above atmospheric the threshold membrane current was appreciably reduced. At about 3000 to 7000 psi the fiber fired spontaneously. At pressures considerably above 5000 psi the membrane resistance decreased to about one-half to one-third the original value. The narcotizing effect upon the nerve fiber of 3 to 7 per cent ethanol was partly or almost completely opposed by low temperatures or high pressures.

Is cyclic guanosine monophosphate the internal 'second messenger' for cholinergic actions on central neurons?

1976 ◽  
Vol 54 (2) ◽  
pp. 172-176 ◽  
Author(s):  
K. Krnjević ◽  
E. Puil ◽  
R. Werman
Keyword(s):  
Time Course ◽  
Membrane Conductance ◽  
Cyclic Guanosine Monophosphate ◽  
Guanosine Monophosphate ◽  
Resting Potential ◽  
Electrical Excitability ◽  
Spinal Motoneurons ◽  
Central Neurons ◽  
Intracellular Cgmp ◽  
Post Synaptic Potential

The most consistent effects produced by intracellular injections of guanosine 3′,5′-cyclic monophosphate (cGMP) (but not 5′-guanosine 5′-monophosphate in spinal motoneurons of cats are a rise in membrane conductance, acceleration in time course of spike potentials, and accentuation of the post-spike hyperpolarization. Associated changes in resting potential are smaller, less constant, and more often in the depolarizing than hyperpolarizing direction. cGMP tends to increase electrical excitability but reduces excitatory post-synaptic potential amplitudes. Most of the effects of intracellular cGMP are quite different from, or indeed opposite to, those of either extra- or intracellular applications of acetylcholine and therefore not consistent with the proposal that cGMP is the internal mediator of muscarinic actions.

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