scholarly journals Multiple Serotonin-Activated Currents in Isolated, Neuronal Somata from Locust Thoracic Ganglia

1992 ◽  
Vol 165 (1) ◽  
pp. 43-60 ◽  
Author(s):  
ISABEL BERMUDEZ ◽  
DAVID J. BEADLE ◽  
JACK A. BENSON
Keyword(s):  
Membrane Potential ◽  
Potassium Conductance ◽  
Membrane Conductance ◽  
Membrane Potentials ◽  
Potential Range ◽  
Neuronal Somata ◽  
Sodium Permeability ◽  
Fast Kinetics ◽  
Thoracic Ganglia ◽  
Slow Kinetics

1. Three different responses were evoked by pressure micro-application of serotonin onto freshly dissociated, current- and voltage-clamped neuronal somata from the thoracic ganglia of the locust Locusta migratoria. 2. In some neurones, an inward current, I(5HT)K, resulting from a decrease in potassium conductance, with slow kinetics and maximum activation at membrane potentials of −60 to - 70 mV, was evoked by serotonin and by the 5-HT3 agonist 2-methyl serotonin. This current was completely abolished by either 10 mmoll−1 caesium or 5 mmoll−1 rubidium and partially blocked by 50 mmoll−1 tetraethylammonium or 5 mmoll−1 4-aminopyridine. The response was antagonised by the 5-HT2-specific compounds, ketanserin and ritanserin. 3. In other somata, serotonin, 2-methyl serotonin and the 5-HT3 antagonist ICS205 930 evoked a second current, I(5HT)Na, which was due to an increase in sodium permeability and had slow kinetics similar to that of I(5HT)K. This current was inward over the membrane potential range −30 to - 80 mV and increased with hyperpolarisation. The response was blocked by sodium-free saline and the 5-HT3 receptor antagonist MDL 72222. 4. In other neurones, at membrane potentials more positive than - 50 mV, serotonin pulses could activate a third current, I(5HT)X, which increased with depolarisation of the membrane potential and had comparatively fast kinetics. Activation of the current was accompanied by a decrease in membrane conductance. This response was completely blocked by 4-aminopyridine and weakly inhibited by both caesium and tetraethylammonium and is, therefore, probably a potassium current. 5. The three currents described here differ in their pharmacology, their ionic mechanisms and their dependence on membrane potential from the serotoninactivated currents reported for vertebrates and they provide evidence for the mechanism of action of serotonin as a neurotransmitter in insects. Note: Present address: Pharmacology Institute, University of Zurich, Gloriastrasse 32, CH-8006 Zurich, Switzerland.

scholarly journals The Influence of External Potassium on the Inactivation of Sodium Currents in the Giant Axon of the Squid, Loligo pealei

1969 ◽  
Vol 53 (6) ◽  
pp. 685-703 ◽  
Author(s):  
William J. Adelman ◽  
Yoram Palti
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Membrane Conductance ◽  
Absolute Magnitude ◽  
Giant Axon ◽  
Membrane Potentials ◽  
Initial Transient ◽  
External Potassium ◽  
Loligo Pealei ◽  
External K

Isolated giant axons were voltage-clamped in seawater solutions having constant sodium concentrations of 230 mM and variable potassium concentrations of from zero to 210 mM. The inactivation of the initial transient membrane current normally carried by Na+ was studied by measuring the Hodgkin-Huxley h parameter as a function of time. It was found that h reaches a steady-state value within 30 msec in all solutions. The values of h∞, τh, αh,and ßh as functions of membrane potential were determined for various [Ko]. The steady-state values of the h parameter were found to be inversely related, while the time constant, τh, was directly related to external K+ concentration. While the absolute magnitude as well as the slopes of the h∞ vs. membrane potential curves were altered by varying external K+, only the magnitude and not the shape of the corresponding τh curves was altered. Values of the two rate constants, αh and ßh, were calculated from h∞ and τh values. αh is inversely related to [Ko] while ßh is directly related to [Ko] for hyperpolarizing membrane potentials and is independent of [Ko] for depolarizing membrane potentials. Hodgkin-Huxley equations relating αh and ßh to Em were rewritten so as to account for the observed effects of [Ko]. It is concluded that external potassium ions have an inactivating effect on the initial transient membrane conductance which cannot be explained solely on the basis of potassium membrane depolarization.

scholarly journals K Permeability of Nitella clavata in the Depolarized State

1973 ◽  
Vol 62 (5) ◽  
pp. 535-549 ◽  
Author(s):  
Hiroshi Kitasato
Keyword(s):  
Membrane Potential ◽  
Finite Number ◽  
Potassium Conductance ◽  
Membrane Potentials ◽  
Membrane Current ◽  
Half Maximum ◽  
Membrane Potential Change ◽  
Potassium Permeability ◽  
Maximum Value ◽  
K Permeability

Membrane current responses to sudden potential changes were recorded in solutions of various [K]o on 52 internodal cells of Nitella clavata. The membrane current after sudden depolarization had a component sensitive to [K]o which increased with time from 0.3 to 2.0 s and remained steady thereafter. This late current became zero at values of E and [K]o which suggests that the current was nearly all carried by K+. The potassium conductivity represented by this current increased with depolarization, with a half-maximum value at about -70 mV, and saturation at about -30 to -20 mV. The potassium conductance also increased with increasing [K]o, but less rapidly than predicted for constant potassium permeability. This failure of the conductance to increase with [K]o was relatively the same at all membrane potentials and may be explained by a model with a finite number of channels. No attempt was made to model the dependence of gK on time after depolarization or on membrane potential. However, the finding that the membrane potential did not affect the way in which the permeability depended on [K]o suggests that the membrane potential change does not affect the affinity of the sites, and that the increase in gK with time after depolarization is brought about by an increase in the number of channels with such sites.

Development of membrane conductance of chick skeletal muscle in culture

1980 ◽  
Vol 58 (6) ◽  
pp. 600-605 ◽  
Author(s):  
C. M. Thomson ◽  
W. F. Dryden
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Initial Level ◽  
Potassium Conductance ◽  
Membrane Conductance ◽  
Resting Membrane Potential ◽  
Membrane Conductances ◽  
Rapid Changes ◽  
Fibre Development

Resting membrane potentials and membrane conductances of chick skeletal muscle in culture were determined from the 3rd to the 10th day after plating. The effect of tetraethylammonium (TEA) and of replacement of potassium with caesium on these parameters was investigated. Resting membrane potential (Em) rises during myogenesis in vitro and resting membrane conductance (Gm) falls. The initial level of Gm was relatively high (1.2 mS cm−2) but this fell to a final level around 0.2 mS cm−2. The most rapid changes in both parameters occurred between days 3 and 5 of culture. Both TEA and caesium depressed Em and Gm at all stages of development. On the 3rd day of culture Gm was reduced by 0.2 mS cm−2 by both agents. Thereafter, Gm was depressed by about 0.1 mS cm−2. Caesium does not penetrate potassium channels and the reduction in Gm is attributed to block of these channels. This indicates that resting potassium conductance is relatively constant at 0.1 mS cm−2 throughout muscle fibre development. Because TEA produces changes in Gm similar to those produced by caesium, TEA is concluded to be acting at the potassium channel in a manner similar to caesium.

Potassium channel family in giant motor axons of Aglantha digitale

1993 ◽  
Vol 69 (3) ◽  
pp. 894-901 ◽  
Author(s):  
R. W. Meech ◽  
G. O. Mackie
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Permeability Coefficient ◽  
Reversal Potential ◽  
Current Data ◽  
Constant Field ◽  
Motor Axons ◽  
Sodium Permeability ◽  
Fast Kinetics ◽  
Slow Kinetics

1. The simplicity of the jellyfish nervous system makes it an ideal preparation to assess the contributions of different ion channels to behavior. In the giant motor axons of the jellyfish Aglantha digitale, low-threshold spikes elicit slow swimming, whereas escape swimming depends on a higher-threshold, overshooting sodium-dependent action potential. At least three kinetically distinct transient potassium channels (fast, intermediate, and slow) are concerned with spike management in this preparation. 2. In situ recording with patch-clamp micropipettes from clusters of potassium channels provides a means of studying their properties in isolation. The three classes of ion channel were identified in ensemble current averages by their kinetics, their response to a conditioning prepulse and their voltage dependence. All three were highly selective for potassium, and the reversal potential of their unitary currents depended on the level of potassium used to fill the patch pipette. 3. A single potassium permeability coefficient (PK) calculated from the Goldman, Hodgkin, Katz “constant field” equation was used to fit unitary current data from all three channels in concentrations of external potassium < or = 500 mM. 4. Data from ensemble tail currents in seawater indicated that the sodium permeability coefficient (PNa) of channels with either intermediate or slow kinetics was < or = 0.015 PK; preliminary data from channels with fast kinetics suggested that they too had a PNa/PK selectivity of approximately 0.01. 5. We propose that spike management in the giant motor axons of Aglantha depends on three members of a family of potassium-selective ion channels that seem likely to be structurally related.

Electrophysiological Pharmacology of the Nicotinic and Muscarinic Cholinergic Responses of Isolated Neuronal Somata from Locust Thoracic Ganglia

1992 ◽  
Vol 170 (1) ◽  
pp. 203-233 ◽  
Author(s):  
JACK A. BENSON
Keyword(s):  
Locusta Migratoria ◽  
Reversal Potential ◽  
Membrane Resistance ◽  
Potential Range ◽  
Neuronal Somata ◽  
Thoracic Ganglia ◽  
Muscarinic Cholinergic ◽  
High Concentrations ◽  
Gallamine Triethiodide

1. Mechanically isolated neuronal somata from the thoracic ganglia of the locust Locusta migratoria remain electrophysiologically viable under current- or voltage-clamp in vitro for many hours. Nicotine and muscarine evoke different responses when pressure-microapplied to these somata. The response to acetylcholine is mainly nicotinic but contains a small muscarinic component. 2. The nicotinic (ACh1) response is a rapid depolarisation accompanied by a decrease in membrane resistance. In voltage-clamped somata, the current mediating the ACh1 response is inward over the membrane potential range −30 to −110 mV, decreasing with depolarisation and with a projected reversal potential of about +20 mV. 3. The muscarinic (ACh2) response is a slow depolarisation accompanied by a decrease in membrane resistance. In voltage-clamped somata, the current mediating the ACh2 response is inward, decreasing to zero at potentials of −80 to −90 mV. 4. The ACh1 response is evoked by nicotine, anabasine, tetramethylammonium, DMPP and relatively high concentrations of the nitromethylene heterocycle insecticide, PMNI. Suberyldicholine or decamethonium evoke the response only when acetylcholine is present in the bathing saline. Nicotinic antagonists of the ACh1 response, in descending order of potency, are PMN1 &gt;&gt; α-bungarotoxin ≥ lobeline≥mecamylamine&gt;trimethaphan camsylate&gt;chlorisondamine&gt;d-tubocurarine≥hexamethomium≥gallamine triethiodide≥tetraethylammonium. This response is also potently blocked by strychnine and more weakly blocked by δ-philanthotoxin, bicuculline and picrotoxin. 5. The ACh2 response is evoked by muscarine, oxotremorine, arecoline, pilocarpine and, very weakly, by the M1-selective agonist McN-A-343. Muscarinic antagonists of the ACh2 response, in descending order of potency, are QNB≥scopolamine&gt;atropine&gt;4-DAMP (M3)≥benactyzine≥HHSiD (M1/M3)≥ pirenzepine (M1). QNX (M1), AF-DX116 (M2), gallamine triethiodide (M2) and methoctramine (M2) are almost or completely inactive.

The effects of L-glutamate and its analogues upon the membrane conductance of central murine neurones in culture

1982 ◽  
Vol 60 (3) ◽  
pp. 282-296 ◽  
Author(s):  
J. F. MacDonald ◽  
J. M. Wojtowicz
Keyword(s):  
Amino Acids ◽  
Membrane Potential ◽  
Divalent Cations ◽  
Potassium Conductance ◽  
Membrane Conductance ◽  
Multiple Receptors ◽  
Voltage Dependent ◽  
Apparent Decrease ◽  
Brain And Spinal Cord ◽  
Related Compounds

Neurones from brain and spinal cord of foetal mice were grown dissociated in monolayer cultures for 4–6 weeks prior to electropharmacological analysis. Neurones were immersed in a Hanks balanced salt solution while drugs and ions were applied by pressure microperfusion during intracellular recordings obtained by conventional techniques. L-Glutamate and its analogues, L-aspartate, DL-homocysteate, N-methyl-D-aspartate, and DL-ibotenate activated two distinct mechanisms of excitation. The primary effect was depolarization accomplished by an apparent decrease of neurone input conductance (Gm). However, in most instances an expected increase in Gm was also observed, especially if membrane potential was reduced by tonic depolarization. Another glutamate analogue, DL-kainate, never decreased Gm and invariably increased Gm at all membrane potentials tested. The decrease of Gm evoked by glutamate and related compounds was strongly dependent upon membrane potential. It was most pronounced at potentials near resting values (−40 to −60 mV) and diminished both with depolarization or hyperpolarization from this range. This apparent decrease favoured the electrogenesis of regenerative potentials that were insensitive to tetrodotoxin. A voltage-dependent increase in sodium and(or) calcium conductance (GNa, GCa) or a decrease in potassium conductance (GK) is suggested to account for this decrease in Gm. Divalent cations (Mg and Co) reduced the depolarizing actions of all amino acids except for those to kainate. The decrease in Gm was more sensitive to Mg than was the increase of Gm. However, the receptor antagonist DL-α-aminoadipate blocked both changes in conductance and responses to all amino acids with the exception of those to kainate. The possible existence of multiple receptors for glutamate is also discussed.

Rat hippocampal astrocytes exhibit electrogenic sodium-bicarbonate co-transport

1994 ◽  
Vol 72 (6) ◽  
pp. 2580-2589 ◽  
Author(s):  
E. R. O'Connor ◽  
H. Sontheimer ◽  
B. R. Ransom
Keyword(s):  
Membrane Potential ◽  
Reversal Potential ◽  
Input Resistance ◽  
Membrane Potentials ◽  
Resting Membrane Potential ◽  
Induced Response ◽  
Potential Range ◽  
Free Solution ◽  
Hippocampal Astrocytes ◽  
In Cells

1. We probed for the expression of electrogenic Na+/HCO3- co-transport in cultured mammalian astrocytes by recording voltage and current changes induced by bath application of HCO3-, with the use of patch-clamp electrophysiology. Application of 25 mM HCO3-, at a constant pHo, to astrocytes bathed in a nominally HCO3(-)-free solution, produced an abrupt and reversible change in membrane potential ranging from +3 to -30 mV [-11.8 +/- 9.34 (SD) mV]; 55% of cells showed relatively large hyperpolarizing responses (-18.8 +/- 6.23 mV), whereas 45% showed only small shifts in membrane potential (range of -5 to +3 mV; -1.9 +/- 1.96 mV). 2. The size of the HCO3(-)-induced hyperpolarization was strongly related to the cell's initial resting membrane potential in HCO3(-)-free solution; the larger responses were seen in cells with relatively low resting membrane potentials (-48.5 +/- 9.4 mV), and the smaller responses were seen in cells with more negative potentials (-68.1 +/- 6.5 mV). The membrane potentials of hippocampal astrocytes were highly variable in HCO3(-)-free solution (range -38 to -80 mV; -60.9 +/- 12.53); this variability was greatly reduced in HCO3(-)-containing solution (range -59 to -82 mV; -68.5 +/- 4.8). 3. The magnitude of the HCO3(-)-induced response was less strongly correlated with cell input resistance, which was higher in the larger responder cells than in the small responders. However, the differences in input resistance were insufficient to account for the different HCO3(-)-induced responses observed. 4. In the presence of extracellular Ba2+, which by blocking K+ conductance depolarized cells by 30-50 mV, cells that initially showed a small response, showed a large and completely reversible hyperpolarization (-18.4 +/- 6.13 mV) to application of 25 mM HCO3-. In Na(+)-free solution, the HCO3(-)-induced hyperpolarization was reduced by 66%, and the response was not sustained, as in Na(+)-containing solution. Removal of extracellular Cl- had no effect on the HCO3- response The stilbene derivative 4,4'-diisothiocyano-2,2'-stilbene disulfonate (DIDS), a blocker of anion transport, eliminated the HCO3(-)-induced hyperpolarization. Blockers of Na+/K+ ATPase and Na(+)-H+ exchange were without effect. These observations indicated the presence of an electrogenic Na+/HCO3- co-transporter in hippocampal astrocytes. 6. Voltage-clamp recording demonstrated that the HCO3(-)-induced hyperpolarization was caused by outward currents averaging 335 +/- 104 pA. The reversal potential of the HCO3(-)-induced current ranged between -80 and -99 mV with an average = -86.1 +/- 6.2 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Frequency-dependent amplification of stretch-evoked excitatory input in spinal motoneurons

2012 ◽  
Vol 108 (3) ◽  
pp. 753-759 ◽  
Author(s):  
Randall K. Powers ◽  
Paul Nardelli ◽  
T. C. Cope
Keyword(s):  
Membrane Potential ◽  
Low Frequency ◽  
Excitatory Input ◽  
Medial Gastrocnemius ◽  
Frequency Dependent ◽  
Fast Kinetics ◽  
Synaptic Inputs ◽  
Slow Kinetics ◽  
Voltage Dependent ◽  
Inward Currents

Voltage-dependent calcium and sodium channels mediating persistent inward currents (PICs) amplify the effects of synaptic inputs on the membrane potential and firing rate of motoneurons. CaPIC channels are thought to be relatively slow, whereas the NaPIC channels have fast kinetics. These different characteristics influence how synaptic inputs with different frequency content are amplified; the slow kinetics of Ca channels suggest that they can only contribute to amplification of low frequency inputs (<5 Hz). To characterize frequency-dependent amplification of excitatory postsynaptic potentials (EPSPs), we measured the averaged stretch-evoked EPSPs in cat medial gastrocnemius motoneurons in decerebrate cats at different subthreshold levels of membrane potential. EPSPs were produced by muscle spindle afferents activated by stretching the homonymous and synergist muscles at frequencies of 5–50 Hz. We adjusted the stretch amplitudes at different frequencies to produce approximately the same peak-to-peak EPSP amplitude and quantified the amount of amplification by expressing the EPSP integral at different levels of depolarization as a percentage of that measured with the membrane hyperpolarized. Amplification was observed at all stretch frequencies but generally decreased with increasing stretch frequency. However, in many cells the amount of amplification was greater at 10 Hz than at 5 Hz. Fast amplification was generally reduced or absent when the lidocaine derivative QX-314 was included in the electrode solution, supporting a strong contribution from Na channels. These results suggest that NaPICs can combine with CaPICs to enhance motoneuron responses to modulations of synaptic drive over a physiologically significant range of frequencies.

scholarly journals On the Wireless Microwave Sensing of Bacterial Membrane Potential in Microfluidic-Actuated Platforms

Sensors ◽  
2021 ◽  
Vol 21 (10) ◽  
pp. 3420
Author(s):  
Marc Jofre ◽  
Lluís Jofre ◽  
Luis Jofre-Roca
Keyword(s):  
Membrane Potential ◽  
Living Cells ◽  
Membrane Potentials ◽  
Electromagnetic Properties ◽  
Bacterial Membrane ◽  
Microfluidic Platforms ◽  
Bacterial Membranes ◽  
Wireless Monitoring ◽  
Bacterial Dynamics ◽  
Engineered Systems

The investigation of the electromagnetic properties of biological particles in microfluidic platforms may enable microwave wireless monitoring and interaction with the functional activity of microorganisms. Of high relevance are the action and membrane potentials as they are some of the most important parameters of living cells. In particular, the complex mechanisms of a cell’s action potential are comparable to the dynamics of bacterial membranes, and consequently focusing on the latter provides a simplified framework for advancing the current techniques and knowledge of general bacterial dynamics. In this work, we provide a theoretical analysis and experimental results on the microwave detection of microorganisms within a microfluidic-based platform for sensing the membrane potential of bacteria. The results further advance the state of microwave bacteria sensing and microfluidic control and their implications for measuring and interacting with cells and their membrane potentials, which is of great importance for developing new biotechnologically engineered systems and solutions.

Inward rectification in rat nucleus accumbens neurons

1989 ◽  
Vol 62 (6) ◽  
pp. 1280-1286 ◽  
Author(s):  
N. Uchimura ◽  
E. Cherubini ◽  
R. A. North
Keyword(s):  
Steady State ◽  
Nucleus Accumbens ◽  
Time Course ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Inward Rectification ◽  
Resting Membrane Potential ◽  
Potential Range ◽  
Inward Current ◽  
Rat Nucleus Accumbens

1. Intracellular recordings were made from neurons in slices cut from the rat nucleus accumbens septi. Membrane currents were measured with a single-electrode voltage-clamp amplifier in the potential range -50 to -140 mV. 2. In control conditions (2.5 mM potassium), the resting membrane potential of the neurons was -83.4 +/- 1.1 (SE) mV (n = 157). Steady state membrane conductance was voltage dependent, being 34.8 +/- 1.7 nS (n = 25) at -100 mV and 8.0 +/- 0.7 nS (n = 25) at -60 mV. 3. Barium (1 microM) markedly reduced the inward rectification and caused a small inward current (40.6 +/- 8.7 pA, n = 8) at the resting potential. These effects became larger with higher barium concentrations, and, in 100 microM barium, the current-voltage relation was straight. 4. The block of the inward current by barium (at -130 mV) occurred with an exponential time course; the time constant was approximately 1 s at 1 microM barium and less than 90 ms with 100 microM. Strontium had effects similar to those of barium, but 1000-fold higher concentrations were required. Cesium chloride (2 mM) and rubidium chloride (2 mM) also blocked the inward rectification; their action reached steady state within 50 ms. 5. It is concluded that the nucleus accumbens neurons have a potassium conductance with many features of a typical inward rectifier and that this contributes to the potassium conductance at the resting potential.

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