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.

Voltage-dependent modulation of GABAA receptor channel desensitization in rat hippocampal neurons

1994 ◽  
Vol 71 (6) ◽  
pp. 2151-2160 ◽  
Author(s):  
K. W. Yoon
Keyword(s):  
Membrane Potential ◽  
Hippocampal Neurons ◽  
Membrane Conductance ◽  
Cell Voltage ◽  
Chloride Conductance ◽  
Membrane Voltage ◽  
Hippocampal Cell Culture ◽  
Voltage Dependent ◽  
Agonist Concentration ◽  
Rate Of Recovery

1. The mechanism of the time-dependent decline in gamma-amino-butyric acid (GABA)-induced chloride conductance, referred to as desensitization, was studied in dissociated rat hippocampal cell culture with the use of a whole-cell voltage-clamp recording. 2. In most cells the gradual decline of membrane conductance was dependent simultaneously on the agonist concentration and membrane voltage. Even in the continued presence of GABA, desensitization could be prevented by holding the membrane potential > 0 mV in a near symmetrical chloride gradient across the cell membrane. 3. The “recovery” from desensitization occurred after removal of the agonist with a time constant of approximately 35 s. The rate of recovery from desensitization was independent of membrane voltage. 4. When the membrane potential was jumped from a negative to a positive membrane potential during steady state of desensitization, the GABA-induced chloride conductance gradually “relaxed” to the undesensitized state. This phenomenon of gradual increase in chloride conductance or “reactivation” from desensitization was both voltage and agonist dependent. 5. The process of recovery of the GABA ionophore from the desensitized state is distinct from the process of reactivation, which is dependent both on the voltage and agonist. 6. These observations suggest that the ligand-bound GABA receptor has two alternate states, i.e., permissive (activated) and desensitized. The rates of transition between these two states are voltage dependent.

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.

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.

Mammalian urinary bladder permeability is altered by cationic proteins: modulation by divalent cations

1994 ◽  
Vol 267 (4) ◽  
pp. C1013-C1026 ◽  
Author(s):  
C. J. Tzan ◽  
J. R. Berg ◽  
S. A. Lewis
Keyword(s):  
Urinary Bladder ◽  
Binding Site ◽  
Lipid Bilayers ◽  
Apical Membrane ◽  
Membrane Lipids ◽  
Divalent Cations ◽  
Membrane Conductance ◽  
Bladder Epithelium ◽  
Voltage Dependent ◽  
Phosphate Groups

It was previously demonstrated that protamine sulfate (PS, a cationic polypeptide) as well as synthetic cationic polypeptides (CpP, e.g., polylysine and polyarginine) caused an increase in the apical membrane conductance of the mammalian urinary bladder epithelium that was voltage dependent. The membrane conductance induced by these CpP was mediated by a saturable binding site and was partially blocked by CpP (self-inhibition). The PS-induced membrane conductance can be modified by polyvalent cations at three sites. The first site was to competitively inhibit the interaction of PS with an apical membrane binding site. The second site was to reversibly block the conductance induced by PS. The relative binding affinity (block of PS-induced conductance) sequence was as follows: UO2(2+) > La3+ > Mn2+ > Ba2+ > or = Ca2+ > Sr2+. Although La3+, Mn2+, Ba2+, Ca2+, and Sr2+ inhibited > or = 81% of the PS-induced conductance, UO2(2+) inhibited only 51% and Mg2+ was without effect. The third site was to increase the rate of loss of the PS-induced conductance from the apical membrane. Although neither carbodiimides (carboxyl group reactive reagents) nor neuraminidase (cleaves sialic acid residues) altered the effect of PS on the urinary bladder conductance, PS increased the conductance of lipid bilayers composed of negatively charged phospholipids. A candidate for the binding site might be the negatively charged phosphate groups of membrane lipids.

scholarly journals Effects of barium on the potassium conductance of squid axon.

1980 ◽  
Vol 75 (6) ◽  
pp. 727-750 ◽  
Author(s):  
D C Eaton ◽  
M S Brodwick
Keyword(s):  
Rate Constants ◽  
Dissociation Constants ◽  
Divalent Cations ◽  
Potassium Conductance ◽  
Competitive Inhibitor ◽  
Squid Axon ◽  
Voltage Dependent ◽  
Different Temperatures ◽  
Nanomolar Range ◽  
External K

Ba++ ion blocks K+ conductance at concentrations in the nanomolar range. This blockage is time and voltage dependent. From the time dependence it is possible to determine the forward and reverse rate constants for what appears to be an essentially first-order process of Ba++ interaction. The voltage dependence of the rate constants and the dissociation constants place the site of interaction near the middle of the membrane field. Comparison of the efficacy of Ba++ block at various internal K+ concentrations suggests that Ba++ is probably a simple competitive inhibitor of K+ interaction with the K+ conductance. The character of Ba++ block in high external K+ solutions suggests that Ba++ ion may be "knocked-off" the site by inward movement of external K+. Examination of the effects of other divalent cations suggests that the channel may have a closed state with a divalent cation inside the channel. The relative blockage at different temperatures implies a strong interaction between Ba++ and the K+ conductance.

On the electrical passivity of astrocyte potassium conductance

2021 ◽  
Author(s):  
Min Zhou ◽  
Yixing Du ◽  
Sydney Aten ◽  
David Terman
Keyword(s):  
Potassium Conductance ◽  
Membrane Conductance ◽  
Constant Field ◽  
Passive Behavior ◽  
Voltage Dependent ◽  
Junctional Coupling ◽  
Gap Junctional ◽  
Gap Junctional Coupling ◽  
Pore Domain ◽  
Inwardly Rectifying

Predominant expression of leak-type K+ channels provides astrocytes a high membrane permeability to K+ ions and a hyperpolarized membrane potential that are crucial for astrocyte function in brain homeostasis. In functionally mature astrocytes, the expression of leak K+ channels creates a unique membrane K+ conductance that lacks voltage-dependent rectification. Accordingly, the conductance is named ohmic or passive K+ conductance. Several inwardly rectifiers and two-pore domain K+ channels have been investigated for their contributions to passive conductance. Meanwhile, gap junctional coupling has been postulated to underlie the passive behavior of membrane conductance. It is now clear that the intrinsic properties of K+ channels and gap junctional coupling can each act alone or together to bring about a passive behavior of astrocyte conductance. Additionally, while the passive conductance can generally be viewed as a K+ conductance, the actual representation of this conductance is a combined expression of multiple known and unknown K+ channels, which has been further modified by the intricate morphology of individual astrocytes and syncytial gap junctional coupling. The expression of the inwardly rectifying K+ channels explains the inward-going component of passive conductance disobeying Goldman-Hodgkin-Kate (GHK) constant field outward rectification. However, the K+ channels encoding the outward-going passive currents remain to be determined in the future. Here, we review our current understanding of ion channels and biophysical mechanisms engaged in the passive astrocyte K+ conductance, propose new studies to resolve this long-standing puzzle in astrocyte physiology, and discuss the functional implication(s) of passive behavior of K+ conductance on astrocyte physiology.

Ionic mechanism of muscarinic cholinergic depolarization of mouse spinal cord neurons in cell culture

1983 ◽  
Vol 49 (3) ◽  
pp. 792-803 ◽  
Author(s):  
L. M. Nowak ◽  
R. L. Macdonald
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Channel Blocker ◽  
Potassium Conductance ◽  
Spinal Cord Neurons ◽  
M Current ◽  
Voltage Dependent ◽  
Muscarinic Cholinergic ◽  
Induced Currents ◽  
Reversal Potentials

1. Muscarinic cholinergic actions were investigated in a population of large multipolar spinal cord neurons in primary dissociated cell culture using conventional intracellular recording and single-microelectrode voltage-clamp techniques. 2. Cholinergic agonists were applied to the surface of neuronal somata by pressure ejecting drug-containing bathing medium from small blunt (2-10 microns) glass micropipettes. Atropine was applied by diffusion from large (20-30 microns) blunt micropipettes positioned near the soma. 3. Muscarine increased action-potential firing and evoked slow sustained membrane depolarization. Action potentials but not slow membrane depolarizations were eliminated by the sodium channel blocker, tetrodotoxin. Muscarine-induced depolarizing responses were unaffected by the calcium channel blocker, cadmium. 4. Depolarizing responses evoked by selective and nonselective muscarinic cholinergic agonists were dose dependent, reversibly antagonized by atropine, and did not desensitize. 5. Muscarine depolarized neurons and decreased membrane conductance during recording with both 3 M KCl- and 4 M KAc-filled intracellular recording micropipettes. When membrane potential was held constant using the single-electrode voltage-clamp technique (KCl-filled micropipettes), muscarine and gamma-aminobutyric acid (GABA) evoked inward currents at resting membrane potential. GABA-induced inward current responses were decreased by depolarization and had reversal potentials near -30 mV, consistent with GABA increasing chloride conductance. Muscarine-induced inward current responses were increased by depolarization and had extrapolated reversal potentials near -80 mV, consistent with muscarine decreasing a potassium conductance. 6. Unlike GABA-induced currents, muscarine-induced currents evoked in normal Tris-buffered saline (5 mM potassium) did not vary as a linear function of membrane potential and did not reverse polarity in six of seven neurons near potassium equilibrium potential. However, in high-potassium medium (15 mM) muscarinic responses did reverse polarity and current was linearly related to membrane potential. Thus, the apparent voltage dependence of muscarine responses was probably due to voltage dependency of the potassium conductance and not due to potassium channel rectification. 7. Preliminary evidence (37) indicates that muscarine decreases a time- and voltage-dependent potassium current in some cultured spinal cord neurons. Whether reduction of m current can completely account for muscarine postsynaptic actions in these cells remains unclear. Muscarine may also block a small population of non-voltage-dependent potassium channels in addition to reducing m current.

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