Serotonin and forskolin increase an inwardly rectifying potassium conductance in cultured identified Aplysia neurons

1987 ◽  
Vol 58 (5) ◽  
pp. 909-921 ◽  
Author(s):  
D. P. Lotshaw ◽  
I. B. Levitan
Keyword(s):  
Voltage Clamp ◽  
Potassium Conductance ◽  
Phosphodiesterase Inhibitor ◽  
Identified Neurons ◽  
Inward Rectification ◽  
Current Response ◽  
Aplysia Neurons ◽  
Voltage Dependent ◽  
K Concentration ◽  
Inwardly Rectifying

1. The effect of serotonin (5-HT) and forskolin on an inwardly rectifying K+ conductance (IKR) was studied using voltage-clamp techniques in several identified Aplysia neurons isolated and maintained in primary cell culture. 2. Inward rectification was observed in the current-voltage relationship of the identified neurons R15, R2, B1, and B2 and was predominately due to IKR, as demonstrated by the dependence of inward rectification on the extracellular K+ concentration, instantaneous kinetics of the membrane current response to hyperpolarizing voltage clamp pulses, and voltage-dependent Ba2+ block of the inwardly rectifying current. 3. 5-HT increased IKR conductance between 100 and 400% in the identified neuron R15 in culture and increased IKR conductance approximately 50% in the identified neurons B1, B2, and R2 in culture. The adenylate cyclase activator, forskolin, plus a phosphodiesterase inhibitor, Ro 20-1724, also increased IKR conductance in these neurons. 4. 5-HT and forskolin modulated other ion conductances as well in all of these cultured neurons.

Delay of desensitization onset by potassium ion in voltage-clamped frog muscle fibers

1985 ◽  
Vol 249 (5) ◽  
pp. C435-C446 ◽  
Author(s):  
A. A. Manthey
Keyword(s):  
Voltage Clamp ◽  
Acetylcholine Receptors ◽  
Transmembrane Potential ◽  
Direct Action ◽  
Direct Interaction ◽  
Frog Muscle ◽  
Average Potential ◽  
Voltage Dependent ◽  
Source Voltage ◽  
K Concentration

Increase in extracellular K+ concentration causes delay in desensitization onset during prolonged application of carbamylcholine to the postjunctional membrane in muscle. This could be due to a direct action of K+ on acetylcholine receptors or to some change in the receptors related to K+-induced effects on transmembrane potential. The question of direct vs. voltage-dependent action of K+ was investigated in frog muscle (Rana pipiens) using a point-source voltage clamp. In conductance measurements first without voltage control, desensitization rate in bath media containing 33 mM K+ was -0.198 s-1 among fibers showing an average potential of -30 mV and -0.104 s-1 in 165 mM K+ where the average potential was -2 mV, a decrease of 47%. By comparison, in voltage-clamp tests at a nominal holding potential of +20 mV, increasing extracellular K+ from 33 to 165 mM caused a decrease of 61% in desensitization rate from -0.151 to -0.059 s-1. Another series in 165 mM K+ at a holding level of +10 mV showed a decrease of 67% to a rate of 0.047 s-1. It is concluded that increases in extracellular K+ can delay desensitization onset independently of effects on transmembrane potential. It is suggested that this could result from a direct interaction of K+ with sites on the outer receptor moiety or within channels, but probably not at the inner membrane face, if the latter are considered in equilibrium with bulk intracellular K+.

Histamine depolarizes cholinergic septal neurons

1996 ◽  
Vol 75 (2) ◽  
pp. 707-714 ◽  
Author(s):  
N. Gorelova ◽  
P. B. Reiner
Keyword(s):  
Voltage Clamp ◽  
Receptor Agonist ◽  
Potassium Conductance ◽  
Input Resistance ◽  
Slow Inward Current ◽  
H1 Receptor ◽  
Inward Current ◽  
H2 Receptor ◽  
Inwardly Rectifying ◽  
Slow Depolarization

1. Bath application of 10 microM histamine (HA) resulted in a depolarization or inward current in 58/59 cholinergic neurons located in the medial septum and nucleus of the diagonal band of Broca (MS/DBB) in a slice preparation of rat brain. 2. In bridge mode, the histamine-induced depolarization consisted of both fast and slow phases; inward currents that followed the comparable time course were observed under voltage-clamp conditions. The fast depolarization was associated with variable changes in input resistance, while the slow depolarization always was associated with an increase in input resistance. 3. Both fast and slow responses persisted in the presence of tetrodotoxin (TTX), but only the fast response persisted when transmitter release was abolished by bathing the slice in either a low-Ca(2+)-, high-Mg(2+)-containing medium or one containing Cd2+. 4. When ramp voltage-clamp commands were applied during the fast depolarization, the resultant current-voltage (I-V) curves did not intersect over the range of membrane potentials from -130 to -30 mV. Ionic substitution experiments suggested that the bulk of the ionic current flowing during the fast depolarization was carried by sodium ions. 5. The I-V characteristics of the slow inward current identified it as a reduction in an inwardly rectifying potassium conductance. 6. The fast depolarization was significantly reduced by the H1 receptor antagonists pyrilamine and promethazine, but not by the H2 receptor antagonist cimetidine. Neither the H2 receptor agonist impromidine nor the H3 receptor agonist R-alpha-methylhistamine mimicked the response to HA. None of the agonists or antagonists had any observable effect upon the slow depolarization. 7. We conclude that HA directly depolarizes cholinergic MS/DBB neurons by acting as an H1 receptor, which primarily couples to an increase in a TTX-insensitive Na+ conductance. Additionally, HA evokes a slow depolarization mediated by a decrease in an inwardly rectifying potassium conductance but is not generated by activation of classically defined HA receptor subtypes.

C1 neurons of neonatal rats: intrinsic beating properties and alpha 2-adrenergic receptors

1995 ◽  
Vol 269 (6) ◽  
pp. R1356-R1369 ◽  
Author(s):  
Y. W. Li ◽  
D. A. Bayliss ◽  
P. G. Guyenet
Keyword(s):  
Adrenergic Receptors ◽  
Kynurenic Acid ◽  
Lucifer Yellow ◽  
Potassium Conductance ◽  
Ventrolateral Medulla ◽  
Inward Rectification ◽  
Hypotensive Drug ◽  
Outward Currents ◽  
Old Rats ◽  
Inwardly Rectifying

Tyrosine-hydroxylase-immunoreactive (TH-ir) neurons (C1 cells) of the rostral ventrolateral medulla (RVL) control sympathetic tone and may be inhibited by the hypotensive drug clonidine. The present study seeks to describe some of the intrinsic properties of bulbospinal C1 cells and to establish whether they have alpha 2-adrenergic inhibitory "autoreceptors." RVL bulbospinal cells (retrogradely labeled with microbeads) were recorded in thin slices from 3- to 7-day-old rats with patch electrodes containing Lucifer yellow. Forty-two of eighty-nine cells were recovered histologically, and 69% were TH-ir. The properties of TH-ir cells could not be distinguished from those of the other bulbospinal cells. Most cells were spontaneously active (0.5-5 spikes/s). Blockade of fast postsynaptic potentials with kynurenic acid plus bicuculline plus strychnine or with a low-Ca(2+)-high-Mg2+ medium failed to reduce their firing rate. The membrane trajectory consisted of one of two patterns interconvertible by injections of depolarizing or hyperpolarizing current: 1) depolarizing ramps leading to spikes or 2) slow oscillations (tetrodotoxin resistant but absent at hyperpolarized potentials) leading to spikes or repolarization. The cells had Ca(2+)-dependent afterhyperpolarizations, large transient outward currents, and a hyperpolarization-activated inward current activated at potentials less than -65 mV, blocked by CsCl, and presumably responsible for a large inward rectification. Of 27 TH-ir cells, 21 had inhibitory responses to alpha 2-adrenergic agonists. These were blocked by idazoxan (n = 9). alpha 2-Agonists activated an inwardly rectifying potassium conductance (KIR). We confirm that bulbospinal C1 cells have intrinsic pacemaker properties and demonstrate that they have alpha 2-adrenergic receptors (autoreceptors) coupled to KIR channels.

scholarly journals Voltage-dependent Inwardly Rectifying Potassium Conductance in the Outer Membrane of Neuronal Mitochondria

2010 ◽  
Vol 285 (35) ◽  
pp. 27411-27417 ◽  
Author(s):  
Francesca Fieni ◽  
Anjum Parkar ◽  
Thomas Misgeld ◽  
Martin Kerschensteiner ◽  
Jeff W. Lichtman ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Potassium Conductance ◽  
Voltage Dependent ◽  
Inwardly Rectifying

Arachidonic acid affects membrane ionic conductances of GH3 pituitary cells

1989 ◽  
Vol 257 (2) ◽  
pp. E203-E211 ◽  
Author(s):  
P. Vacher ◽  
J. McKenzie ◽  
B. Dufy
Keyword(s):  
Arachidonic Acid ◽  
Intracellular Calcium ◽  
Voltage Clamp ◽  
Calcium Concentration ◽  
Potassium Conductance ◽  
Free Calcium ◽  
Pituitary Cells ◽  
Prolactin Release ◽  
Ionic Conductances ◽  
Voltage Dependent

Arachidonic acid (AA) stimulates prolactin release from pituitary cells, by mechanisms not yet understood. In this work, we analyzed the effects of AA on membrane ionic conductances in a clonal line of anterior pituitary cells (GH3/B6), finding time- and dose-dependent effects of AA on their membrane ionic conductances. The predominant response at concentrations between 100 nM and 10 microM was a prolongation of the action potential (AP) and an increase in the transient after-hyperpolarization potential. Voltage clamp studies showed that this was associated with a decrease in a voltage-dependent potassium current and an increase in a voltage-dependent calcium current. In some cells (30%) the effect of AP duration was less important, but spike firing was enhanced. For the highest concentrations used (1 and 10 microM) the effects described above were preceded by hyperpolarization of the cell membrane; in voltage clamp it was shown that this hyperpolarization resulted from the activation of a calcium-dependent potassium conductance suspected to be due to the release of intracellular calcium. The calcium store affected by AA was, at least in part, insensitive to vanadate and heparin. These data suggest that AA may enhance intracellular calcium concentration by increasing calcium entry during each voltage-dependent calcium AP, by increasing the spike frequency, or by releasing calcium from an intracellular compartment. The resulting rise in cytosolic free calcium concentration may be a key link in the process by which AA stimulates prolactin release in GH3/B6 pituitary cells.

Serotonin and forskolin modulation of a chloride conductance in cultured identified Aplysia neurons

1987 ◽  
Vol 58 (5) ◽  
pp. 922-939 ◽  
Author(s):  
D. P. Lotshaw ◽  
I. B. Levitan
Keyword(s):  
Cell Culture ◽  
Voltage Clamp ◽  
Primary Cell Culture ◽  
Voltage Dependence ◽  
Reversal Potential ◽  
Aplysia Neurons ◽  
Voltage Dependent ◽  
Cl Conductance ◽  
Dependent Mechanism

1. The effect of serotonin (5-HT) and forskolin on a hyperpolarization activated Cl- conductance (gCl-) was studied using voltage-clamp techniques in identified Aplysia neurons maintained in primary cell culture. 2. The hyperpolarization-activated conductance induced by intracellular Cl- loading was carried by Cl- as determined by the following criteria: the extrapolated reversal potential of the current closely approximated the reversal potential of a cholinergic Cl- conductance, the current was not affected by extracellular ion substitutions other than Cl-, extracellular thiocyanate ions reversibly inhibited the current and the current exhibited slow voltage-dependent exponential kinetics similar to those described for the hyperpolarization-activated Cl- current in Aplysia neurons in situ. 3. In the identified neurons B1, B2, R15, and R2, 5-HT or forskolin reversibly inhibited gCl-, suggesting that 5-HT acted via an adenosine 3',5'-cyclic monophosphate-dependent mechanism. 4. Serotonergic inhibition resulted from a change in the voltage dependence of Cl- channel gating.

scholarly journals Electrostatics in the Cytoplasmic Pore Produce Intrinsic Inward Rectification in Kir2.1 Channels

2005 ◽  
Vol 126 (6) ◽  
pp. 551-562 ◽  
Author(s):  
Shih-Hao Yeh ◽  
Hsueh-Kai Chang ◽  
Ru-Chi Shieh
Keyword(s):  
Cell Types ◽  
Inward Rectifier ◽  
Inward Rectification ◽  
Membrane Excitability ◽  
Channel Inhibition ◽  
Charged Residues ◽  
Voltage Dependent ◽  
Inwardly Rectifying ◽  
Kir2.1 Channel ◽  
Positively Charged

Inward rectifier K+ channels are important in regulating membrane excitability in many cell types. The physiological functions of these channels are related to their unique inward rectification, which has been attributed to voltage-dependent block. Here, we show that inward rectification can also be induced by neutral and positively charged residues at site 224 in the internal vestibule of tetrameric Kir2.1 channels. The order of extent of inward rectification is E224K mutant > E224G mutant > wild type in the absence of internal blockers. Mutating the glycines at the equivalent sites to lysines also rendered weak inward rectifier Kir1.1 channels more inwardly rectifying. Also, conjugating positively charged methanethiosulfonate to the cysteines at site 224 induced strong inward rectification, whereas negatively charged methanethiosulfonate alleviated inward rectification in the E224C mutant. These results suggest that charges at site 224 may control inward rectification in the Kir2.1 channel. In a D172N mutant, spermine interacting with E224 and E299 induced channel inhibition during depolarization but did not occlude the pore, further suggesting that a mechanism other than channel block is involved in the inward rectification of the Kir2.1 channel. In this and our previous studies we showed that the M2 bundle crossing and selectivity filter were not involved in the inward rectification induced by spermine interacting with E224 and E299. We propose that neutral and positively charged residues at site 224 increase a local energy barrier, which reduces K+ efflux more than K+ influx, thereby producing inward rectification.

scholarly journals Mg2+-dependent Gating and Strong Inward Rectification of the Cation Channel TRPV6

2003 ◽  
Vol 121 (3) ◽  
pp. 245-260 ◽  
Author(s):  
Thomas Voets ◽  
Annelies Janssens ◽  
Jean Prenen ◽  
Guy Droogmans ◽  
Bernd Nilius
Keyword(s):  
Divalent Cations ◽  
Inward Rectification ◽  
Electrical Field ◽  
Gating Mechanism ◽  
Voltage Dependent ◽  
A Site ◽  
Inwardly Rectifying ◽  
Inside Out ◽  
Aspartate Residue

TRPV6 (CaT1/ECaC2), a highly Ca2+-selective member of the TRP superfamily of cation channels, becomes permeable to monovalent cations in the absence of extracellular divalent cations. The monovalent currents display characteristic voltage-dependent gating and almost absolute inward rectification. Here, we show that these two features are dependent on the voltage-dependent block/unblock of the channel by intracellular Mg2+. Mg2+ blocks the channel by binding to a site within the transmembrane electrical field where it interacts with permeant cations. The block is relieved at positive potentials, indicating that under these conditions Mg2+ is able to permeate the selectivity filter of the channel. Although sizeable outward monovalent currents were recorded in the absence of intracellular Mg2+, outward conductance is still ∼10 times lower than inward conductance under symmetric, divalent-free ionic conditions. This Mg2+-independent rectification was preserved in inside-out patches and not altered by high intracellular concentrations of spermine, indicating that TRPV6 displays intrinsic rectification. Neutralization of a single aspartate residue within the putative pore loop abolished the Mg2+ sensitivity of the channel, yielding voltage-independent, moderately inwardly rectifying monovalent currents in the presence of intracellular Mg2+. The effects of intracellular Mg2+ on TRPV6 are partially reminiscent of the gating mechanism of inwardly rectifying K+ channels and may represent a novel regulatory mechanism for TRPV6 function in vivo.

Inward rectification in mouse macrophages: evidence for a negative resistance region

1981 ◽  
Vol 241 (1) ◽  
pp. C9-C17 ◽  
Author(s):  
E. K. Gallin ◽  
D. R. Livengood
Keyword(s):  
Potassium Conductance ◽  
Barium Chloride ◽  
Negative Resistance ◽  
Peritoneal Macrophages ◽  
Inward Rectification ◽  
Transitional Region ◽  
Steady State Current ◽  
Mouse Macrophages ◽  
Voltage Dependent ◽  
Current Axis

The electrical properties of cultured mouse thioglycollate-induced peritoneal macrophages were investigated using intracellular recording techniques. Thirty-five percent of the cells studied had membrane potentials ranging from -65 to -95 mV and exhibited S-shaped, steady-state current-voltage (I-V) relationships containing a transitional region. Analysis of currents in the transitional region from the rate of rise and fall of the voltage responses to current pulses indicated the presence of a negative resistance region in this area. Tetrodotoxin (3 × 10(-5) M), cobalt chloride (3 mM), 4-aminopyridine (4 mM), and tetraethylammonium chloride (8 mM) did not eliminate the transitional region of the I-V curves, whereas addition of barium chloride (4 mM) and rubidium chloride (3 mM) did. Increasing the external concentration of potassium shifted the I-V relationship horizontally along the current axis but did not eliminate the transitional region. These data indicate that the inward rectification and the negative resistance region probably result from a voltage-dependent potassium 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.

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