scholarly journals A balance of outward and linear inward ionic currents is required for generation of slow-wave oscillations

2017 ◽  
Vol 118 (2) ◽  
pp. 1092-1104 ◽  
Author(s):  
Jorge Golowasch ◽  
Amitabha Bose ◽  
Yinzheng Guan ◽  
Dalia Salloum ◽  
Andrea Roeser ◽  
...  
Keyword(s):  
Slow Wave ◽  
Outward Current ◽  
Rhythmic Activity ◽  
Ionic Currents ◽  
Oscillatory Activity ◽  
Inward Current ◽  
Linear Current ◽  
Negative Conductance ◽  
Current Conductance ◽  
Slow Wave Oscillations

Pacemaker neuron-generated rhythmic activity requires the activation of at least one inward and one outward current. We have previously shown that the inward current can be a linear current (with negative conductance). Using this simple mechanism, here we demonstrate that the inward current conductance must be in relative balance with the outward current conductances to generate oscillatory activity. Surprisingly, an excess of outward conductances completely precludes the possibility of achieving such a balance.

Membrane currents recorded from a fragment of rabbit intestinal smooth muscle cell

1986 ◽  
Vol 251 (3) ◽  
pp. C335-C346 ◽  
Author(s):  
Y. Ohya ◽  
K. Terada ◽  
K. Kitamura ◽  
H. Kuriyama
Keyword(s):  
Smooth Muscle ◽  
Longitudinal Muscle ◽  
Outward Current ◽  
Ionic Currents ◽  
Muscle Layer ◽  
Dependent Manner ◽  
Rabbit Ileum ◽  
Longitudinal Muscle Layer ◽  
Inward Current ◽  
K Currents

Properties of ionic currents in smooth muscle membranes of the longitudinal muscle layer of the rabbit ileum were investigated using the single electrode voltage clamp method. In the present experiments, this method was applicable only to the smooth muscle ball (fragment) and not for the dispersed whole cell, because of incompleteness of the voltage clamping. A voltage step elicited a transient inward current followed by an outward current. This outward current was partly inhibited by Mn2+ or nisoldipine or by a reduction in the extracellular [Ca2+] ([Ca2+]o). Tetraethylammonium (TEA) reduced the delayed outward current in a dose-dependent manner, but 50 mM TEA did not produce a complete block of a residual current. When the pipette contained K+-free (Cs+ with TEA+) solution, the residual outward current was abolished. The inward current was elicited at -30 mV (holding potential of -60 mV) and reached the maximal value at +10 mV; the polarity was reversed at +60 mV. This inward current depended on the [Ca2+]o and was blocked by Mn2+ or nisoldipine. Ba2+ also permeated the membrane, and the inward current evoked by Ba2+ was also blocked by Mn2+ or nisoldipine. Reduction of [Na+]o in a solution containing 2.4 mM Ca2+ neither modified the current-voltage relation nor the decay of the inward current, but when [Ca2+]o was reduced to below 1 microM, Na+ permeated the membrane and was blocked by nisoldipine. In conclusion, ionic currents were recordable from the fragmented ball of the longitudinal muscle of rabbit ileum. There were at least two K+ currents as the outward current (Ca2+-dependent K+ and delayed K+ currents) and a Ca2+ current as the inward current. The property of the Ca2+ channel was similar to that observed with other preparations.

Ionic currents of cultured horizontal cells isolated from white perch retina

1986 ◽  
Vol 55 (3) ◽  
pp. 499-513 ◽  
Author(s):  
E. M. Lasater
Keyword(s):  
White Perch ◽  
Slow Component ◽  
Outward Current ◽  
Ionic Currents ◽  
Cell Types ◽  
Horizontal Cells ◽  
Inward Current ◽  
Whole Cell Patch Clamp ◽  
Anomalous Rectifier ◽  
K Concentration

Horizontal cells from the retinas of white perch were isolated and maintained in cell culture for 3 days to 3 wk. Four morphologically distinct types of horizontal cells could be identified in culture and were labeled types H1, H2, H3, and H4. Whole-cell patch-clamp techniques were used to study the ionic currents present in the four cell types. In all cells, depolarizing commands above threshold elicited a fast-inward current followed by an outward current. The fast-inward current was abolished by tetrodotoxin (TTX) or 0 Na+ Ringer's, indicating the current was carried by Na+. In H1, H2, and H3 cells, the outward current, carried by K+, consisted of two components: a transient current (IA), blockable with 4-aminopyridine (4-AP), tetraethylammonium (TEA), or intracellular cesium and a sustained current that could be blocked with TEA. The H4 cell had only the sustained current. An inward rectifying K+ current (anomalous rectifier) was observed in the four cell types. The current was sensitive to the extracellular K+ concentration. Its activation showed two components: an instantaneous component and a slower component. The slow component becomes faster with greater hyperpolarizations. The four cell types possessed a small, sustained Ca2+ current that, under normal conditions, was masked by the inward Na+ current and outward K+ currents.

The assembly of ionic currents in a thalamic neuron. II. The stability and state diagrams

1989 ◽  
Vol 237 (1288) ◽  
pp. 289-312 ◽  
Keyword(s):  
Outward Current ◽  
Ionic Currents ◽  
Stable Equilibrium Point ◽  
Thalamic Neuron ◽  
Thalamic Neurons ◽  
Inward Current ◽  
State Diagrams ◽  
Low Threshold ◽  
Current Steps ◽  
The Stability

In the previous model of a thalamic neuron (R. M. Rose & J. L. Hindmarsh, Proc. R. Soc. Lond . B 237, 267-288 (1989)), which we referred to as the z -model, the burst response was terminated by the slow activation of a subthreshold outward current. In this paper we show that similar results can be obtained if the burst response is terminated by slow inactivation of the subthreshold inward current, I s a . We illustrate the use of this new model, which we refer to as the h a -model, by using it to explain the response of a thalamic neuron to a double ramp current. The main aim of the paper is to show how the stability and state diagrams introduced previously can be used to explain various types of firing pattern of thalamic and other neurons. We show that increasing the threshold for the fast action potentials leads to low threshold spikes of increased amplitude. Also, addition of a second subthreshold inward current adds a new stability region, which enables us to explain the origin of plateau potentials. In addition, various types of subthreshold oscillation are produced by relocating a previously stable equilibrium point in an unstable region. Finally, we predict a sequence of responses to current steps from different levels of background current that extends the burst, rest, tonic sequence of thalamic neurons. The stability and state diagrams therefore provide us with a useful way of explaining further properties of thalamic neurons and appear to have further applications to other mammalian neurons.

scholarly journals The role of linear and voltage-dependent ionic currents in the generation of slow wave oscillations

2014 ◽  
Vol 37 (2) ◽  
pp. 229-242 ◽  
Author(s):  
Amitabha Bose ◽  
Jorge Golowasch ◽  
Yinzheng Guan ◽  
Farzan Nadim
Keyword(s):  
Slow Wave ◽  
Ionic Currents ◽  
Voltage Dependent ◽  
Slow Wave Oscillations

scholarly journals A balance of outward and linear inward ionic currents is required for the generation of slow wave oscillations

2017 ◽  
Author(s):  
Jorge Golowasch ◽  
Amitabha Bose ◽  
Yinzheng Guan ◽  
Dalia Salloum ◽  
Andrea Roeser ◽  
...  
Keyword(s):  
Outward Current ◽  
Ionic Currents ◽  
Oscillatory Activity ◽  
Negative Slope ◽  
High Threshold ◽  
Dynamic Clamp ◽  
Cancer Borealis ◽  
Slow Oscillations ◽  
Pyloric Network ◽  
Inward Currents

AbstractRegenerative inward currents help produce slow oscillations through a negative-slope conductance region of their current-voltage relationship that is well approximated by a linear negative conductance. We used dynamic clamp injections of a linear current with this conductance, INL, to explore why some neurons can generate intrinsic slow oscillations whereas others cannot. We addressed this question, in synaptically isolated neurons of the crab Cancer borealis, after blocking action potentials. The pyloric network consists of distinct pacemaker group and follower neurons, all of which express the same complement of ionic currents. When the pyloric dilator (PD) neuron, a member of the pacemaker group, was injected with INL using dynamic clamp, it consistently produced slow oscillations. In contrast, the lateral pyloric (LP) or ventral pyloric (VD) follower neurons, failed to oscillate with INL. To understand these distinct behaviors, we compared outward current levels of PD, LP and VD neurons. We found that LP and VD neurons had significantly larger high-threshold potassium currents (IHTK) than PD, and LP had lower transient potassium current, IA. Reducing IHTK pharmacologically enabled both LP and VD neurons to produce oscillations with INL, whereas modifying IA levels did not affect INL-induced oscillations. Using phase-plane and bifurcation analysis of a simplified model cell, we demonstrate that large levels of IHTK can block INL-induced oscillatory activity, whereas generation of oscillations is almost independent of IA levels. These results demonstrate the importance of a balance between inward pacemaking currents and high-threshold K+current levels in determining slow oscillatory activity.

Ionic currents in identified swimmeret motor neurones of the crayfish Pacifastacus leniusculus

1995 ◽  
Vol 198 (7) ◽  
pp. 1483-1492 ◽  
Author(s):  
A Chrachri
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Rhythmic Activity ◽  
Ionic Currents ◽  
Power Stroke ◽  
Transient Outward Current ◽  
Patch Clamp Technique ◽  
Outward Currents ◽  
Inward Currents ◽  
Motor Neurones

Ionic currents from freshly isolated and identified swimmeret motor neurones were characterized using a whole-cell patch-clamp technique. Two outward currents could be distinguished. A transient outward current was elicited by delivering depolarizing voltage steps from a holding potential of -80 mV. This current was inactivated by holding the cells at a potential of -40 mV and was also blocked completely by 4-aminopyridine. A second current had a sustained time course and continued to be activated at a holding potential of -40 mV. This current was partially blocked by tetraethylammonium. These outward currents resembled two previously described potassium currents: the K+ A-current and the delayed K+ rectifier current respectively. Two inward currents were also detected. A fast transient current was blocked by tetrodotoxin and inactivated at holding potential of -40 mV, suggesting that this is an inward Na+ current. A second inward current had a sustained time course and was affected neither by tetrodotoxin nor by holding the cell at a potential of -40 mV. This current was substantially enhanced by the addition of Ba2+ to the bath or when equimolar Ba2+ replaced Ca2+ as the charge carrier. Furthermore, this current was significantly suppressed by nifedipine. All these points suggest that this is an L-type Ca2+ current. Bath application of nifedipine into an isolated swimmeret preparation affected both the frequency of the swimmeret rhythm and the duration of power-stroke activity, suggesting an important role for the inward Ca2+ current in maintaining a regular swimmeret rhythmic activity in crayfish.

scholarly journals Ionic Mechanism Underlying Recovery of Rhythmic Activity in Adult Isolated Neurons

2006 ◽  
Vol 96 (4) ◽  
pp. 1860-1876 ◽  
Author(s):  
Rodolfo J. Haedo ◽  
Jorge Golowasch
Keyword(s):  
Activity Patterns ◽  
Stimulus Frequency ◽  
Rhythmic Activity ◽  
Ionic Currents ◽  
Network Activity ◽  
Nonlinear Dependence ◽  
Oscillatory Activity ◽  
High Threshold ◽  
Ionic Mechanisms ◽  
Regulation Of Activity

Neurons exhibit long-term excitability changes necessary for maintaining proper cell and network activity in response to various inputs and perturbations. For instance, the adult crustacean pyloric network can spontaneously recover rhythmic activity after complete shutdown resulting from permanent removal of neuromodulatory inputs. Dissociated lobster stomatogastric ganglion (STG) neurons have been shown to spontaneously develop oscillatory activity via excitability changes. Rhythmic electrical stimulation can eliminate these oscillatory patterns in some cells. The ionic mechanisms underlying these changes are only partially understood. We used dissociated crab STG neurons to study the ionic mechanisms underlying spontaneous recovery of rhythmic activity and stimulation-induced activity changes. Similar to lobster neurons, rhythmic activity spontaneously develops in crab STG neurons. Rhythmic hyperpolarizing stimulation can eliminate, but more commonly accelerate, the emergence of stable oscillatory activity depending on Ca2+ influx at hyperpolarized voltages. Our main finding is that upregulation of a Ca2+ current and downregulation of a high-threshold K+ current underlies the spontaneous homeostatic development of oscillatory activity. However, because of a nonlinear dependence on stimulus frequency, hyperpolarization-induced oscillations appear to be inconsistent with a homeostatic regulation of activity. We find no difference in the activity patterns or the underlying ionic currents involved between neurons of the fast pyloric and the slow gastric mill networks during the first 10 days in isolation. Dynamic-clamp experiments confirm that these conductance modifications can explain the observed activity changes. We conclude that spontaneous and stimulation-induced excitability changes in STG neurons can both result in intrinsic oscillatory activity via regulation of the same two conductances.

Current-Voltage Relations in the Isolated Giant Axon of the Cockroach Under Voltage-Clamp Conditions

1967 ◽  
Vol 47 (2) ◽  
pp. 343-355
Author(s):  
Y. PICHON ◽  
J. BOISTEL
Keyword(s):  
Action Potentials ◽  
Outward Current ◽  
Node Of Ranvier ◽  
Ionic Currents ◽  
Giant Axon ◽  
Inward Current ◽  
Outward Currents ◽  
Current Voltage ◽  
Inward Currents ◽  
Na Ions

1. An experimental method of recording and controlling the membrane potential of a small area of the membrane of the cockroach giant axon is described. 2. The recorded action potentials were essentially similar to those previously recorded by other methods. 3. The membrane currents resemble those reported for the squid axon, the node of Ranvier in frog nerve and the lobster giant axon. 4. Small cathodal polarizations gave only small outward currents; larger depolarizations (10-100 mV.) gave an initial inward current which changed into a delayed outward current. 5. The initial inward current attained a maximum with depolarizing pulses of 40-50 mV. and showed a reversed, outward, flow of about 100 mV. 6. Delayed outward currents increased continuously with increasing impulse voltage. 7. The initial inward current was larger when the pulse was preceded by an hyperpolarizing prepulse. 8. It is concluded that, although the early inward currents were in all probability related to Na+ ions and the delayed outward currents to K+ ions, the possible participation of Ca2+ and Cl- ions to the ionic currents cannot be excluded.

P2X(4) purinoceptors mediate an ATP-activated, non-selective cation current in rabbit osteoclasts

1999 ◽  
Vol 112 (23) ◽  
pp. 4425-4435 ◽  
Author(s):  
L.N. Naemsch ◽  
A.F. Weidema ◽  
S.M. Sims ◽  
T.M. Underhill ◽  
S.J. Dixon
Keyword(s):  
Outward Current ◽  
Osteoclast Formation ◽  
Extracellular Nucleotides ◽  
Patch Clamp Recording ◽  
Inward Current ◽  
Reverse Transcription Pcr ◽  
Cation Current ◽  
Degenerate Oligonucleotide ◽  
Base Pair Fragment ◽  
Pair Fragment

Extracellular nucleotides act as signaling molecules in numerous tissues. In bone, nucleotides stimulate osteoclast formation and activity; however, the receptors and signaling mechanisms underlying these effects have yet to be identified. To identify specific P2X purinoceptor subtypes in osteoclasts, degenerate oligonucleotide primers were used to PCR-amplify DNA fragments from a rabbit osteoclast cDNA library. A 372-base-pair fragment was obtained that encoded an amino acid sequence with 88% identity to the rat P2X(4) purinoceptor. The presence of P2X(4) mRNA in purified osteoclasts was confirmed by reverse transcription-PCR. Endogenous purinoceptors were functionally characterized in isolated rabbit osteoclasts by patch-clamp recording in whole-cell configuration. At negative membrane potentials, application of ATP or ADP rapidly activated an inward current followed by an outward current. In contrast, UTP or ADPbetaS elicited only an outward current, due to activation of a Ca(2+)-dependent K(+) conductance. The initial inward current was non-selective for cations and inactivated during agonist application. Furthermore, the inward current was insensitive to suramin and Cibacron blue, and was potentiated by Zn(2+). These characteristics are consistent with properties of P2X(4) purinoceptors. Activation of P2X(4) purinoceptors leads to cation influx and depolarization. Nucleotides, released at sites of trauma or inflammation, may act through these receptors on osteoclasts to stimulate bone resorption.

Whole cell current analyses of pancreatic acinar AR42J cells. I. Voltage- and Ca(2+)-activated currents

1991 ◽  
Vol 260 (5) ◽  
pp. C934-C948 ◽  
Author(s):  
K. Kusano ◽  
H. Gainer
Keyword(s):  
Reversal Potential ◽  
Outward Current ◽  
Pancreatic Acinar Cells ◽  
Equilibrium Potential ◽  
Channel Blockers ◽  
Whole Cell ◽  
Inward Current ◽  
Tail Current ◽  
Ar42j Cells ◽  
Conductance Increase

Voltage- and Ca(2+)-activated whole cell currents were studied in AR42J cells, a clonal cell line derived from rat pancreatic acinar cells, using a patch electrode voltage-clamp technique. Four kinds of ionic currents were identified by their ionic dependencies, pharmacological properties, and kinetic parameters: 1) an outward current flow due mainly to a voltage-dependent K(+)-conductance increase, 2) an initial transient inward current due to an Na(+)-conductance increase, 3) transient and long-duration inward current due to a Ca(2+)-conductance increase, and 4) a slowly activating inward current that persists over the duration of the depolarizing pulse and deactivates slowly upon repolarization, producing a slow inward tail current. The slow inward tail current was particularly robust and was interpreted as due to a Ca(2+)-activated Cl(-)-conductance increase, since 1) the generation of this current was blocked by removing the extracellular Ca2+, applying Ca(2+)-channel blockers (Cd2+, nifedipine), or by lowering the intracellular Ca2+ concentration [( Ca2+]i) with EGTA; and 2) the reversal potential (Erev) of the slow inward tail current was close to 0 mV in the control condition (152 mM [Cl-]o/154 mM [Cl-]i), and changes of the [Cl-]o/[Cl )i ratio shifted the Erev toward the predicted Cl- equilibrium potential.

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