Voltage-gated currents of rabbit A- and B-type horizontal cells in retinal monolayer cultures

1994 ◽  
Vol 11 (2) ◽  
pp. 369-378 ◽  
Author(s):  
Stefan Löhrke ◽  
Hans-Dieter Hofmann
Keyword(s):  
Single Channel ◽  
Ionic Currents ◽  
Calcium Currents ◽  
Horizontal Cells ◽  
Delayed Rectifier ◽  
Patch Clamp Recording ◽  
Voltage Gated ◽  
Monolayer Cultures ◽  
Inward Currents

AbstractIn monolayer cultures prepared from immature early postnatal rabbit retina, small populations of neurons can be demonstrated to differentiate into apparently mature A- and B-type horizontal cells. Using wholecell, single-channel, patch-clamp recording techniques, we have analyzed the pattern of voltage-gated conductances expressed by mammalian horizontal cells under these conditions. A total of six different voltage-dependent ionic currents were recorded. Tetrodotoxin-sensitive fast sodium inward currents (INa) were found in 81% of the A-type and 90% of the B-type cells. Inward calcium currents could be demonstrated in all cells tested after blockade of other conductances. Two types of outward potassium currents with properties of the 4–aminopyridine-sensitive transient IA and the tetraethylammonium sensitive delayed rectifier IK, respectively, could be characterized in whole-cell recordings. An inward rectifying potassium current (Ianom) typical for horizontal cells was activated in response to hyperpolarizing voltage steps. These types of currents have also been described in dissociated adult horizontal cells from lower vertebrates and cat. With single-channel recordings on inside-out patches excised from B-type cells, an additional Ca2+-dependent current (IK(Ca)) was observed which, so far, has not been described in horizontal cells developing in situ. Our results demonstrate that cultured rabbit horizontal cells express a set of voltage-gated currents which largely, but not completely, corresponds to that described in situ for horizontal cells of other species. The culture system will allow further investigation of developmental and functional aspects of mammalian horizontal cells.

Dopamine Modulation of Calcium Currents in Pyloric Neurons of the Lobster Stomatogastric Ganglion

2003 ◽  
Vol 90 (2) ◽  
pp. 631-643 ◽  
Author(s):  
Bruce R. Johnson ◽  
Peter Kloppenburg ◽  
Ronald M. Harris-Warrick
Keyword(s):  
Calcium Channel ◽  
Transmitter Release ◽  
Stomatogastric Ganglion ◽  
Calcium Currents ◽  
Voltage Gated ◽  
Pyloric Network ◽  
Pyloric Dilator ◽  
Voltage Dependent ◽  
Inward Currents ◽  
Dopamine Modulation

We examined the dopamine (DA) modulation of calcium currents (ICa) that could contribute to the plasticity of the pyloric network in the lobster stomatogastric ganglion. Pyloric somata were voltage-clamped under conditions designed to block voltage-gated Na+, K+, and H currents. Depolarizing steps from –60 mV generated voltage-dependent, inward currents that appeared to originate in electrotonically distal, imperfectly clamped regions of the cell. These currents were blocked by Cd2+ and enhanced by Ba2+ but unaffected by Ni2+. Dopamine enhanced the peak ICa in the pyloric constrictor (PY), lateral pyloric (LP), and inferior cardiac (IC) neurons and reduced peak ICa in the ventricular dilator (VD), pyloric dilator (PD), and anterior burster (AB) neurons. All of these effects, except for the AB, are consistent with DA's excitation or inhibition of firing in the pyloric neurons. Enhancement of ICa in PY and LP neurons and reduction of ICa in VD and PD neurons are also consistent with DA-induced synaptic strength changes via modulation of presynaptic ICa. However, the reduction of ICa in AB suggests that DA's enhancement of AB transmitter release is not directly mediated through presynaptic ICa. ICa in PY and PD neurons was more sensitive to nifedipine block than in AB neurons. In addition, nifedipine blocked DA's effects on ICa in the PY and PD neurons but not in the AB neuron. Thus the contribution of specific calcium channel subtypes carrying the total ICa may vary between pyloric neuron classes, and DA may act on different calcium channel subtypes in the different pyloric neurons.

Effect of Prozac on whole cell ionic currents in lens and corneal epithelia

1995 ◽  
Vol 269 (1) ◽  
pp. C250-C256 ◽  
Author(s):  
J. L. Rae ◽  
A. Rich ◽  
A. C. Zamudio ◽  
O. A. Candia
Keyword(s):  
Potassium Channels ◽  
Single Channel ◽  
Ionic Currents ◽  
Current Amplitude ◽  
Human Lens ◽  
Delayed Rectifier ◽  
Open Probability ◽  
Channel Current ◽  
Single Channel Current ◽  
Ionic Conductances

Prozac (fluoxetine), a compound used therapeutically in humans to combat depression, has substantial effects on ionic conductances in rabbit corneal epithelial cells and in cultured human lens epithelium. In corneal epithelium, it reduces the current due to the large-conductance potassium channels that dominate this preparation. Its effects seem largely to decrease the open probability while leaving the single-channel current amplitude unaltered. In cultured human epithelium, currents from calcium-activated potassium channels and inward rectifiers are unaffected by Prozac. Delayed-rectifier potassium currents are reduced by Prozac in a complicated way that involves both gating and single-channel current amplitude. Fast tetrodotoxin-blockable sodium currents are also decreased by Prozac in this preparation. For all of these ion conductance effects, Prozac concentrations of 10(-5) to 10(-4) M are required. Whereas these levels are 10- to 100-fold higher than the plasma levels achieved in therapeutic use in humans, they are comparable to or less than levels needed for many other blockers of the ionic conductances studied here.

scholarly journals Effect of FMRFamide on voltage-dependent currents in identified centrifugal neurons of the optic lobe of the cuttlefish, Sepia officinalis

2020 ◽  
Author(s):  
Abdesslam Chrachri
Keyword(s):  
Visual Processing ◽  
Calcium Current ◽  
Optic Lobe ◽  
Low Voltage ◽  
Sodium Current ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents

AbstractWhole-cell patch-clamp recordings from identified centrifugal neurons of the optic lobe in a slice preparation allowed the characterization of five voltage-dependent currents; two outward and three inward currents. The outward currents were; the 4-aminopyridine-sensitive transient potassium or A-current (IA), the TEA-sensitive sustained current or delayed rectifier (IK). The inward currents were; the tetrodotoxin-sensitive transient current or sodium current (INa). The second is the cobalt- and cadmium-sensitive sustained current which is enhanced by barium and blocked by the dihydropyridine antagonist, nifedipine suggesting that it could be the L-type calcium current (ICaL). Finally, another transient inward current, also carried by calcium, but unlike the L-type, this current is activated at more negative potentials and resembles the low-voltage-activated or T-type calcium current (ICaT) of other preparations.Application of the neuropeptide FMRFamide caused a significant attenuation to the peak amplitude of both sodium and sustained calcium currents without any apparent effect on the transient calcium current. Furthermore, FMRFamide also caused a reduction of both outward currents in these centrifugal neurons. The fact that FMRFamide reduced the magnitude of four of five characterized currents could suggest that this neuropeptide may act as a strong inhibitory agent on these neurons.SummaryFMRFamide modulate the ionic currents in identified centrifugal neurons in the optic lobe of cuttlefish: thus, FMRFamide could play a key role in visual processing of these animals.

scholarly journals Complex electrophysiological remodeling in postinfarction ischemic heart failure

2018 ◽  
Vol 115 (13) ◽  
pp. E3036-E3044 ◽  
Author(s):  
Bence Hegyi ◽  
Julie Bossuyt ◽  
Leigh G. Griffiths ◽  
Rafael Shimkunas ◽  
Zana Coulibaly ◽  
...  
Keyword(s):  
Heart Failure ◽  
Single Channel ◽  
Ionic Currents ◽  
Border Zone ◽  
Delayed Rectifier ◽  
Large Animal ◽  
Current Profile ◽  
Large Animal Models ◽  
Remote Zone ◽  
Arrhythmogenic Substrate

Heart failure (HF) following myocardial infarction (MI) is associated with high incidence of cardiac arrhythmias. Development of therapeutic strategy requires detailed understanding of electrophysiological remodeling. However, changes of ionic currents in ischemic HF remain incompletely understood, especially in translational large-animal models. Here, we systematically measure the major ionic currents in ventricular myocytes from the infarct border and remote zones in a porcine model of post-MI HF. We recorded eight ionic currents during the cell’s action potential (AP) under physiologically relevant conditions using selfAP-clamp sequential dissection. Compared with healthy controls, HF-remote zone myocytes exhibited increased late Na+ current, Ca2+-activated K+ current, Ca2+-activated Cl− current, decreased rapid delayed rectifier K+ current, and altered Na+/Ca2+ exchange current profile. In HF-border zone myocytes, the above changes also occurred but with additional decrease of L-type Ca2+ current, decrease of inward rectifier K+ current, and Ca2+ release-dependent delayed after-depolarizations. Our data reveal that the changes in any individual current are relatively small, but the integrated impacts shift the balance between the inward and outward currents to shorten AP in the border zone but prolong AP in the remote zone. This differential remodeling in post-MI HF increases the inhomogeneity of AP repolarization, which may enhance the arrhythmogenic substrate. Our comprehensive findings provide a mechanistic framework for understanding why single-channel blockers may fail to suppress arrhythmias, and highlight the need to consider the rich tableau and integration of many ionic currents in designing therapeutic strategies for treating arrhythmias in HF.

The Neuromuscular Junction Revisited: Ca2+ Channels and Transmitter Release in Cholinergic Neurones in Xenopus Nerve and Muscle Cell Culture

1990 ◽  
Vol 153 (1) ◽  
pp. 129-140 ◽  
Author(s):  
T. P. FENG ◽  
ZHENG-SHAN DAI
Keyword(s):  
Neuromuscular Junction ◽  
Transmitter Release ◽  
Single Channel ◽  
Calcium Currents ◽  
Patch Clamps ◽  
Whole Cell ◽  
Voltage Gated ◽  
Cholinergic Neurones ◽  
Ca2 Channels ◽  
Evoked Transmitter Release

Although the entry of calcium ions into the presynaptic nerve terminals through voltage-gated Ca2+ channels is now universally recognized as playing an essential role in evoked transmitter release at the neuromuscular junction (NMJ), and indeed in chemical synapses generally, we have as yet very little direct knowledge of the Ca2+ channels of the presynaptic terminals. In this work, making use of cocultured nerve and muscle cells from Xenopus embryos, we studied the NMJ formed between the soma of identified cholinergic neurones and myoball, which allowed the use of patch-clamps on both the pre- and postsynaptic components. Both whole-cell and single-channel recordings of Ca2+ channels in the presynaptic cell were made. We found only one type of voltage-gated Ca2+ channel with highvoltage activation and slow inactivation characteristics, allowing its classification either as the L or the N type. The channels were susceptible to block by metenkephalin but not to block by nifedipine or to enhancement by Bay K 8644. This combination of pharmacological properties favours their classification as the N type. Preliminary observations on the correlation between calcium currents and transmitter release disclosed a strikingly rapid run-down of the evoked release with unchanged calcium currents and spontaneous release during whole-cell recording, indicating a specific wash-out effect on some link between calcium entry and evoked transmitter release.

Patch-clamp recording in myenteric neurons of guinea pig small intestine

1992 ◽  
Vol 262 (6) ◽  
pp. G1074-G1078 ◽  
Author(s):  
L. V. Baidan ◽  
A. V. Zholos ◽  
M. F. Shuba ◽  
J. D. Wood
Keyword(s):  
Small Intestine ◽  
Patch Clamp ◽  
Guinea Pig ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Recording ◽  
Myenteric Neurons ◽  
Delayed Rectifier Current ◽  
Outward Currents ◽  
Current Clamp Mode

The results of our research established the feasibility of applying patch-clamp methods in the study of the cellular neurophysiology of myenteric neurons enzymatically dissociated from adult guinea pig small intestine. Recording in current-clamp mode revealed two populations of neurons. One population discharged repetitively during depolarizing current pulses and displayed anodal-break excitation reminiscent of S/type 1 myenteric neurons. In the second population, spike discharge was limited to one or two spikes at the onset of depolarizing pulses and was similar to the behavior of AH/type 2 neurons. Recording in voltage-clamp mode revealed a complex of overlapping inward and outward whole cell currents. Fast and slow components of inward current were interpreted as sodium and calcium currents, respectively. Outward currents were blocked by cesium and consisted of components with properties of delayed rectifier current and A-type potassium current.

Modulatory effects of 5-hydroxytryptamine on voltage-activated currents in cultured antennal lobe neurones of the sphinx moth Manduca sexta.

1995 ◽  
Vol 198 (3) ◽  
pp. 613-627 ◽  
Author(s):  
A R Mercer ◽  
J H Hayashi ◽  
J G Hildebrand
Keyword(s):  
Manduca Sexta ◽  
Adult Development ◽  
Antennal Lobe ◽  
Ionic Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Recording ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
Reversible Reduction

The modulatory effects of 5-hydroxytryptamine (5-HT or serotonin) on voltage-gated currents in central olfactory neurones of the moth Manduca sexta have been examined in vitro using whole-cell patch-clamp recording techniques. Central olfactory neurones were dissociated from the antennal lobes of animals at stage 5 of the 18 stages of metamorphic adult development. The modulatory actions of 5-HT on voltage-activated ionic currents were examined in a subset of morphologically identifiable antennal lobe neurones maintained for 2 weeks in primary cell culture. 5-HT caused reversible reduction of both a rapidly activating A-type K+ current and a relatively slowly activating K+ current resembling a delayed rectifier-type conductance. 5-HT also reduced the magnitude of voltage-activated Ca2+ influx in these cells. The functional significance of 5-HT-modulation of central neurones is discussed.

scholarly journals Synergistic Inhibition of Delayed Rectifier K+ and Voltage-Gated Na+ Currents by Artemisinin in Pituitary Tumor (GH3) Cells

2017 ◽  
Vol 41 (5) ◽  
pp. 2053-2066 ◽  
Author(s):  
Edmund Cheung So ◽  
Sheng-Nan Wu ◽  
Ping-Ching Wu ◽  
Hui-Zhen  Chen ◽  
Chia-Jung Yang
Keyword(s):  
Pituitary Tumor ◽  
Ionic Currents ◽  
Neuroendocrine Cells ◽  
Endocrine Function ◽  
Gh3 Cells ◽  
Delayed Rectifier ◽  
Membrane Excitability ◽  
Inactivation Curve ◽  
Voltage Gated

Background: Artemisinin (ART) is an anti-malarial agent reported to influence endocrine function. Methods: Effects of ART on ionic currents and action potentials (APs) in pituitary tumor (GH3) cells were evaluated by patch clamp techniques. Results: ART inhibited the amplitude of delayed-rectifier K+ current (IK(DR)) in response to membrane depolarization and accelerated the process of current inactivation. It exerted an inhibitory effect on IK(DR) with an IC50 value of 11.2 µM and enhanced IK(DR) inactivation with a KD value of 14.7 µM. The steady-state inactivation curve of IK(DR) was shifted to hyperpolarization by 10 mV. Pretreatment of chlorotoxin (1 µM) or iloprost (100 nM) did not alter the magnitude of ART-induced inhibition of IK(DR) in GH3 cells. ART also decreased the peak amplitude of voltage-gated Na+ current (INa) with a concentration-dependent slowing in inactivation rate. Application of KMUP-1, an inhibitor of late INa, was effective at reversing ART-induced prolongation in inactivation time constant of INa. Under current-clamp recordings, ART alone reduced the amplitude of APs and prolonged the duration of APs. Conclusion: Under ART exposure, the inhibitory actions on both IK(DR) and INa could be a potential mechanisms through which this drug influences membrane excitability of endocrine or neuroendocrine cells appearing in vivo.

Sustained and transient potassium currents of cultured horizontal cells isolated from white bass retina

1990 ◽  
Vol 64 (6) ◽  
pp. 1758-1766 ◽  
Author(s):  
J. M. Sullivan ◽  
E. M. Lasater
Keyword(s):  
Potassium Current ◽  
Potassium Currents ◽  
Calcium Currents ◽  
Horizontal Cells ◽  
Delayed Rectifier ◽  
White Bass ◽  
A Value ◽  
Outward Potassium Current ◽  
A Current

1. Horizontal cells (HCs) are second-order neurons in the retina that receive direct photoreceptor input. They rest at around -20 mV in the dark, because of the continuous release of neurotransmitter from photoreceptors. HCs respond to light with graded hyperpolarizations, which can reach -70 to -80 mV in the presence of very bright stimuli. 2. HCs from the retinas of white bass were isolated and maintained in culture. Potassium currents in three morphological types of HCs--H1, H2, and H4--were studied in culture with whole-cell, patch-clamp techniques, when sodium and calcium currents were blocked. 3. A transient outward potassium current (IA), with many characteristics of the A-current, was found in all H2s and H4s but only occasionally in H1s. The threshold for activation of this current was around -40 mV, a value more depolarized than usual for the A-current. The peak IA was typically smaller than 300 pA when the membrane was stepped from a holding potential of -70 mV to a command potential of -10 mV, the upper limit of the in vivo range of HC membrane potentials. Steady-state inactivation is expected to reduce the magnitude of IA in vivo. 4. A sustained outward potassium current (IK) was found in all types of HCs. This sustained potassium current did not activate until the membrane was stepped to potentials above -10 mV, a value much more depolarized than those reported for the delayed rectifier current in other neurons. As a result, IK is absent over the in vivo operating range of these cells. 5. No calcium-dependent potassium current was found in any cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Voltage-dependent ionic currents in solitary horizontal cells isolated from cat retina

1992 ◽  
Vol 68 (4) ◽  
pp. 1143-1150 ◽  
Author(s):  
Y. Ueda ◽  
A. Kaneko ◽  
M. Kaneda
Keyword(s):  
Potassium Current ◽  
Horizontal Cell ◽  
Potassium Currents ◽  
Ionic Currents ◽  
Horizontal Cells ◽  
Membrane Properties ◽  
Resting Potential ◽  
Delayed Rectifier ◽  
Cat Retina ◽  
Voltage Dependent

1. Horizontal cells of the cat retina were isolated by enzymatic dissociation. Two types of horizontal cells were identified: the axonless (A-type) horizontal cell having four to six thick, long (approximately 100 microns) dendrites, and the short-axon (B-type) horizontal cell having many (> 5) fine, short (approximately 30 microns) dendrites. 2. Membrane properties of isolated horizontal cells were analyzed under current-clamp and voltage-clamp conditions. In the A-type cell, the average resting potential was -55 mV and the mean membrane capacitance was 110 pF, whereas values in the B-type cell were -58 mV and 40 pF, respectively. The A-type cell showed long-lasting Ca spikes, but B-type cells had no Ca spikes. 3. Five types of voltage-dependent ionic currents were recorded: a sodium current (INa), a calcium current (ICa), and three types of potassium currents. Potassium currents consisted of potassium current through the inward rectifier (Ianomal), transient outward potassium current (IA), and potassium current through the delayed rectifier (IK(v)). INa was recorded only from A-type cells. Other currents were recorded from both types of cells. 4. INa activated when cells were depolarized from a holding potential (Vh) of -95 mV, and it was maximal at -25 mV. This current was blocked by tetrodotoxin. Approximately half of the A-type cells had INa, but no B-type cell had this current. 5. L-type ICa, an inward-going sustained current, was activated with depolarization more positive than -25 mV. Current amplitude reached a maximal value near 15 mV and became smaller with further depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

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