scholarly journals HCN channel-mediated neuromodulation can control action potential velocity and fidelity in central axons

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Niklas Byczkowicz ◽  
Abdelmoneim Eshra ◽  
Jacqueline Montanaro ◽  
Andrea Trevisiol ◽  
Johannes Hirrlinger ◽  
...  
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Mossy Fiber ◽  
Mossy Fibers ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Resting Membrane Potential ◽  
Immunogold Electron Microscopy ◽  
Hcn Channels ◽  
Hcn Channel

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels control electrical rhythmicity and excitability in the heart and brain, but the function of HCN channels at the subcellular level in axons remains poorly understood. Here, we show that the action potential conduction velocity in both myelinated and unmyelinated central axons can be bidirectionally modulated by a HCN channel blocker, cyclic adenosine monophosphate (cAMP), and neuromodulators. Recordings from mouse cerebellar mossy fiber boutons show that HCN channels ensure reliable high-frequency firing and are strongly modulated by cAMP (EC50 40 µM; estimated endogenous cAMP concentration 13 µM). In addition, immunogold-electron microscopy revealed HCN2 as the dominating subunit in cerebellar mossy fibers. Computational modeling indicated that HCN2 channels control conduction velocity primarily by altering the resting membrane potential and are associated with significant metabolic costs. These results suggest that the cAMP-HCN pathway provides neuromodulators with an opportunity to finely tune energy consumption and temporal delays across axons in the brain.

scholarly journals HCN channel-mediated neuromodulation can control action potential velocity and fidelity in central axons

2019 ◽  
Author(s):  
Niklas Byczkowicz ◽  
Abdelmoneim Eshra ◽  
Jacqueline Montanaro ◽  
Andrea Trevisiol ◽  
Johannes Hirrlinger ◽  
...  
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Mossy Fiber ◽  
Mossy Fibers ◽  
Adenosine Monophosphate ◽  
Resting Membrane Potential ◽  
Immunogold Electron Microscopy ◽  
Hcn Channels ◽  
Channel Blockers ◽  
Hcn Channel

AbstractHyperpolarization-activated cyclic-nucleotide-gated (HCN) channels control electrical rhythmicity and excitability in the heart and brain, but the function of HCN channels at subcellular level in axons remains poorly understood. Here, we show that the action potential conduction velocity in both myelinated and unmyelinated central axons can bidirectionally be modulated by HCN channel blockers, cyclic adenosine monophosphate (cAMP), and neuromodulators. Recordings from mice cerebellar mossy fiber boutons show that HCN channels ensure reliable high-frequency firing and are strongly modulated by cAMP (EC50 40 µM; estimated endogenous cAMP concentration 13 µM). In accord, immunogold-electron microscopy revealed HCN2 as the dominating subunit in cerebellar mossy fibers. Computational modeling indicated that HCN2 channels control conduction velocity primarily via altering the resting membrane potential and was associated with significant metabolic costs. These results suggest that the cAMP-HCN pathway provides neuromodulators an opportunity to finely tune energy consumption and temporal delays across axons in the brain.

scholarly journals High Threshold, Proximal Initiation, and Slow Conduction Velocity of Action Potentials in Dentate Granule Neuron Mossy Fibers

2008 ◽  
Vol 100 (1) ◽  
pp. 281-291 ◽  
Author(s):  
Geraldine J. Kress ◽  
Margaret J. Dowling ◽  
Julian P. Meeks ◽  
Steven Mennerick
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Action Potentials ◽  
Mossy Fiber ◽  
Hippocampal Slices ◽  
Mossy Fibers ◽  
Comparative Approach ◽  
Granule Neurons ◽  
Action Potential Initiation ◽  
Potential Initiation

Dentate granule neurons give rise to some of the smallest unmyelinated fibers in the mammalian CNS, the hippocampal mossy fibers. These neurons are also key regulators of physiological and pathophysiological information flow through the hippocampus. We took a comparative approach to studying mossy fiber action potential initiation and propagation in hippocampal slices from juvenile rats. Dentate granule neurons exhibited axonal action potential initiation significantly more proximal than CA3 pyramidal neurons. This conclusion was suggested by phase plot analysis of somatic action potentials and by local tetrodotoxin application to the axon and somatodendritic compartments. This conclusion was also verified by immunostaining for voltage-gated sodium channel alpha subunits and by direct dual soma/axonal recordings. Dentate neurons exhibited a significantly higher action potential threshold and slower axonal conduction velocity than CA3 neurons. We conclude that while the electrotonically proximal axon location of action potential initiation allows granule neurons to sensitively detect and integrate synaptic inputs, the neurons are sluggish to initiate and propagate an action potential.

scholarly journals Impact of Hyperpolarization-activated, Cyclic Nucleotide-gated Cation Channel Type 2 for the Xenon-mediated Anesthetic Effect

2015 ◽  
Vol 122 (5) ◽  
pp. 1047-1059 ◽  
Author(s):  
Corinna Mattusch ◽  
Stephan Kratzer ◽  
Martina Buerge ◽  
Matthias Kreuzer ◽  
Tatiana Engel ◽  
...  
Keyword(s):  
Brain Slices ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Signal Propagation ◽  
Network Activity ◽  
Hcn Channels ◽  
Kidney Cells ◽  
Hcn Channel ◽  
Human Embryonic Kidney ◽  
Human Embryonic Kidney Cells

Abstract Background: The thalamus is thought to be crucially involved in the anesthetic state. Here, we investigated the effect of the inhaled anesthetic xenon on stimulus-evoked thalamocortical network activity and on excitability of thalamocortical neurons. Because hyperpolarization-activated, cyclic nucleotide-gated cation (HCN) channels are key regulators of neuronal excitability in the thalamus, the effect of xenon on HCN channels was examined. Methods: The effects of xenon on thalamocortical network activity were investigated in acutely prepared brain slices from adult wild-type and HCN2 knockout mice by means of voltage-sensitive dye imaging. The influence of xenon on single-cell excitability in brain slices was investigated using the whole-cell patch-clamp technique. Effects of xenon on HCN channels were verified in human embryonic kidney cells expressing HCN2 channels. Results: Xenon concentration-dependently diminished thalamocortical signal propagation. In neurons, xenon reduced HCN channel-mediated Ih current amplitude by 33.4 ± 12.2% (at −133 mV; n = 7; P = 0.041) and caused a left-shift in the voltage of half-maximum activation (V1/2) from −98.8 ± 1.6 to −108.0 ± 4.2 mV (n = 8; P = 0.035). Similar effects were seen in human embryonic kidney cells. The impairment of HCN channel function was negligible when intracellular cyclic adenosine monophosphate level was increased. Using HCN2−/− mice, we could demonstrate that xenon did neither attenuate in vitro thalamocortical signal propagation nor did it show sedating effects in vivo. Conclusions: Here, we clearly showed that xenon impairs HCN2 channel function, and this impairment is dependent on intracellular cyclic adenosine monophosphate levels. We provide evidence that this effect reduces thalamocortical signal propagation and probably contributes to the hypnotic properties of xenon.

scholarly journals cAMP-dependent regulation of IKs single-channel kinetics

2017 ◽  
Vol 149 (8) ◽  
pp. 781-798 ◽  
Author(s):  
Emely Thompson ◽  
Jodene Eldstrom ◽  
Maartje Westhoff ◽  
Donald McAfee ◽  
Elise Balse ◽  
...  
Keyword(s):  
Action Potential ◽  
Single Channel ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Surface Expression ◽  
Voltage Sensor ◽  
Single Channels ◽  
Adrenergic Stimulation ◽  
Channel Opening ◽  
Sensor Activation

The delayed potassium rectifier current, IKs, is composed of KCNQ1 and KCNE1 subunits and plays an important role in cardiac action potential repolarization. During β-adrenergic stimulation, 3′-5′-cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) phosphorylates KCNQ1, producing an increase in IKs current and a shortening of the action potential. Here, using cell-attached macropatches and single-channel recordings, we investigate the microscopic mechanisms underlying the cAMP-dependent increase in IKs current. A membrane-permeable cAMP analog, 8-(4-chlorophenylthio)-cAMP (8-CPT-cAMP), causes a marked leftward shift of the conductance–voltage relation in macropatches, with or without an increase in current size. Single channels exhibit fewer silent sweeps, reduced first latency to opening (control, 1.61 ± 0.13 s; cAMP, 1.06 ± 0.11 s), and increased higher-subconductance-level occupancy in the presence of cAMP. The E160R/R237E and S209F KCNQ1 mutants, which show fixed and enhanced voltage sensor activation, respectively, largely abolish the effect of cAMP. The phosphomimetic KCNQ1 mutations, S27D and S27D/S92D, are much less and not at all responsive, respectively, to the effects of PKA phosphorylation (first latency of S27D + KCNE1 channels: control, 1.81 ± 0.1 s; 8-CPT-cAMP, 1.44 ± 0.1 s, P < 0.05; latency of S27D/S92D + KCNE1: control, 1.62 ± 0.1 s; cAMP, 1.43 ± 0.1 s, nonsignificant). Using total internal reflection fluorescence microscopy, we find no overall increase in surface expression of the channel during exposure to 8-CPT-cAMP. Our data suggest that the cAMP-dependent increase in IKs current is caused by an increase in the likelihood of channel opening, combined with faster openings and greater occupancy of higher subconductance levels, and is mediated by enhanced voltage sensor activation.

Ivabradine augments high-frequency dynamic gain of the heart rate response to low- and moderate-intensity vagal nerve stimulation under beta-blockade

2021 ◽  
Author(s):  
Toru Kawada ◽  
Hiromi Yamamoto ◽  
Kazunori Uemura ◽  
Yohsuke Hayama ◽  
Takuya Nishikawa ◽  
...  
Keyword(s):  
Heart Rate ◽  
Nerve Stimulation ◽  
High Frequency ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Vagal Nerve ◽  
Vagal Nerve Stimulation ◽  
Moderate Intensity ◽  
Beta Blockade ◽  
Hcn Channels

Our previous study indicated that intravenously administered ivabradine (IVA) augmented the dynamic heart rate (HR) response to moderate-intensity vagal nerve stimulation (VNS). Considering an accentuated antagonism, the results were somewhat paradoxical; i.e., the accentuated antagonism indicates that an activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels via the accumulation of intracellular cyclic adenosine monophosphate (cAMP) augments the HR response to VNS, whereas the inhibition of HCN channels by IVA also augmented the HR response to VNS. To remove the possible influence from the accentuated antagonism, we examined the effects of IVA on the dynamic vagal control of HR under beta-blockade. In anesthetized rats (n = 7), the right vagal nerve was stimulated for 10 min according to binary white noise signals between 0 and 10 Hz (V0-10), between 0 and 20 Hz (V0-20), and between 0 and 40 Hz (V0-40). The transfer function from VNS to HR was estimated. Under beta-blockade (propranolol, 2 mg/kg, i.v.), IVA (2 mg/kg, i.v.) did not augment the asymptotic low-frequency gain but increased the asymptotic high-frequency gain in V0-10 (0.53 ± 0.10 vs. 1.74 ± 0.40 beats·min−1·Hz−1, P < 0.01) and V0-20 (0.79 ± 0.14 vs. 2.06 ± 0.47 beats·min−1·Hz−1, P < 0.001). These changes, which were observed under a minimal influence from sympathetic background tone, may reflect an increased contribution of the acetylcholine-sensitive potassium channel (IK,ACh) pathway after IVA, because the HR control via the IK,ACh pathway is faster and acts in the frequency range higher than the cAMP-mediated pathway.

Immunological, biochemical, ultrastructural, and electrophysiological characteristics of a human glioblastoma-derived cell culture line

1982 ◽  
Vol 56 (1) ◽  
pp. 62-72 ◽  
Author(s):  
Peter McL. Black ◽  
Paul L. Kornblith ◽  
Peter F. Davison ◽  
Theodore M. Liszczak ◽  
Linda P. Merk ◽  
...  
Keyword(s):  
Cell Line ◽  
Surface Membrane ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Human Cell Line ◽  
Resting Membrane Potential ◽  
Content Type ◽  
Actin Cables ◽  
Fine Print

✓ This report presents the results of a study using multiple techniques of the established human cell line, LM, which has been developed in culture medium from a patient with a right temporoparietal glioblastoma. This cell line has human subtetraploid karyotype and has several features of a transformed line in culture. These include continuous propagation for 10 years, ability to form tumor nodules when transplanted into immunologically suppressed hamsters, and pleomorphic appearance. Ultrastructurally, it is characterized by multiple nuclei, few actin cables, and numerous surface-membrane microvilli, as well as abundant 9- to 10-nm cystoplasmic filaments. By its immunological reactivity, the line can be shown to contain glial fibrillary acidic protein at low levels, consistent with its glial origin and continued nature. Dibutyryl cyclic adenosine monophosphate (db-cAMP) induces formation of long astrocytic-like processes as well. Its membrane electrical characteristics include a low resting membrane potential and short time constant. Used in a microtiter antiglioma antibody cytotoxicity assay, LM yields a positive reaction to antibodies in the sera of 80% of patients with astrocytomas and only 9% of normal blood-bank donors, suggesting that it shares common antigens with other astrocytic tumor lines. The varied characteristics of this glioblastoma-derived line emphasize the “multiforme” nature of the neoplasm and suggest that for characterization of any such line, multiple parameters are necessary to allow comparison with other long-term glioblastoma lines in the literature. The usefulness of the LM line in in vitro cell biological, immunological, chemotherapeutic, and radiobiological studies of gliomas makes such efforts very worthwhile.

Changes in the electrophysiological properties of cat spinal motoneurons following the intramuscular injection of adriamycin compared with changes in the properties of motoneurons in aged cats

1995 ◽  
Vol 74 (5) ◽  
pp. 1972-1981 ◽  
Author(s):  
R. H. Liu ◽  
J. Yamuy ◽  
M. C. Xi ◽  
F. R. Morales ◽  
M. H. Chase
Keyword(s):  
Electrical Properties ◽  
Action Potential ◽  
Conduction Velocity ◽  
Time Constant ◽  
Correlation Coefficients ◽  
Input Resistance ◽  
Resting Membrane Potential ◽  
Electrophysiological Properties ◽  
Axonal Conduction ◽  
Adult Cat

1. This study was undertaken to investigate the effects of adriamycin (ADM, Doxorubicin) on the basic electrophysiological properties of spinal cord motoneurons in the adult cat. ADM was injected into the biceps, gastrocnemius, semitendinosus, and semimembranosus muscles of the left hindlimb (1.2 mg per muscle). Intracellular recordings from motoneurons innervating these muscles were carried out 12, 20, or 40 days after ADM administration and from corresponding motoneurons in untreated control cats. 2. Twelve days after ADM injection, motoneurons innervating ADM-treated muscles (ADM MNs) exhibited statistically significant increases in input resistance, membrane time constant, and amplitude of the action potential's afterhyperpolarization (AHP). In addition, there was a statistically significant decrease in rheobase and in the delay between the action potential of the initial segment (IS) and that of the somadendritic (SD) portion of the motoneuron (IS-SD delay). There were no significant changes in the resting membrane potential, threshold depolarization, action potential amplitude, or axonal conduction velocity. 3. The changes in electrical properties of motoneurons at 20 and 40 days after ADM injection were qualitatively similar to those observed at 12 days. However, at 40 days after ADM injection there was a statistically significant decrease in the axonal conduction velocity of the ADM MNs. 4. The normal correlations that are present between the AHP duration and electrical properties of the control motoneurons were observed in the ADM MNs, e.g., AHP duration was positively correlated with the input resistance and time constant and negatively correlated with the axonal conduction velocity. The correlation coefficients, however, were reduced in comparison with the control data. 5. This study demonstrates that ADM exerts significant effects on the electrical properties of motoneurons when injected into their target muscles. The majority of the changes in motoneuron electrical properties caused by ADM resemble those observed in motoneurons of aged cats. Additional research is required to determine whether the specific changes induced in motoneurons by ADM and those that occur in motoneurons in old age are due to similar degradative mechanisms.

scholarly journals All four subunits of HCN2 channels contribute to the activation gating in an additive but intricate manner

2018 ◽  
Vol 150 (9) ◽  
pp. 1261-1271 ◽  
Author(s):  
Mallikarjuna Rao Sunkara ◽  
Tina Schwabe ◽  
Gunter Ehrlich ◽  
Jana Kusch ◽  
Klaus Benndorf
Keyword(s):  
Cyclic Nucleotide ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Activation Mechanism ◽  
Hcn Channels ◽  
Binding Domains ◽  
Activation Gating ◽  
In Trans ◽  
In Cis ◽  
Special Case

Hyperpolarization-activated cyclic nucleotide–modulated (HCN) channels are tetramers that elicit electrical rhythmicity in specialized brain neurons and cardiomyocytes. The channels are dually activated by voltage and binding of cyclic adenosine monophosphate (cAMP) to their four cyclic nucleotide-binding domains (CNBDs). Here we analyze the effects of cAMP binding to different concatemers of HCN2 channel subunits, each having a defined number of functional CNBDs. We show that each liganded CNBD promotes channel activation in an additive manner and that, in the special case of two functional CNBDs, functionality does not depend on the arrangement of the subunits. Correspondingly, the reverse process of deactivation is slowed by progressive liganding, but only if four and three ligands as well as two ligands in trans position (opposite to each other) are bound. In contrast, two ligands bound in cis positions (adjacent to each other) and a single bound ligand do not affect channel deactivation. These results support an activation mechanism in which each single liganded CNBD causes a turning momentum on the tetrameric ring-like structure formed by all four CNBDs and that at least two liganded subunits in trans positions are required to maintain activation.

scholarly journals Inward Rectifier K + Currents Contribute to the Proarrhythmic Electrical Phenotype of Atria Overexpressing Cyclic Adenosine Monophosphate Response Element Modulator Isoform CREM‐IbΔC‐X

2020 ◽  
Vol 9 (23) ◽  
Author(s):  
Florentina Pluteanu ◽  
Matthias D. Seidl ◽  
Sabine Hamer ◽  
Beatrix Scholz ◽  
Frank U. Müller
Keyword(s):  
Action Potential ◽  
Outward Current ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Inward Rectifier ◽  
Mrna Levels ◽  
Wild Type ◽  
Atrial Myocytes ◽  
Response Element ◽  
Repolarization Reserve

BACKGROUND Transgenic mice (TG) with heart‐directed overexpresion of the isoform of the transcription factor cyclic adenosine monophosphate response element modulator (CREM), CREM‐IbΔC‐X, display spontaneous atrial fibrillation (AF) and action potential prolongation. The remodeling of the underlying ionic currents remains unknown. Here, we investigated the regulatory role of CREM‐IbΔC‐X on the expression of K + channel subunits and the corresponding K + currents in relation to AF onset in TG atrial myocytes. METHODS AND RESULTS ECG recordings documented the absence or presence of AF in 6‐week‐old (before AF onset) and 12‐week‐old TG (after AF onset) and wild‐type littermate mice before atria removal to perform patch clamp, contractility, and biochemical experiments. In TG atrial myocytes, we found reduced repolarization reserve K + currents attributed to a decrease of transiently outward current and inward rectifier K + current with phenotype progression, and of acetylcholine‐activated K + current, age independent. The molecular determinants of these changes were lower mRNA levels of Kcnd2/3 , Kcnip2 , Kcnj2/4 , and Kcnj3/5 and decreased protein levels of K + channel interacting protein 2 (KChIP2 ), Kir2.1/3, and Kir3.1/4, respectively. After AF onset, inward rectifier K + current contributed less to action potential repolarization, in line with the absence of outward current component, whereas the acetylcholine‐induced action potential shortening before AF onset (6‐week‐old TG mice) was smaller than in wild‐type and 12‐week‐old TG mice. Atrial force of contraction measured under combined vagal‐sympathetic stimulation revealed increased sensitivity to isoprenaline irrespective of AF onset in TG. Moreover, we identified Kcnd2 , Kcnd3 , Kcnj3 , and Kcnh2 as novel CREM‐target genes. CONCLUSIONS Our study links the activation of cyclic adenosine monophosphate response element–mediated transcription to the proarrhythmogenic electrical remodeling of atrial inward rectifier K + currents with a role in action potential duration, resting membrane stability, and vagal control of the electrical activity.

scholarly journals The HCN Channel Voltage Sensor Undergoes A Large Downward Motion During Hyperpolarization

2019 ◽  
Author(s):  
Gucan Dai ◽  
Teresa K. Aman ◽  
Frank DiMaio ◽  
William N. Zagotta
Keyword(s):  
Ion Channels ◽  
Metal Ion ◽  
Voltage Sensor ◽  
The Body ◽  
Resting Membrane Potential ◽  
Hcn Channels ◽  
Hcn Channel ◽  
Open Probability ◽  
Membrane Hyperpolarization ◽  
Transmembrane Voltage

Voltage-gated ion channels (VGICs) underlie almost all electrical signaling in the body1. They change their open probability in response to changes in transmembrane voltage, allowing permeant ions to flow across the cell membrane. Ion flow through VGICs underlies numerous physiological processes in excitable cells1. In particular, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which operate at the threshold of excitability, are essential for pacemaking activity, resting membrane potential, and synaptic integration2. VGICs contain a series of positively-charged residues that are displaced in response to changes in transmembrane voltage, resulting in a conformational change that opens the pore3–6. These voltage-sensing charges, which reside in the S4 transmembrane helix of the voltage-sensor domain (VSD)3 and within the membrane’s electric field, are thought to move towards the inside of the cell (downwards) during membrane hyperpolarization7. HCN channels are unique among VGICs because their open probability is increased by membrane hyperpolarization rather than depolarization8–10. The mechanism underlying this “reverse gating” is still unclear. Moreover, although many X-ray crystal and cryo-EM structures have been solved for the depolarized state of the VSD, including that of HCN channels11, no structures have been solved at hyperpolarized voltages. Here we measure the precise movement of the charged S4 helix of an HCN channel using transition metal ion fluorescence resonance energy transfer (tmFRET). We show that the S4 undergoes a significant (~10 Å) downward movement in response to membrane hyperpolarization. Furthermore, by applying constraints determined from tmFRET experiments to Rosetta modeling, we reveal that the carboxyl-terminal part of the S4 helix exhibits an unexpected tilting motion during hyperpolarization activation. These data provide a long-sought glimpse of the hyperpolarized state of a functioning VSD and also a framework for understanding the dynamics of reverse gating in HCN channels. Our methods can be broadly applied to probe short-distance rearrangements in other ion channels and membrane proteins.

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