1
|
Verkerk AO, Wilders R. The Action Potential Clamp Technique as a Tool for Risk Stratification of Sinus Bradycardia Due to Loss-of-Function Mutations in HCN4: An In Silico Exploration Based on In Vitro and In Vivo Data. Biomedicines 2023; 11:2447. [PMID: 37760888 PMCID: PMC10525944 DOI: 10.3390/biomedicines11092447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Revised: 08/30/2023] [Accepted: 08/31/2023] [Indexed: 09/29/2023] Open
Abstract
These days, in vitro functional analysis of gene variants is becoming increasingly important for risk stratification of cardiac ion channelopathies. So far, such risk stratification has been applied to SCN5A, KCNQ1, and KCNH2 gene variants associated with Brugada syndrome and long QT syndrome types 1 and 2, respectively, but risk stratification of HCN4 gene variants related to sick sinus syndrome has not yet been performed. HCN4 is the gene responsible for the hyperpolarization-activated 'funny' current If, which is an important modulator of the spontaneous diastolic depolarization underlying the sinus node pacemaker activity. In the present study, we carried out a risk classification assay on those loss-of-function mutations in HCN4 for which in vivo as well as in vitro data have been published. We used the in vitro data to compute the charge carried by If (Qf) during the diastolic depolarization phase of a prerecorded human sinus node action potential waveform and assessed the extent to which this Qf predicts (1) the beating rate of the comprehensive Fabbri-Severi model of a human sinus node cell with mutation-induced changes in If and (2) the heart rate observed in patients carrying the associated mutation in HCN4. The beating rate of the model cell showed a very strong correlation with Qf from the simulated action potential clamp experiments (R2 = 0.95 under vagal tone). The clinically observed minimum or resting heart rates showed a strong correlation with Qf (R2 = 0.73 and R2 = 0.71, respectively). While a translational perspective remains to be seen, we conclude that action potential clamp on transfected cells, without the need for further voltage clamp experiments and data analysis to determine individual biophysical parameters of If, is a promising tool for risk stratification of sinus bradycardia due to loss-of-function mutations in HCN4. In combination with an If blocker, this tool may also prove useful when applied to human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) obtained from mutation carriers and non-carriers.
Collapse
Affiliation(s)
- Arie O. Verkerk
- Department of Medical Biology, Amsterdam Cardiovascular Sciences, Amsterdam UMC, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands;
- Department of Experimental Cardiology, Heart Center, Amsterdam Cardiovascular Sciences, Amsterdam UMC, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
| | - Ronald Wilders
- Department of Medical Biology, Amsterdam Cardiovascular Sciences, Amsterdam UMC, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands;
| |
Collapse
|
2
|
Hu W, Clark RB, Giles WR, Kondo C, Zhang H. Frequency-Dependent Properties of the Hyperpolarization-Activated Cation Current, I f, in Adult Mouse Heart Primary Pacemaker Myocytes. Int J Mol Sci 2022; 23:4299. [PMID: 35457119 DOI: 10.3390/ijms23084299] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 04/05/2022] [Accepted: 04/11/2022] [Indexed: 02/04/2023] Open
Abstract
A number of distinct electrophysiological mechanisms that modulate the myogenic spontaneous pacemaker activity in the sinoatrial node (SAN) of the mammalian heart have been investigated extensively. There is agreement that several (3 or 4) different transmembrane ionic current changes (referred to as the voltage clock) are involved; and that the resulting net current interacts with direct and indirect effects of changes in intracellular Ca2+ (the calcium clock). However, significant uncertainties, and important knowledge gaps, remain concerning the functional roles in SAN spontaneous pacing of many of the individual ion channel- or exchanger-mediated transmembrane current changes. We report results from patch clamp studies and mathematical modeling of the hyperpolarization-activated current, If, in the generation/modulation of the diastolic depolarization, or pacemaker potential, produced by individual myocytes that were enzymatically isolated from the adult mouse sinoatrial node (SAN). Amphotericin-mediated patch microelectrode recordings at 35 °C were made under control conditions and in the presence of 5 or 10 nM isoproterenol (ISO). These sets of results were complemented and integrated with mathematical modeling of the current changes that take place in the range of membrane potentials (−70 to −50 mV), which corresponds to the ‘pacemaker depolarization’ in the adult mouse SAN. Our results reveal a very small, but functionally important, approximately steady-state or time-independent current generated by residual activation of If channels that are expressed in these pacemaker myocytes. Recordings of the pacemaker depolarization and action potential, combined with measurements of changes in If, and the well-known increases in the L-type Ca2+ current, ICaL, demonstrated that ICaL activation, is essential for myogenic pacing. Moreover, after being enhanced (approximately 3-fold) by 5 or 10 nM ISO, ICaL contributes significantly to the positive chronotropic effect. Our mathematical model has been developed in an attempt to better understand the underlying mechanisms for the pacemaker depolarization and action potential in adult mouse SAN myocytes. After being updated with our new experimental data describing If, our simulations reveal a novel functional component of If in adult mouse SAN. Computational work carried out with this model also confirms that in the presence of ISO the residual activation of If and opening of ICaL channels combine to generate a net current change during the slow diastolic depolarization phase that is essential for the observed accelerated pacemaking rate of these SAN myocytes.
Collapse
|
3
|
Abstract
Pacemaker cells are the basis of rhythm in the heart. Cardiovascular diseases, and in particular, arrhythmias are a leading cause of hospital admissions and have been implicated as a cause of sudden death. The prevalence of people with arrhythmias will increase in the next years due to an increase in the ageing population and risk factors. The current therapies are limited, have a lot of side effects, and thus, are not ideal. Pacemaker channels, also called hyperpolarizationactivated cyclic nucleotide-gated (HCN) channels, are the molecular correlate of the hyperpolarization- activated current, called Ih (from hyperpolarization) or If (from funny), that contribute crucially to the pacemaker activity in cardiac nodal cells and impulse generation and transmission in neurons. HCN channels have emerged as interesting targets for the development of drugs, in particular, to lower the heart rate. Nonetheless, their pharmacology is still rather poorly explored in comparison to many other voltage-gated ion channels or ligand-gated ion channels. Ivabradine is the first and currently the only clinically approved compound that specifically targets HCN channels. The therapeutic indication of ivabradine is the symptomatic treatment of chronic stable angina pectoris in patients with coronary artery disease with a normal sinus rhythm. Several other pharmacological agents have been shown to exert an effect on heart rate, although this effect is not always desired. This review is focused on the pacemaking process taking place in the heart and summarizes the current knowledge on HCN channels.
Collapse
Affiliation(s)
- Anne-Sophie Depuydt
- Toxicology and Pharmacology, University of Leuven (KU Leuven), Campus Gasthuisberg, O&N2, PO Box 922, Herestraat 49, 3000Leuven, Belgium
| | - Steve Peigneur
- Toxicology and Pharmacology, University of Leuven (KU Leuven), Campus Gasthuisberg, O&N2, PO Box 922, Herestraat 49, 3000Leuven, Belgium
| | - Jan Tytgat
- Toxicology and Pharmacology, University of Leuven (KU Leuven), Campus Gasthuisberg, O&N2, PO Box 922, Herestraat 49, 3000Leuven, Belgium
| |
Collapse
|
4
|
Dewar MB. HCN3 has minimal involvement in the sensation of acute, inflammatory and neuropathic pain. J Physiol 2019; 597:5333-5334. [PMID: 31549390 DOI: 10.1113/jp278770] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Accepted: 09/20/2019] [Indexed: 11/08/2022] Open
|
5
|
Ziyatdinova NI, Kuptsova AM, Faskhutdinov LI, Galieva AM, Zefirov AL, Zefirov TL. Effect of If Current Blockade on Newborn Rat Heart Isolated According to Langendorff. Bull Exp Biol Med 2019; 167:424-427. [PMID: 31529169 DOI: 10.1007/s10517-019-04541-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Indexed: 01/09/2023]
Abstract
The study examined the effects of hyperpolarization-activated funny current (If) on HR and coronary flow in Langendorff-isolated hearts from newborn rats. Blockade of If current with ZD7288 changed the examined cardiac parameters. The blocker in a concentration of 10-9 M decreased HR by 26.8% (p≤0.05). In concentrations 10-8, 10-7, 10-6, and 10-5 M ZD7288 produced minor differently directed effects. In a concentration of 10-5 M, ZD7288 reduced coronary flow in the isolated heart (p≤0.01). In other concentrations, the blocker produced no significant effects on coronary flow.
Collapse
Affiliation(s)
- N I Ziyatdinova
- Department of Human Health Protection, Kazan (Volga region) Federal University, Kazan, Russia
| | - A M Kuptsova
- Department of Human Health Protection, Kazan (Volga region) Federal University, Kazan, Russia
| | - L I Faskhutdinov
- Department of Human Health Protection, Kazan (Volga region) Federal University, Kazan, Russia
| | - A M Galieva
- Department of Human Health Protection, Kazan (Volga region) Federal University, Kazan, Russia
| | - A L Zefirov
- Department of Normal Physiology, Kazan Federal Medical University, Kazan, the republic of Tatarstan, Russia
| | - T L Zefirov
- Department of Human Health Protection, Kazan (Volga region) Federal University, Kazan, Russia.
| |
Collapse
|
6
|
Dini L, Del Lungo M, Resta F, Melchiorre M, Spinelli V, Di Cesare Mannelli L, Ghelardini C, Laurino A, Sartiani L, Coppini R, Mannaioni G, Cerbai E, Romanelli MN. Selective Blockade of HCN1/HCN2 Channels as a Potential Pharmacological Strategy Against Pain. Front Pharmacol 2018; 9:1252. [PMID: 30467478 PMCID: PMC6237106 DOI: 10.3389/fphar.2018.01252] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 10/15/2018] [Indexed: 12/25/2022] Open
Abstract
A prominent role of hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels has been suggested based on their expression and (dys)function in dorsal root ganglion (DRG) neurons, being likely involved in peripheral nociception. Using HCN blockers as antinociceptive drugs is prevented by the widespread distribution of these channels. However, tissue-specific expression of HCN isoforms varies significantly, HCN1 and HCN2 being considered as major players in DRG excitability. We characterized the pharmacological effect of a novel compound, MEL55A, able to block selectively HCN1/HCN2 isoforms, on DRG neuron excitability in-vitro and for its antiallodynic properties in-vivo. HEK293 cells expressing HCN1, HCN2, or HCN4 isoforms were used to verify drug selectivity. The pharmacological profile of MEL55A was tested on mouse DRG neurons by patch-clamp recordings, and in-vivo in oxaliplatin-induced neuropathy by means of thermal hypersensitivity. Results were compared to the non-isoform-selective drug, ivabradine. MEL55A showed a marked preference toward HCN1 and HCN2 isoforms expressed in HEK293, with respect to HCN4. In cultured DRG, MEL55A reduced I h amplitude, both in basic conditions and after stimulation by forskolin, and cell excitability, its effect being quantitatively similar to that observed with ivabradine. MEL55A was able to relieve chemotherapy-induced neuropathic pain. In conclusion, selective blockade of HCN1/HCN2 channels, over HCN4 isoform, was able to modulate electrophysiological properties of DRG neurons similarly to that reported for classical I h blockers, ivabradine, resulting in a pain-relieving activity. The availability of small molecules with selectivity toward HCN channel isoforms involved in nociception might represent a safe and effective strategy against chronic pain.
Collapse
Affiliation(s)
- Leonardo Dini
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Martina Del Lungo
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Francesco Resta
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Michele Melchiorre
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Valentina Spinelli
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Lorenzo Di Cesare Mannelli
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Carla Ghelardini
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Annunziatina Laurino
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Laura Sartiani
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Raffaele Coppini
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Guido Mannaioni
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Elisabetta Cerbai
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| | - Maria Novella Romanelli
- Department of Neurosciences, Psychology, Drug Research and Child Health (NeuroFarBa), University of Florence, Florence, Italy
| |
Collapse
|
7
|
Zhao Z, Li L, Gu H. Dynamical Mechanism of Hyperpolarization-Activated Non-specific Cation Current Induced Resonance and Spike-Timing Precision in a Neuronal Model. Front Cell Neurosci 2018; 12:62. [PMID: 29568262 PMCID: PMC5852126 DOI: 10.3389/fncel.2018.00062] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Accepted: 02/20/2018] [Indexed: 01/23/2023] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated cation current (Ih) plays important roles in the achievement of many physiological/pathological functions in the nervous system by modulating the electrophysiological activities, such as the rebound (spike) to hyperpolarization stimulations, subthreshold membrane resonance to sinusoidal currents, and spike-timing precision to stochastic factors. In the present paper, with increasing gh (conductance of Ih), the rebound (spike) and subthreshold resonance appear and become stronger, and the variability of the interspike intervals (ISIs) becomes lower, i.e., the enhancement of spike-timing precision, which are simulated in a conductance-based theoretical model and well explained by the nonlinear concept of bifurcation. With increasing gh, the stable node to stable focus, to coexistence behavior, and to firing via the codimension-1 bifurcations (Hopf bifurcation, saddle-node bifurcation, saddle-node bifurcations on an invariant circle, and saddle homoclinic orbit) and codimension-2 bifurcations such as Bogdanov-Takens (BT) point related to the transition between saddle-node and Hopf bifurcations, are acquired with 1- and 2-parameter bifurcation analysis. The decrease of variability of ISIs with increasing gh is induced by the fast decrease of the standard deviation of ISIs, which is related to the increase of the capacity of resisting noisy disturbance due to the firing becomes far away from the bifurcation point. The enhancement of the rebound (spike) with increasing gh builds up a relationship to the decrease of the capacity of resisting disturbance like the hyperpolarization stimulus as the resting state approaches the bifurcation point. The “typical”-resonance and non-resonance appear in the parameter region of the stable focus and node far away from the bifurcation points, respectively. The complex or “strange” dynamics, such as the “weak”-resonance for the stable node near the transition point between the stable node and focus and the non-resonance for the stable focus close to the codimension-1 and −2 bifurcation points, are discussed.
Collapse
Affiliation(s)
- Zhiguo Zhao
- School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai, China.,School of Basic Science, Henan Institute of Technology, Xinxiang, China
| | - Li Li
- School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai, China
| | - Huaguang Gu
- School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai, China
| |
Collapse
|
8
|
Garden DLF, Oostland M, Jelitai M, Rinaldi A, Duguid I, Nolan MF. Inferior Olive HCN1 Channels Coordinate Synaptic Integration and Complex Spike Timing. Cell Rep 2018; 22:1722-1733. [PMID: 29444426 PMCID: PMC5847187 DOI: 10.1016/j.celrep.2018.01.069] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 01/03/2018] [Accepted: 01/22/2018] [Indexed: 02/07/2023] Open
Abstract
Cerebellar climbing-fiber-mediated complex spikes originate from neurons in the inferior olive (IO), are critical for motor coordination, and are central to theories of cerebellar learning. Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels expressed by IO neurons have been considered as pacemaker currents important for oscillatory and resonant dynamics. Here, we demonstrate that in vitro, network actions of HCN1 channels enable bidirectional glutamatergic synaptic responses, while local actions of HCN1 channels determine the timing and waveform of synaptically driven action potentials. These roles are distinct from, and may complement, proposed pacemaker functions of HCN channels. We find that in behaving animals HCN1 channels reduce variability in the timing of cerebellar complex spikes, which serve as a readout of IO spiking. Our results suggest that spatially distributed actions of HCN1 channels enable the IO to implement network-wide rules for synaptic integration that modulate the timing of cerebellar climbing fiber signals. HCN1 channels in IO neurons control synaptic response and spiking activity Network actions of HCN1 channels enable bidirectional synaptic responses Local actions of HCN1 channels control spike timing and spikelet number In awake mice, HCN1 channels reduce timing variability of cerebellar complex spikes
Collapse
Affiliation(s)
- Derek L F Garden
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Marlies Oostland
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Marta Jelitai
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Arianna Rinaldi
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Ian Duguid
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK; Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Matthew F Nolan
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK; Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh EH8 9XD, UK.
| |
Collapse
|
9
|
Xu K, Maidana JP, Caviedes M, Quero D, Aguirre P, Orio P. Hyperpolarization-Activated Current Induces Period-Doubling Cascades and Chaos in a Cold Thermoreceptor Model. Front Comput Neurosci 2017; 11:12. [PMID: 28344550 PMCID: PMC5344906 DOI: 10.3389/fncom.2017.00012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Accepted: 02/24/2017] [Indexed: 11/13/2022] Open
Abstract
In this article, we describe and analyze the chaotic behavior of a conductance-based neuronal bursting model. This is a model with a reduced number of variables, yet it retains biophysical plausibility. Inspired by the activity of cold thermoreceptors, the model contains a persistent Sodium current, a Calcium-activated Potassium current and a hyperpolarization-activated current (Ih) that drive a slow subthreshold oscillation. Driven by this oscillation, a fast subsystem (fast Sodium and Potassium currents) fires action potentials in a periodic fashion. Depending on the parameters, this model can generate a variety of firing patterns that includes bursting, regular tonic and polymodal firing. Here we show that the transitions between different firing patterns are often accompanied by a range of chaotic firing, as suggested by an irregular, non-periodic firing pattern. To confirm this, we measure the maximum Lyapunov exponent of the voltage trajectories, and the Lyapunov exponent and Lempel-Ziv's complexity of the ISI time series. The four-variable slow system (without spiking) also generates chaotic behavior, and bifurcation analysis shows that this is often originated by period doubling cascades. Either with or without spikes, chaos is no longer generated when the Ih is removed from the system. As the model is biologically plausible with biophysically meaningful parameters, we propose it as a useful tool to understand chaotic dynamics in neurons.
Collapse
Affiliation(s)
- Kesheng Xu
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Jean P Maidana
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Mauricio Caviedes
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso Valparaíso, Chile
| | - Daniel Quero
- Departamento de Matemática, Universidad Técnica Federico Santa María Valparaíso, Chile
| | - Pablo Aguirre
- Departamento de Matemática, Universidad Técnica Federico Santa María Valparaíso, Chile
| | - Patricio Orio
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de ValparaísoValparaíso, Chile; Facultad de Ciencias, Instituto de Neurociencia, Universidad de ValparaísoValparaíso, Chile
| |
Collapse
|
10
|
Huang YY, Liu YC, Lee CT, Lin YC, Wang ML, Yang YP, Chang KY, Chiou SH. Revisiting the Lamotrigine-Mediated Effect on Hippocampal GABAergic Transmission. Int J Mol Sci 2016; 17:E1191. [PMID: 27455251 DOI: 10.3390/ijms17071191] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 07/19/2016] [Indexed: 01/07/2023] Open
Abstract
Lamotrigine (LTG) is generally considered as a voltage-gated sodium (Nav) channel blocker. However, recent studies suggest that LTG can also serve as a hyperpolarization-activated cyclic nucleotide-gated (HCN) channel enhancer and can increase the excitability of GABAergic interneurons (INs). Perisomatic inhibitory INs, predominantly fast-spiking basket cells (BCs), powerfully inhibit granule cells (GCs) in the hippocampal dentate gyrus. Notably, BCs express abundant Nav channels and HCN channels, both of which are able to support sustained action potential generation. Using whole-cell recording in rat hippocampal slices, we investigated the net LTG effect on BC output. We showed that bath application of LTG significantly decreased the amplitude of evoked compound inhibitory postsynaptic currents (IPSCs) in GCs. In contrast, simultaneous paired recordings from BCs to GCs showed that LTG had no effect on both the amplitude and the paired-pulse ratio of the unitary IPSCs, suggesting that LTG did not affect GABA release, though it suppressed cell excitability. In line with this, LTG decreased spontaneous IPSC (sIPSC) frequency, but not miniature IPSC frequency. When re-examining the LTG effect on GABAergic transmission in the cornus ammonis region 1 (CA1) area, we found that LTG markedly inhibits both the excitability of dendrite-targeting INs in the stratum oriens and the concurrent sIPSCs recorded on their targeting pyramidal cells (PCs) without significant hyperpolarization-activated current (Ih) enhancement. In summary, LTG has no effect on augmenting Ih in GABAergic INs and does not promote GABAergic inhibitory output. The antiepileptic effect of LTG is likely through Nav channel inhibition and the suppression of global neuronal network activity.
Collapse
|
11
|
Caspari F, Baumann VJ, Garcia-Pino E, Koch U. Heterogeneity of Intrinsic and Synaptic Properties of Neurons in the Ventral and Dorsal Parts of the Ventral Nucleus of the Lateral Lemniscus. Front Neural Circuits 2015; 9:74. [PMID: 26635535 PMCID: PMC4649059 DOI: 10.3389/fncir.2015.00074] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 10/30/2015] [Indexed: 11/13/2022] Open
Abstract
The ventral nucleus of the lateral lemniscus (VNLL) provides a major inhibitory projection to the inferior colliculus (IC). Neurons in the VNLL respond with various firing patterns and different temporal precision to acoustic stimulation. The present study investigates the underlying intrinsic and synaptic properties of various cell types in different regions of the VNLL, using in vitro electrophysiological recordings from acute brain slices of mice and immunohistochemistry. We show that the biophysical membrane properties and excitatory input characteristics differed between dorsal and ventral VNLL neurons. Neurons in the ventral VNLL displayed an onset-type firing pattern and little hyperpolarization-activated current (Ih). Stimulation of lemniscal inputs evoked a large all-or-none excitatory response similar to Calyx of Held synapses in neurons in the lateral part of the ventral VNLL. Neurons that were located within the fiber tract of the lateral lemniscus, received several and weak excitatory input fibers. In the dorsal VNLL onset-type and sustained firing neurons were intermingled. These neurons showed large Ih and were strongly immunopositive for the hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1) subunit. Both neuron types received several excitatory inputs that were weaker and slower compared to ventrolateral VNLL neurons. Using a mouse model that expresses channelrhodopsin under the promotor of the vesicular GABA transporter (VGAT) suggests that dorsal and ventral neurons were inhibitory since they were all depolarized by light stimulation. The diverse membrane and input properties in dorsal and ventral VNLL neurons suggest differential roles of these neurons for sound processing.
Collapse
Affiliation(s)
- Franziska Caspari
- Neurophysiology, Institute of Biology, Freie Universität Berlin Berlin, Germany
| | - Veronika J Baumann
- Neurophysiology, Institute of Biology, Freie Universität Berlin Berlin, Germany
| | | | - Ursula Koch
- Neurophysiology, Institute of Biology, Freie Universität Berlin Berlin, Germany
| |
Collapse
|
12
|
Santin JM, Hartzler LK. Activation state of the hyperpolarization-activated current modulates temperature-sensitivity of firing in locus coeruleus neurons from bullfrogs. Am J Physiol Regul Integr Comp Physiol 2015; 308:R1045-61. [PMID: 25833936 DOI: 10.1152/ajpregu.00036.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 03/30/2015] [Indexed: 12/18/2022]
Abstract
Locus coeruleus neurons of anuran amphibians contribute to breathing control and have spontaneous firing frequencies that, paradoxically, increase with cooling. We previously showed that cooling inhibits a depolarizing membrane current, the hyperpolarization-activated current (I h) in locus coeruleus neurons from bullfrogs, Lithobates catesbeianus (Santin JM, Watters KC, Putnam RW, Hartzler LK. Am J Physiol Regul Integr Comp Physiol 305: R1451-R1464, 2013). This suggests an unlikely role for I h in generating cold activation, but led us to hypothesize that inhibition of I h by cooling functions as a physiological brake to limit the cold-activated response. Using whole cell electrophysiology in brain slices, we employed 2 mM Cs(+) (an I h antagonist) to isolate the role of I h in spontaneous firing and cold activation in neurons recorded with either control or I h agonist (cyclic AMP)-containing artificial intracellular fluid. I h did not contribute to the membrane potential (V m) and spontaneous firing at 20°C. Although voltage-clamp analysis confirmed that cooling inhibits I h, its lack of involvement in setting baseline firing and V m precluded its ability to regulate cold activation as hypothesized. In contrast, neurons dialyzed with cAMP exhibited greater baseline firing frequencies at 20°C due to I h activation. Our hypothesis was supported when the starting level of I h was enhanced by elevating cAMP because cold activation was converted to more ordinary cold inhibition. These findings indicate that situations leading to enhancement of I h facilitate firing at 20°C, yet the hyperpolarization associated with inhibiting a depolarizing cation current by cooling blunts the net V m response to cooling to oppose normal cold-depolarizing factors. This suggests that the influence of I h activation state on neuronal firing varies in the poikilothermic neuronal environment.
Collapse
Affiliation(s)
- Joseph M Santin
- Department of Biological Sciences, Wright State University, Dayton, Ohio
| | - Lynn K Hartzler
- Department of Biological Sciences, Wright State University, Dayton, Ohio
| |
Collapse
|
13
|
Verkerk AO, Wilders R. Pacemaker activity of the human sinoatrial node: an update on the effects of mutations in HCN4 on the hyperpolarization-activated current. Int J Mol Sci 2015; 16:3071-94. [PMID: 25642760 PMCID: PMC4346881 DOI: 10.3390/ijms16023071] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 01/22/2015] [Indexed: 11/22/2022] Open
Abstract
Since 2003, several loss-of-function mutations in the HCN4 gene, which encodes the HCN4 protein, have been associated with sinus node dysfunction. In human sinoatrial node (SAN), HCN4 is the most abundant of the four isoforms of the HCN family. Tetramers of HCN subunits constitute the ion channels that conduct the hyperpolarization-activated "funny" current (If), which plays an important modulating role in SAN pacemaker activity. Voltage-clamp experiments on HCN4 channels expressed in COS-7, CHO and HEK-293 cells, as well as in Xenopus oocytes have revealed changes in the expression and kinetics of mutant channels, but the extent to which especially the kinetic changes would affect If flowing during a human SAN action potential often remains unresolved. In our contribution to the Topical Collection on Human Single Nucleotide Polymorphisms and Disease Diagnostics, we provide an updated review of the mutation-induced changes in the expression and kinetics of HCN4 channels and provide an overview of their effects on If during the time course of a human SAN action potential, as assessed in simulated action potential clamp experiments. Future research may solve apparent inconsistencies between data from clinical studies and data from in vitro and in silico experiments.
Collapse
Affiliation(s)
- Arie O Verkerk
- Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
| | - Ronald Wilders
- Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
| |
Collapse
|
14
|
Yoshimoto R, Iwasaki S, Takago H, Nakajima T, Sahara Y, Kitamura K. Developmental increase in hyperpolarization-activated current regulates intrinsic firing properties in rat vestibular ganglion cells. Neuroscience 2014; 284:632-642. [PMID: 25450961 DOI: 10.1016/j.neuroscience.2014.10.034] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Revised: 10/21/2014] [Accepted: 10/22/2014] [Indexed: 12/22/2022]
Abstract
The primary vestibular neurons convey afferent information from hair cells in the inner ear to the vestibular nuclei and the cerebellum. The intrinsic firing properties of vestibular ganglion cells (VGCs) are heterogeneous to sustained membrane depolarization, and undergo marked developmental changes from phasic to tonic types during the early postnatal period. Previous studies have shown that low-voltage-activated potassium channels, Kv1 and Kv7, play a critical role in determining the firing pattern of VGCs. In the present study, we explored the developmental changes in the properties of hyperpolarization-activated current (Ih) in rat VGCs and the role played by Ih in determining the firing properties of VGCs. Tonic firing VGCs showed a larger current density of Ih as compared to phasic firing VGCs, and tonic firing VGCs became phasic firing in the presence of ZD7288, an Ih channel blocker, indicating that Ih contributes to control the firing pattern of VGCs. The amplitude of Ih increased and the activation kinetics of Ih became faster during the developmental period. Analysis of developmental changes in the expression of hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels revealed that expression of HCN1 protein and its mRNA increased during the developmental period, whereas expression of HCN2-4 protein and its mRNA did not change. Our results suggest that HCN1 channels as well as Kv1 channels are critical in determining the firing pattern of rat VGCs and that developmental up-regulation of HCN1 transforms VGCs from phasic to tonic firing phenotypes.
Collapse
Affiliation(s)
- R Yoshimoto
- Department of Otolaryngology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
| | - S Iwasaki
- Department of Otolaryngology, Faculty of Medicine, University of Tokyo, Tokyo, Japan.
| | - H Takago
- Department of Rehabilitation for Sensory Functions, Research Institute, National Rehabilitation Center for Persons with Disabilities, Saitama, Japan
| | - T Nakajima
- Department of Circular Physiology, Faculty of Medicine, University of Tokyo, Tokyo, Japan
| | - Y Sahara
- Department of Physiology, Iwate Medical University, School of Dentistry, Iwate, Japan
| | - K Kitamura
- Department of Otolaryngology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
| |
Collapse
|
15
|
Needham K, Hyakumura T, Gunewardene N, Dottori M, Nayagam BA. Electrophysiological properties of neurosensory progenitors derived from human embryonic stem cells. Stem Cell Res 2013; 12:241-9. [PMID: 24280418 DOI: 10.1016/j.scr.2013.10.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Revised: 10/30/2013] [Accepted: 10/30/2013] [Indexed: 01/19/2023] Open
Abstract
In severe cases of sensorineural hearing loss where the numbers of auditory neurons are significantly depleted, stem cell-derived neurons may provide a potential source of replacement cells. The success of such a therapy relies upon producing a population of functional neurons from stem cells, to enable precise encoding of sound information to the brainstem. Using our established differentiation assay to produce sensory neurons from human stem cells, patch-clamp recordings indicated that all neurons examined generated action potentials and displayed both transient sodium and sustained potassium currents. Stem cell-derived neurons reliably entrained to stimuli up to 20 pulses per second (pps), with 50% entrainment at 50 pps. A comparison with cultured primary auditory neurons indicated similar firing precision during low-frequency stimuli, but significant differences after 50 pps due to differences in action potential latency and width. The firing properties of stem cell-derived neurons were also considered relative to time in culture (31-56 days) and revealed no change in resting membrane potential, threshold or firing latency over time. Thus, while stem cell-derived neurons did not entrain to high frequency stimulation as effectively as mammalian auditory neurons, their electrical phenotype was stable in culture and consistent with that reported for embryonic auditory neurons.
Collapse
Affiliation(s)
- Karina Needham
- Department of Otolaryngology, University of Melbourne, Royal Victorian Eye and Ear Hospital, Level 2, 32 Gisborne Street, East Melbourne, VIC 3002, Australia; Department of Medicine, St Vincent's Hospital, University of Melbourne, Level 4, Clinical Sciences Building, 29 Regent Street, Fitzroy, VIC 3065, Australia.
| | - Tomoko Hyakumura
- Department of Otolaryngology, University of Melbourne, Royal Victorian Eye and Ear Hospital, Level 2, 32 Gisborne Street, East Melbourne, VIC 3002, Australia.
| | - Niliksha Gunewardene
- Department of Otolaryngology, University of Melbourne, Royal Victorian Eye and Ear Hospital, Level 2, 32 Gisborne Street, East Melbourne, VIC 3002, Australia.
| | - Mirella Dottori
- Centre for Neural Engineering, NICTA, University of Melbourne, 203 Bouverie Street, Parkville, VIC 3010, Australia.
| | - Bryony A Nayagam
- Department of Otolaryngology, University of Melbourne, Royal Victorian Eye and Ear Hospital, Level 2, 32 Gisborne Street, East Melbourne, VIC 3002, Australia; Department of Audiology and Speech Pathology, University of Melbourne, 550 Swanston Street, Parkville, VIC 3010, Australia; Bionics Institute, 384-388 Albert Street, East Melbourne, VIC 3002, Australia.
| |
Collapse
|
16
|
Tang Y, Chen Z, Tao H, Li C, Zhang X, Tang A, Liu Y. Oxytocin activation of neurons in ventral tegmental area and interfascicular nucleus of mouse midbrain. Neuropharmacology 2013; 77:277-84. [PMID: 24148809 DOI: 10.1016/j.neuropharm.2013.10.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2013] [Revised: 10/04/2013] [Accepted: 10/07/2013] [Indexed: 10/26/2022]
Abstract
Oxytocin (OT) was reported to affect cognitive and emotional behavior by action in ventral tegmental area (VTA) and other brain areas. However, it is still unclear how OT activates VTA and related midline nucleus. Here, using patch-clamp recording, we studied the effects of OT on neuron activity in VTA and interfascicular nucleus (IF). OT dose-dependently and selectively excited small neurons located in medial VTA and the majority of IF neurons but not large neurons in lateral VTA. We found the hyperpolarization-activated current (I(h)) and the membrane capacitance of OT-sensitive neuron were significantly smaller than those of OT-insensitive neurons. The action potential width of OT-sensitive neurons was about half that of OT-insensitive neurons. The OT effect was blocked by the OT receptor antagonist atosiban and WAY-267464 but not by tetrodotoxin, suggesting a direct postsynaptic activation of OT receptors. In addition, the phospholipase C (PLC) inhibitor U73122 antagonized the depolarization by OT. Both the nonselective cation channel (NSCC) antagonist SKF96365 and the Na(+)-Ca(2+) exchanger (NCX) blocker SN-6 attenuated OT effects. These results suggested that the PLC signaling pathway coupling to NSCC and NCX contributes to the OT-mediated activation of neurons in medial VTA and IF. Taken together, our results indicate OT directly acted on medial VTA and especially IF neurons to activate NSCC and NCX via PLC. The direct activation by OT of midbrain neurons may be one mechanism underlying OT effects on social behavior.
Collapse
Affiliation(s)
- Yamei Tang
- Department of Laboratory, The Second Xiangya Hospital, Central South University, Changsha 410011, China
| | - Zhiheng Chen
- Department of Pediatrics, The Third Xiangya Hospital, Central South University, Changsha 410013, China
| | - Huai Tao
- Department of Biochemistry and Molecular Biology, Hunan University of Chinese Medicine, Changsha 410208, China
| | - Cunyan Li
- Department of Laboratory, The Second Xiangya Hospital, Central South University, Changsha 410011, China
| | - Xianghui Zhang
- Mental Health Institute, The Second Xiangya Hospital, Central South University, 139 Renmin Middle Road, Changsha 410011, China
| | - Aiguo Tang
- Department of Laboratory, The Second Xiangya Hospital, Central South University, Changsha 410011, China
| | - Yong Liu
- Mental Health Institute, The Second Xiangya Hospital, Central South University, 139 Renmin Middle Road, Changsha 410011, China.
| |
Collapse
|
17
|
Stoenica L, Wilkars W, Battefeld A, Stadler K, Bender R, Strauss U. HCN1 subunits contribute to the kinetics of I(h) in neonatal cortical plate neurons. Dev Neurobiol 2013; 73:785-97. [PMID: 23821600 DOI: 10.1002/dneu.22104] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Revised: 06/13/2013] [Accepted: 06/21/2013] [Indexed: 01/03/2023]
Abstract
The distribution of ion channels in neurons regulates neuronal activity and proper formation of neuronal networks during neuronal development. One of the channels is the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel constituting the molecular substrate of hyperpolarization-activated current (I(h)). Our previous study implied a role for the fastest activating subunit HCN1 in the generation of Ih in rat neonatal cortical plate neurons. To better understand the impact of HCN1 in early neocortical development, we here performed biochemical analysis and whole-cell recordings in neonatal cortical plate and juvenile layer 5 somatosensory neurons of HCN1(-/-) and control HCN1(+/+) mice. Western Blot analysis revealed that HCN1 protein expression in neonatal cortical plate tissue of HCN(+/+) mice amounted to only 3% of the HCN1 in young adult cortex and suggested that in HCN1(-/-) mice other isoforms (particularly HCN4) might be compensatory up-regulated. At the first day after birth, functional ablation of the HCN1 subunit did not affect the proportion of Ih expressing pyramidal cortical plate neurons. Although the contribution of individual subunit proteins remains open, the lack of HCN1 markedly slowed the current activation and deactivation in individual I(h) expressing neurons. However, it did not impair maximal amplitude/density, voltage dependence of activation, and cAMP sensitivity. In conclusion, our data imply that, although expression is relatively low, HCN1 contributes substantially to I(h) properties in individual cortical plate neurons. These properties are significantly changed in HCN1(-/-), either due to the lack of HCN1 itself or due to compensatory mechanisms.
Collapse
Affiliation(s)
- Luminita Stoenica
- Institute of Cell Biology & Neurobiology, Charité-Universitätsmedizin, Berlin, Germany
| | | | | | | | | | | |
Collapse
|
18
|
Yao H, Donnelly DF, Ma C, LaMotte RH. Upregulation of the hyperpolarization-activated cation current after chronic compression of the dorsal root ganglion. J Neurosci 2003; 23:2069-74. [PMID: 12657665 PMCID: PMC6742022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023] Open
Abstract
A chronic compression of the DRG (CCD) produces cutaneous hyperalgesia and an enhanced excitability of neuronal somata in the compressed ganglion. The hyperpolarization-activated current (I(h)), present in the somata and axons of DRG neurons, acts to induce a depolarization after a hyperpolarizing event and, if upregulated after CCD, may contribute to enhanced neuronal excitability. Whole-cell patch-clamp recordings were obtained from acutely dissociated, retrogradely labeled, cutaneous, adult rat DRG neurons of medium size. Neurons were dissociated from L4 and L5 control DRGs or DRGs that had each been compressed for 5-7 d by L-shaped rods inserted into the intervertebral foramina. I(h), consisting of a slowly activating inward current during a step hyperpolarization, was recorded from every labeled, medium-sized neuron and was blocked by 1 mm cesium or 15 microm ZD7288. Compared with control, CCD increased the current density and rate of activation significantly without changing its reversal potential, voltage dependence of activation, or rate of deactivation. Because I(h) activation provides a depolarizing current to the neuron, thus enhancing neuronal excitability, our results are consistent with the hypothesis that I(h) contributes to hyperalgesia after CCD-induced nerve injury.
Collapse
Affiliation(s)
- Hang Yao
- Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | | | | | | |
Collapse
|
19
|
Vasilyev DV, Barish ME. Postnatal development of the hyperpolarization-activated excitatory current Ih in mouse hippocampal pyramidal neurons. J Neurosci 2002; 22:8992-9004. [PMID: 12388606 PMCID: PMC6757670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023] Open
Abstract
The hyperpolarization-activated excitatory current I(h) shapes rhythmic firing and other components of excitability in differentiating neurons, and may thus influence activity-dependent CNS development. We therefore studied developmental changes in I(h) and underlying hyperpolarization-activated cyclic nucleotide-gated (HCN) channel subunits in pyramidal neurons of neonatal mouse hippocampus using electrophysiological and immunofluorescence approaches. I(h) conductance (at -80 mV) tripled in CA3 neurons and quintupled in CA1 neurons between postnatal day 1 (P1) and P20; parallel changes in membrane area resulted in current density maxima at P5 in CA3 and P10 in CA1. Concurrently, I(h) activation times fell sevenfold in CA3 and 10-fold in CA1. A computational model indicates that a decrease in I(h) activation time will increase the rhythmic firing rate. Two mechanisms contributed to more rapid I(h) activation at P20 in CA3 and CA1 neurons: a fall in the intrinsic time constants of two kinetic components, tau(fast) and tau(slow), to 35-40% (at -90 mV) of their P1 values, and a preferential increase in fast component amplitude and contribution to I(h) (from approximately 35% to approximately 74% of total). HCN1, HCN2, and HCN4 immunoreactivities showed independent temporal and spatial developmental patterns. HCN1 immunoreactivity was low at P1 and P5 and increased by P20. HCN2 immunoreactivity was detected at P1 and increased steadily up to P20. HCN4 immunoreactivity was initially low and showed a small increase by P20. We suggest that developmental increases in I(h) amplitude and activation rate reflect changes in the number and underlying structure of I(h) channels, and that I(h) maturation may shape rhythmic activity important for hippocampal circuit maturation.
Collapse
Affiliation(s)
- Dmitry V Vasilyev
- Division of Neurosciences, Beckman Research Institute of the City of Hope, Duarte, California 91010, USA
| | | |
Collapse
|
20
|
Magee JC. Dendritic hyperpolarization-activated currents modify the integrative properties of hippocampal CA1 pyramidal neurons. J Neurosci 1998; 18:7613-24. [PMID: 9742133 PMCID: PMC6793032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Step hyperpolarizations evoked slowly activating, noninactivating, and slowly deactivating inward currents from membrane patches recorded in the cell-attached patch configuration from the soma and apical dendrites of hippocampal CA1 pyramidal neurons. The density of these hyperpolarization-activated currents (Ih) increased over sixfold from soma to distal dendrites. Activation curves demonstrate that a significant fraction of Ih channels is active near rest and that the range is hyperpolarized relatively more in the distal dendrites. Ih activation and deactivation kinetics are voltage-and temperature-dependent, with time constants of activation and deactivation decreasing with hyperpolarization and depolarization, respectively. Ih demonstrated a mixed Na+-K+ conductance and was sensitive to low concentrations of external CsCl. Dual whole-cell recordings revealed regional differences in input resistance (Rin) and membrane polarization rates (taumem) across the somatodendritic axis that are attributable to the spatial gradient of Ih channels. As a result of these membrane effects the propagation of subthreshold voltage transients is directionally specific. The elevated dendritic Ih density decreases EPSP amplitude and duration and reduces the time window over which temporal summation takes place. The backpropagation of action potentials into the dendritic arborization was impacted only slightly by dendritic Ih, with the most consistent effect being a decrease in dendritic action potential duration and an increase in afterhyperpolarization. Overall, Ih acts to dampen dendritic excitability, but its largest impact is on the subthreshold range of membrane potentials where the integration of inhibitory and excitatory synaptic inputs takes place.
Collapse
Affiliation(s)
- J C Magee
- Neuroscience Center, Louisiana State University Medical Center, New Orleans, Louisiana 70112, USA.
| |
Collapse
|