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HCN Channels (hcn + channel)
Selected AbstractsCellular expression and functional characterization of four hyperpolarization-activated pacemaker channels in cardiac and neuronal tissuesFEBS JOURNAL, Issue 6 2001Sven Moosmang Hyperpolarization-activated cation currents (Ih) have been identified in cardiac pacemaker cells and a variety of central and peripheral neurons. Four members of a gene family encoding hyperpolarization-activated, cyclic nucleotide-gated cation channels (HCN1,4) have been cloned recently. Native Ih currents recorded from different cell types exhibit distinct activation kinetics. To determine if this diversity of Ih currents may be caused by differential expression of HCN channel isoforms, we investigated the cellular distribution of the transcripts of HCN1,4 in the murine sinoatrial node, retina and dorsal root ganglion (DRG) by in situ hybridization. In the sinoatrial node, the most prominently expressed HCN channel is HCN4, whereas HCN2 and HCN1 are detected there at moderate and low levels, respectively. Retinal photoreceptors express high levels of HCN1, whereas HCN2, 3 and 4 were not found in these cells. In DRG neurons, the dominant HCN transcript is HCN1, followed by HCN2. We next determined the functional properties of recombinant HCN1,4 channels expressed in HEK293 cells. All four channel types gave rise to Ih currents but displayed marked differences in their activation kinetics. Our results suggest that the heterogeneity of native Ih currents is generated, at least in part, by the tissue-specific expression of HCN channel genes. [source] Metabotropic glutamate receptor 1 activity generates persistent, N -methyl- d -aspartate receptor-dependent depression of hippocampal pyramidal cell excitabilityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2009J. P. Clement Abstract Metabotropic glutamate receptors (mGluRs) are involved in many forms of neuronal plasticity. In the hippocampus, they have well-defined roles in long-lasting forms of both synaptic and intrinsic plasticity. Here, we describe a novel form of long-lasting intrinsic plasticity that we call (S)-3,5-dihydroxyphenylglycine (DHPG)-mediated long-term depression of excitability (DHPG-LDE), and which is generated following transient pharmacological activation of group I mGluRs. In extracellular recordings from hippocampal slices, DHPG-LDE was expressed as a long-lasting depression of antidromic compound action potentials (cAPs) in CA1 or CA3 cells following a 4-min exposure to the group I mGluR agonist (S)-DHPG. A similar phenomenon was also seen for orthodromic fibre volleys evoked in CA3 axons. In single-cell recordings from CA1 pyramids, DHPG-LDE was manifest as persistent failures in antidromic action potential generation. DHPG-LDE was blocked by (S)-(+)- a -amino-4-carboxy-2-methylbenzeneacetic acid (LY367385), an antagonist of mGluR1, but not 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP), an mGluR5 inhibitor. Although insensitive to antagonists of ,-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate/kainate and ,-aminobutyric acidA receptors, DHPG-LDE was blocked by antagonists of N -methyl- d -aspartate (NMDA) receptors. Similarly, in single-cell recordings, DHPG-mediated antidromic spike failures were eliminated by NMDA receptor antagonism. Long after (S)-DHPG washout, DHPG-LDE was reversed by mGluR1 antagonism. A 4-min application of (S)-DHPG also produced an NMDA receptor-dependent persistent depolarization of CA1 pyramidal cells. This depolarization was not solely responsible for DHPG-LDE, because a similar level of depolarization elicited by raising extracellular K+ increased the amplitude of the cAP. DHPG-LDE did not involve HCN channels or protein synthesis, but was eliminated by blockers of protein kinase C or tyrosine phosphatases. [source] Regulated expression of HCN channels and cAMP levels shape the properties of the h current in developing rat hippocampusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2006Rainer Surges Abstract The hyperpolarization-activated current (Ih) contributes to intrinsic properties and network responses of neurons. Its biophysical properties depend on the expression profiles of the underlying hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels and the presence of cyclic AMP (cAMP) that potently and differentially modulates Ih conducted by HCN1, HCN2 and/or HCN4. Here, we studied the properties of Ih in hippocampal CA1 pyramidal cells, the developmental evolution of the HCN-subunit isoforms that contribute to this current, and their interplay with age-dependent free cAMP concentrations, using electrophysiological, molecular and biochemical methods. Ih amplitude increased progressively during the first four postnatal weeks, consistent with the observed overall increased expression of HCN channels. Activation kinetics of the current accelerated during this period, consonant with the quantitative reduction of mRNA and protein expression of the slow-kinetics HCN4 isoform and increased levels of HCN1. The sensitivity of Ih to cAMP, and the contribution of the slow component to the overall Ih, decreased with age. These are likely a result of the developmentally regulated transition of the complement of HCN channel isoforms from cAMP sensitive to relatively cAMP insensitive. Thus, although hippocampal cAMP concentrations increased over twofold during the developmental period studied, the coordinated changes in expression of three HCN channel isoforms resulted in reduced effects of this signalling molecule on neuronal h currents. [source] Dependence of Hyperpolarisation-Activated Cyclic Nucleotide-Gated Channel Activity on Basal Cyclic Adenosine Monophosphate Production in Spontaneously Firing GH3 CellsJOURNAL OF NEUROENDOCRINOLOGY, Issue 7 2006K. Kretschmannova Abstract The hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels play a distinct role in the control of membrane excitability in spontaneously active cardiac and neuronal cells. Here, we studied the expression and role of HCN channels in pacemaking activity, Ca2+ signalling, and prolactin secretion in GH3 immortalised pituitary cells. Reverse transcriptase-polymerase chain reaction analysis revealed the presence of mRNA transcripts for HCN2, HCN3 and HCN4 subunits in these cells. A hyperpolarisation of the membrane potential below ,,60 mV elicited a slowly activating voltage-dependent inward current (Ih) in the majority of tested cells, with a half-maximal activation voltage of ,89.9 ± 4.2 mV and with a time constant of 1.4 ± 0.2 s at ,120 mV. The bath application of 1 mM Cs+, a commonly used inorganic blocker of Ih, and 100 µM ZD7288, a specific organic blocker of Ih, inhibited Ih by 90 ± 4.1% and 84.3 ± 1.8%, respectively. Receptor- and nonreceptor-mediated activation of adenylyl and soluble guanylyl cyclase and the addition of a membrane permeable cyclic adenosine monophosphate (cAMP) analogue, 8-Br-cAMP, did not affect Ih. Inhibition of basal adenylyl cyclase activity, but not basal soluble guanylyl cyclase activity, led to a reduction in the peak amplitude and a leftward shift in the activation curve of Ih by 23.7 mV. The inhibition of the current was reversed by stimulation of adenylyl cyclase with forskolin and by the addition of 8-Br-cAMP, but not 8-Br-cGMP. Application of Cs+ had no significant effect on the resting membrane potential or electrical activity, whereas ZD7288 exhibited complex and Ih -independent effects on spontaneous electrical activity, Ca2+ signalling, and prolactin release. These results indicate that HCN channels in GH3 cells are under tonic activation by basal level of cAMP and are not critical for spontaneous firing of action potentials. [source] Determinants of activation kinetics in mammalian hyperpolarization-activated cation channelsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2001Takahiro M. Ishii 1The structural basis for the different activation kinetics of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels was investigated with the whole-cell patch clamp technique by using HCN1, HCN4, chimeric channels and mutants in a mammalian expression system (COS,7). 2The activation time constant of HCN4 was about 40-fold longer than that of HCN1 when compared at ,100 mV. 3In chimeras between HCN1 and HCN4, the region of the S1 transmembrane domain and the exoplasmic S1-S2 linker markedly affected the activation kinetics. The cytoplasmic region between S6 and the cyclic nucleotide-binding domain (CNBD) also significantly affected the activation kinetics. 4The S1 domain and S1-S2 linker of HCN1 differ from those of HCN4 at eight amino acid residues, and each single point mutation of them changed the activation kinetics less than 2-fold. However, the effects of those mutations were additive and the substitution of the whole S1 and S1-S2 region of HCN1 by that of HCN4 resulted in a 10, to 20-fold slowing. 5The results indicate that S1 and S1-S2, and S6-CNBD are the crucial components for the activation gating of HCN channels. [source] Hyperpolarization-activated cyclic nucleotide-modulated ,HCN' channels confer regular and faster rhythmicity to beating mouse embryonic stem cellsTHE JOURNAL OF PHYSIOLOGY, Issue 3 2008Yang Qu The hyperpolarization-activated cation current (If), and the hyperpolarization-activated cyclic nucleotide-modulated ,HCN' subunits that underlie it, are important components of spontaneous activity in the embryonic mouse heart, but whether they contribute to this activity in mouse embryonic stem cell-derived cardiomyocytes has not been investigated. We address this issue in spontaneously beating cells derived from mouse embryonic stem cells (mESCs) over the course of development in culture. If and action potentials were recorded from single beating cells at early, intermediate and late development stages using perforated whole-cell voltage- and current-clamp techniques. Our data show that the proportion of cells expressing If, and the density of If in these cells, increased during development and correlated with action potential frequency and the rate of diastolic depolarization. The If blocker ZD7288 (0.3 ,m) reduced If and the beating rate of embryoid bodies. Taken together, the activation kinetics of If and results from Western blots are consistent with the presence of the HCN2 and HCN3 isoforms. At all stages of development, isoproterenol (isoprenaline) and acetylcholine shifted the voltage dependence of If to more positive and negative voltages, respectively, and they also increased and decreased the beating rate of embryonic cell bodies, respectively. Together, the data suggest that current through HCN2 and HCN3 channels confers regular and faster rhythmicity to mESCs, which mirrors the developing embryonic mouse heart, and contributes to modulation of rhythmicity by autonomic stimulation. [source] | ||||||||||