Cyclic nucleotide-regulated cation channels are ion channels whose activation is regulated by the direct binding of cAMP or cGMP to the channel protein. Two structurally related families of channels ...regulated by cyclic nucleotides have been identified, the cyclic nucleotide-gated channels and the hyperpolarization-activated cyclic nucleotide-gated channels. Cyclic nucleotide-gated channels play a key role in visual and olfactory transduction. Hyperpolarization-activated cyclic nucleotide-gated channels are present in the conduction system of the heart and are involved in the control of cardiac automaticity. Moreover, these channels are widely expressed in central and peripheral neurons, where they control a variety of fundamental processes.
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have a key role in the control of heart rate and neuronal excitability. Ivabradine is the first compound acting on HCN channels to ...be clinically approved for the treatment of angina pectoris. HCN channels may offer excellent opportunities for the development of novel anticonvulsant, anaesthetic and analgesic drugs. In support of this idea, some well-established drugs that act on the central nervous system - including lamotrigine, gabapentin and propofol - have been found to modulate HCN channel function. This Review gives an up-to-date summary of compounds acting on HCN channels, and discusses strategies to further explore the potential of these channels for therapeutic intervention.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Center for Integrated Protein Science CIPS-M and Zentrum für Pharmaforschung, Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Munich, Germany
...Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels comprise a small subfamily of proteins within the superfamily of pore-loop cation channels. In mammals, the HCN channel family comprises four members (HCN1-4) that are expressed in heart and nervous system. The current produced by HCN channels has been known as I h (or I f or I q ). I h has also been designated as pacemaker current, because it plays a key role in controlling rhythmic activity of cardiac pacemaker cells and spontaneously firing neurons. Extensive studies over the last decade have provided convincing evidence that I h is also involved in a number of basic physiological processes that are not directly associated with rhythmicity. Examples for these non-pacemaking functions of I h are the determination of the resting membrane potential, dendritic integration, synaptic transmission, and learning. In this review we summarize recent insights into the structure, function, and cellular regulation of HCN channels. We also discuss in detail the different aspects of HCN channel physiology in the heart and nervous system. To this end, evidence on the role of individual HCN channel types arising from the analysis of HCN knockout mouse models is discussed. Finally, we provide an overview of the impact of HCN channels on the pathogenesis of several diseases and discuss recent attempts to establish HCN channels as drug targets.
5-Hydroxymethylcytosine (hmC) was recently detected as the sixth base in mammalian tissue at so far controversial levels. The function of the modified base is currently unknown, but it is certain ...that the base is generated from 5-methylcytosine (mC). This fuels the hypothesis that it represents an intermediate of an active demethylation process, which could involve further oxidation of the hydroxymethyl group to a formyl or carboxyl group followed by either deformylation or decarboxylation. Here, we use an ultra-sensitive and accurate isotope based LC-MS method to precisely determine the levels of hmC in various mouse tissues and we searched for 5-formylcytosine (fC), 5-carboxylcytosine (caC), and 5-hydroxymethyluracil (hmU) as putative active demethylation intermediates. Our data suggest that an active oxidative mC demethylation pathway is unlikely to occur. Additionally, we show using HPLC-MS analysis and immunohistochemistry that hmC is present in all tissues and cell types with highest concentrations in neuronal cells of the CNS.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The first step in vision is the absorption of photons by the photopigments in cone and rod photoreceptors. After initial amplification within the phototransduction cascade the signal is translated ...into an electrical signal by the action of cyclic nucleotide-gated (CNG) channels. CNG channels are ligand-gated ion channels that are activated by the binding of cyclic guanosine monophosphate (cGMP) or cyclic adenosine monophosphate (cAMP). Retinal CNG channels transduce changes in intracellular concentrations of cGMP into changes of the membrane potential and the Ca
concentration. Structurally, the CNG channels belong to the superfamily of pore-loop cation channels and share a common gross structure with hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and voltage-gated potassium channels (KCN). In this review, we provide an overview on the molecular properties of CNG channels and describe their physiological role in the phototransduction pathways. We also discuss insights into the pathophysiological role of CNG channel proteins that have emerged from the analysis of CNG channel-deficient animal models and human CNG channelopathies. Finally, we summarize recent gene therapy activities and provide an outlook for future clinical application.
Ebola virus causes sporadic outbreaks of lethal hemorrhagic fever in humans, but there is no currently approved therapy. Cells take up Ebola virus by macropinocytosis, followed by trafficking through ...endosomal vesicles. However, few factors controlling endosomal virus movement are known. Here we find that Ebola virus entry into host cells requires the endosomal calcium channels called two-pore channels (TPCs). Disrupting TPC function by gene knockout, small interfering RNAs, or small-molecule inhibitors halted virus trafficking and prevented infection. Tetrandrine, the most potent small molecule that we tested, inhibited infection of human macrophages, the primary target of Ebola virus in vivo, and also showed therapeutic efficacy in mice. Therefore, TPC proteins play a key role in Ebola virus infection and may be effective targets for antiviral therapy.
Hyperpolarization-activated cyclic nucleotide–gated (HCN) channels are the molecular correlate of the I
f
current and are critically involved in controlling neuronal excitability and the autonomous ...rhythm of the heart. The HCN4 isoform is the main HCN channel subtype expressed in the sinoatrial node (SAN), a tissue composed of specialized pacemaker cells responsible for generating the intrinsic heartbeat. More than 40 years ago, the I
f
current was first discovered in rabbit SAN tissue. Along with this discovery, a theory was proposed that cyclic adenosine monophosphate–dependent modulation of I
f
mediates heart rate regulation by the autonomic nervous system—a process called chronotropic effect. However, up to the present day, this classical theory could not be reliably validated. Recently, new concepts emerged confirming that HCN4 channels indeed play an important role in heart rate regulation. However, the cellular mechanism by which HCN4 controls heart rate turned out to be completely different than originally postulated. Here, we review the latest findings regarding the physiological role of HCN4 in the SAN. We describe a newly discovered mechanism underlying heart rate regulation by HCN4 at the tissue and single cell levels, and we discuss these observations in the context of results from previously studied HCN4 mouse models.
Key points
HCN ion channels conducting the Ih current control the frequency of firing in peripheral sensory neurons signalling pain.
Previous studies have demonstrated a major role for the HCN2 ...subunit in chronic pain but the potential involvement of HCN3 in pain has not been investigated.
HCN3 was found to be widely expressed in all classes of sensory neurons (small, medium, large) where it contributes to Ih.
HCN3 deletion increased the firing rate of medium but not small, sensory neurons.
Pain sensitivity both acutely and following neuropathic injury was largely unaffected by HCN3 deletion, with the exception of a small decrease of mechanical hyperalgesia in response to a pinprick.
We conclude that HCN3 plays little role in either acute or chronic pain sensation.
HCN ion channels govern the firing rate of action potentials in the pacemaker region of the heart and in pain‐sensitive (nociceptive) nerve fibres. Intracellular cAMP promotes activation of the HCN4 and HCN2 isoforms, whereas HCN1 and HCN3 are relatively insensitive to cAMP. HCN2 modulates action potential firing rate in nociceptive neurons and plays a critical role in all modes of inflammatory and neuropathic pain, although the role of HCN3 in nociceptive excitability and pain is less studied. Using antibody staining, we found that HCN3 is expressed in all classes of somatosensory neurons. In small nociceptive neurons, genetic deletion of HCN2 abolished the voltage shift of the Ih current carried by HCN isoforms following cAMP elevation, whereas the voltage shift was retained following deletion of HCN3, consistent with the sensitivity of HCN2 but not HCN3 to cAMP. Deletion of HCN3 had little effect on the evoked firing frequency in small neurons but enhanced the firing of medium‐sized neurons, showing that HCN3 makes a significant contribution to the input resistance only in medium‐sized neurons. Genetic deletion of HCN3 had no effect on acute thresholds to heat or mechanical stimuli in vivo and did not affect inflammatory pain measured with the formalin test. Nerve‐injured HCN3 knockout mice exhibited similar levels of mechanical allodynia and thermal hyperalgesia to wild‐type mice but reduced mechanical hyperalgesia in response to a pinprick. These results show that HCN3 makes some contribution to excitability, particularly in medium‐sized neurons, although it has no major influence on acute or neuropathic pain processing.
Key points
HCN ion channels conducting the Ih current control the frequency of firing in peripheral sensory neurons signalling pain.
Previous studies have demonstrated a major role for the HCN2 subunit in chronic pain but the potential involvement of HCN3 in pain has not been investigated.
HCN3 was found to be widely expressed in all classes of sensory neurons (small, medium, large) where it contributes to Ih.
HCN3 deletion increased the firing rate of medium but not small, sensory neurons.
Pain sensitivity both acutely and following neuropathic injury was largely unaffected by HCN3 deletion, with the exception of a small decrease of mechanical hyperalgesia in response to a pinprick.
We conclude that HCN3 plays little role in either acute or chronic pain sensation.
Mind over matter: LC‐MS has allowed the amount of the post‐replicatively formed DNA base 5‐hydroxymethylcytosine (see picture; left) to be quantified in brain tissue. The nucleoside is most abundant ...in areas that are associated with higher cognitive functions, and its content in mouse hippocampi seems to increase with age. The new method enables hydroxymethylcytosine to be quantified with unprecedented accuracy.
The cone function is essential to mediate high visual acuity, color vision, and daylight vision. Inherited cone dystrophies and age-related macular degeneration affect a substantial percentage of the ...world population. To identify and isolate the most competent cells for transplantation and integration into the retina, cone tracing during development would be an important added value. To that aim, the Chrnb4-EGFP mouse line was characterized throughout retinogenesis. It revealed a sub-population of early retinal progenitors expressing the reporter gene that is progressively restricted to mature cones during retina development. The presence of the native CHRNB4 protein was confirmed in EGFP-positive cells, and it presents a similar pattern in the human retina. Sub-retinal transplantations of distinct subpopulations of Chrnb4-EGFP-expressing cells revealed the embryonic day 15.5 high-EGFP population the most efficient cells to interact with host retinas to provoke the appearance of EGFP-positive cones in the photoreceptor layer. Importantly, transplantations into the DsRed retinas revealed material exchanges between donor and host retinas, as >80% of transplanted EGFP-positive cones also were DsRed positive. Whether this cell material fusion is of significant therapeutic advantage requires further thorough investigations. The Chrnb4-EGFP mouse line definitely opens new research perspectives in cone genesis and retina repair.
In adult mouse and human retina, the beta-4 subunit of the Acetylcholine receptor (CHRNB4) is expressed only in cones. The Chrnb4-EGFP mouse served for cone lineage-tracing and transplantation studies. Transplantation of Chrnb4-EGFP cone precursors into DsRed retina revealed frequent bidirectional cellular material exchanges between donor and host cones.
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