Alzheimer's disease (AD) is the commonest neurodegenerative disease that causes memory decline, cognitive dysfunction and behavior disorders in the aged people. Primary pathological hallmarks of AD include amyloid-β (Aβ), neurofibrillary tangles (NFTs), gliosis, and neuronal loss. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels have important physiological functions, especially in aspects of controlling the resting membrane potential, pacemaker activity, memory formation, sleep and arousal. This article reviews the structure, distribution, regulation of HCN channels and the role of HCN channels in the pathological mechanisms of AD, aiming to provide drug therapeutic targets for the prevention and treatment of AD.
Humans ; Alzheimer Disease/physiopathology* ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/physiology* ; Animals ; Amyloid beta-Peptides/metabolism*

Spinal α-motoneurons directly innervate skeletal muscles and function as the final common path for movement and behavior. The processes that determine the excitability of motoneurons are critical for the execution of motor behavior. In fact, it has been noted that spinal motoneurons receive various neuromodulatory inputs, especially monoaminergic one. However, the roles of histamine and hypothalamic histaminergic innervation on spinal motoneurons and the underlying ionic mechanisms are still largely unknown. In the present study, by using the method of intracellular recording on rat spinal slices, we found that activation of either H or H receptor potentiated repetitive firing behavior and increased the excitability of spinal α-motoneurons. Both of blockage of K channels and activation of Na-Ca exchangers were involved in the H receptor-mediated excitation on spinal motoneurons, whereas the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels were responsible for the H receptor-mediated excitation. The results suggest that, through switching functional status of ion channels and exchangers coupled to histamine receptors, histamine effectively biases the excitability of the spinal α-motoneurons. In this way, the hypothalamospinal histaminergic innervation may directly modulate final motor outputs and actively regulate spinal motor reflexes and motor execution.
Animals ; Histamine ; pharmacology ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; metabolism ; Motor Neurons ; drug effects ; physiology ; Rats ; Receptors, Histamine H2 ; metabolism ; Sodium-Calcium Exchanger ; metabolism

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in vertebrate are reverse voltage-dependent, and its activation depends on the hyperpolarization of cell and may be directly or indirectly regulated by the cyclic adenosine monophosphate (cAMP) or other signal transduction cascades. The distribution, quantity, and activation states of HCN channels differ in tissues throughout the body. By modulating If/If current, HCN channels may influence the resting membrane potential, and thus importantly regulate neuronal excitability, dendritic integration of synaptic potentials, and synaptic transmission. Evidence exhibits that HCN channels participate in pain and other physiological and pathological process. Pharmacological treatment targeting HCN channels is of benefit to relieve pain and other related diseases.
Humans ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; physiology ; Membrane Potentials ; Pain ; physiopathology ; Potassium Channels ; Synaptic Transmission

Hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels, distributing in a variety of tissues, especially in excitable cells such as heart cells and many kinds of neurons, have an important role in the modulation of heart rate and neuronal excitability. Different from typical voltage-gated sodium channels and potassium channels, HCN channels were evoked inward currents when the cell was hyperpolarized. More and more recent studies have disclosed that HCN channels play important roles in the nervous system, which were linked with its special electrophysiological features as well as its regulatory effect on the cellular membrane excitability. HCN channels could be modulated by many factors including both extracellular molecules and intracellular signaling cascades, which made its functions complicated in the different condition. Based on its role, HCN channels are presumed to be a promising target for chronic pain and brain disorders. In this paper, we will focus on the advancement of roles of HCN channels in the neural system as well as its complex modulator factors.
Cyclic Nucleotide-Gated Cation Channels ; physiology ; Humans ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; physiology ; Membrane Potentials ; Neurons ; physiology ; Potassium Channels ; physiology

The study was aimed to assess the effect of Klotho gene and sinoatrial node pacing channel gene (HCN4 and HCN2) for studying sick sinus syndrome, with Klotho gene under the interference of Plasmid-mediated short hairpin RNA. Twenty-five C57BL/6J mice were divided into four groups, i. e, plasmid shRNA 24h group, plasmid shRNA 12h group, sodium chloride 24h group and sodium chloride 12h group. Plasmid shRNA 50microL (1microg/microL) and sodium chloride 50microl were respectively injected according to mice vena caudalis into those in plasmid shRNA group and sodium chloride group. After 12h or 24h respectively, all mice were executed and their sinoatrial node tissues were cut. The mRNA of Klotho, HCN4 and HCN2 gene were detected by RT-PCR. The results of RT-PCR showed that Klotho, HCN4 and HCN2 mRNA levels were lower compared with those in sodium chloride 12h group after 12h interference interval. The results indicated that there might be the a certain relationship between Klotho gene and sinoatrial node pacing channel gene.
Animals ; Glucuronidase ; genetics ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; genetics ; metabolism ; Male ; Mice ; Mice, Inbred C57BL ; Plasmids ; genetics ; Potassium Channels ; genetics ; metabolism ; RNA Interference ; RNA, Messenger ; genetics ; metabolism ; RNA, Small Interfering ; genetics ; Sinoatrial Node ; metabolism ; physiology ; physiopathology

To investigate the effects of novel intravenous general anesthetic propofol on membrane electrophysiological characteristics and action potential (AP) of the supraoptic nucleus (SON) neurons and possible ionic mechanisms, intracellular recordings were conducted in SON neurons from the coronal hypothalamic slice preparation of adult male Sprague Dawley (SD) rats. The results showed that bath application of 0.1 mmol/L propofol induced a significant decline in resting potential (P < 0.01), and higher concentrations of propofol (0.3 and 1.0 mmol/L) decreased time constant and slope resistance of cell membrane (P < 0.01). Under the hyperpolarizing current pulses exceeding 0.5 nA, an anomalous rectification was induced by hyperpolarization-activated cation channel (I(h) channel) in 11 out of 18 tested SON neurons. Bath of propofol reversibly decreased the anomalous rectification. Moreover, 0.1 mmol/L propofol elevated threshold level (P < 0.01) and decreased Max L. slope (P < 0.05) of the spike potential in SON neurons. Interestingly, 0.3 and 1.0 mmol/L propofol nullified APs in 6% (1/18) and 71% (12/17) tested SON neurons, respectively. In the SON neurons where APs were not nullified, propofol (0.3 mmol/L) decreased the amplitude of spike potential (P < 0.05). The higher concentrations of propofol (0.3 and 1.0 mmol/L) decreased firing frequencies evoked by depolarizing current pulses (0.1-0.7 nA), and shifted the current intensity-firing frequency relation curves downward and to the right. These results suggest that propofol decreases the excitability of SON neurons by inhibiting I(h) and sodium channels.
Action Potentials ; drug effects ; Anesthetics, Intravenous ; pharmacology ; Animals ; Cyclic Nucleotide-Gated Cation Channels ; antagonists & inhibitors ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; Hypothalamus ; drug effects ; physiology ; In Vitro Techniques ; Male ; Potassium Channels ; Propofol ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Sodium Channel Blockers ; pharmacology ; Supraoptic Nucleus ; drug effects ; physiology

The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels modulate and regulate cardiac rhythm and rate. It has been suggested that, unlike the HCN1 and HCN2 channels, the slower HCN4 channel may not exhibit voltage-dependent hysteresis. We studied the electrophysiological properties of human HCN4 (hHCN4) channels and its modulation by cAMP to determine whether hHCN4 exhibits hysteresis, by using single-cell patch-clamp in HEK293 cells stably transfected with hHCN4. Quantitative real-time RT-PCR was also used to determine levels of expression of HCNs in human cardiac tissue. Voltage-clamp analysis revealed that hHCN4 current (I(h)) activation shifted in the depolarizing direction with more hyperpolarized holding potentials. Triangular ramp and action potential clamp protocols also revealed hHCN4 hysteresis. cAMP enhanced I(h) and shifted activation in the depolarizing direction, thus modifying the intrinsic hHCN4 hysteresis behavior. Quantitative PCR analysis of human sinoatrial node (SAN) tissue showed that HCN4 accounts for 75% of the HCNs in human SAN while HCN1 (21%), HCN2 (3%), and HCN3 (0.7%) constitute the remainder. Our data suggest that HCN4 is the predominant HCN subtype in the human SAN and that I(h) exhibits voltage-dependent hysteresis behavior that can be modified by cAMP. Therefore, hHCN4 hysteresis potentially plays a crucial role in human SAN pacemaking activity.
Biological Clocks ; physiology ; Cyclic AMP ; physiology ; Cyclic Nucleotide-Gated Cation Channels ; physiology ; Electrophysiological Phenomena ; HEK293 Cells ; Humans ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; Muscle Proteins ; physiology ; Patch-Clamp Techniques ; Potassium Channels ; Sinoatrial Node ; physiology ; Transfection

BACKGROUNDExtensive research toward creating a biological pacemaker by enhancement of inward depolarizing current has been performed. However, studies have mainly focused on inducing spontaneous activity and have not adequately addressed ways to improve pacemaker function. In this study we attempted to improve pacemaker function by altering connexin expression in rat mesenchymal stem cells (MSCs) to a phenotype similar to native sinus node pacemaker cells.

METHODSTo generate a biological pacemaker, MSCs were transduced with a cardiac pacemaker gene-hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4), via transfection with a lentiviral vector. Funny current (I(f)) in HCN4(+) MSCs was recorded by voltage-clamp. Overexpression of connexin 45 (gene Gja7) in MSCs was achieved by transfection with the plasmid pDsRED2-N1-Gja7-RFP. Double-immunolabelling with anti-connexin 43 and anti-connexin 45 antibodies were used to identify the gap junction channels. The effects of the genetically modified MSCs on cardiomyocyte excitability were determined in MSCs cocultured with neonatal rat ventricular myocytes. Spontaneous action potentials of neonatal rat ventricular myocytes were recorded by current-clamp.

RESULTSHigh level time- and voltage-dependent inward hyperpolarization current that was sensitive to 4 mmol/L Cs(+) was detected in HCN4(+) MSCs, confirming that HCN4 acted as I(f) channels in MSCs. Connexin 43 and connexin 45 were simultaneously detected in CX45(+) MSCs. Beating frequency was (82 +/- 8) beats per minute (n = 5) in myocytes cocultured with non-transfected control MSCs, versus (129 +/- 11) beats per minute (n = 5) in myocytes cocultured with HCN4(+) MSCs. Myocytes cocultured with MSCs cotransfected with HCN4 and connexin 45 had the highest beating frequency at (147 +/- 9) beats per minute (n = 5).

CONCLUSIONThese findings demonstrate that overexpression of connexin 45 and subsequent formation of heteromeric connexin 45/connexin 43 gap junction channels in HCN4 expressing MSCs can improve their function as cardiac biological pacemakers in vitro.

Animals ; Animals, Newborn ; Biological Clocks ; physiology ; Cells, Cultured ; Connexins ; genetics ; metabolism ; Electrophysiology ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; Mesenchymal Stromal Cells ; cytology ; metabolism ; physiology ; Myocytes, Cardiac ; cytology ; metabolism ; physiology ; Potassium Channels ; genetics ; metabolism ; Rats ; Rats, Sprague-Dawley ; Reverse Transcriptase Polymerase Chain Reaction

AIMTo record funny currents (If) of ventricular myocytes and to analysize hyperpolarization-activated cation channel(HCN) expression in the rats of different ages.

METHODSFresh ventricular myocytes were isolated from 3 days rats and adult rats.HCN expressions were measured by real-time quantitative polymerase chain reaction(real-time PCR). It was recorded through whole-cell patch clamp.

RESULTSHCN1, HCN2, HCN3, HCN4 mRNA represented 0.23% +/- 0.01%, 83.58% +/- 0.04%, 0.79% +/- 0.01%, 15.44% +/- 0.01% of total HCN mRNA in the neonatal rats, respectively. If was recorded and the threshold for activation was -75 mV. In the adult rat, HCN1, HCN2, HCN3, HCN4 mRNA represented 0.72% +/- 0.02%, 91.58% +/- 0.08%, 0.27% +/- 0.02%, 7.12% +/- 0.02% of total HCN mRNA. The ratio of HCN2 to HCN4 was approximately (13.06 +/- 0.21):1. The threshold for activation of If was approximately -115 mV in the adult rats.

CONCLUSIONWith the development of rats, the value of If is smaller. The threshold for activation of If is more negative. The ratio of HCN2 to HCN4 is bigger.

Age Factors ; Animals ; Animals, Newborn ; Cells, Cultured ; Cyclic Nucleotide-Gated Cation Channels ; metabolism ; physiology ; Heart Ventricles ; cytology ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; Ion Channels ; metabolism ; Myocytes, Cardiac ; cytology ; physiology ; Patch-Clamp Techniques ; Potassium Channels ; metabolism ; physiology ; RNA, Messenger ; metabolism ; Rats ; Rats, Sprague-Dawley

Cell Line ; Cyclic Nucleotide-Gated Cation Channels ; physiology ; Humans ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; Ion Channels ; physiology ; Membrane Potentials ; Muscle Proteins ; physiology ; Potassium Channels