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hyperpolarization activated cyclic nucleotide-gated potassium channel 2
HCN channels are voltage-gated ionic channels, regulated by cyclic nucleotides, such as cyclic adenosine-mono-phosphate (cAMP). In contrast to most Na+ and K+ ionic channels, which open when membrane potential is depolarized, they are opened when the membrane potential hyperpolarizes below -50 mV. 
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Hcn2 : hyperpolarization activated cyclic nucleotide-gated potassium channel 2
MinK-related peptide 1 encoded by KCNE2
HCN isoforms in the CHO cell system exposed to MinK-related peptide 1 at whole cell level and single cell level:
On the whole-cell level:
Current densities of all HCN isoforms were significantly increased by KCNE2 without altering voltage dependence or current reversal. All HCN subtypes displayed faster activation kinetics upon co-expression with KCNE2.
KCNE2 expression increased amplitudes and conductance of HCN1, HCN2 and HCN4 significantly. Mean open time was significantly increased in cells co-expressing HCN2+KCNE2, while it was unaffected in HCN1+KCNE2 and reduced in HCN4+KCNE2 co-transfected cells compared to the respective HCN subunits alone. 
Lidocaine inhibited HCN1, HCN2, HCN1-HCN2 and HCN4 channel currents at 100 μM in both oocytes and/or HEK293 cells; it caused a decrease in both tonic and maximal current (~30 to 50% inhibition) and slowed current activation kinetics for all subunits. Lidocaine evoked a hyperpolarizing shift in half-activation voltage but only for HCN1 and HCN1-HCN2 channels. 
The transmembrane protein KCR1 reduces HCN2 current densities and affects single- channel current parameters of this channel. 
HCN1 (but not HCN2 or HCN4) binds filamin A, a putative cytoplasmic scaffold protein that binds actin. It causes clustering and slows down activation and deactivation kinetics of HCN1. 
Disruption of lipid rafts by cholesterol depletion caused a redistribution of HCN channels and thus influenced their kinetics.
CARTOON REPRESENTATION OF HCN2
Cartoon of the HCN2 channel illustrating epilepsy associated amino acid variation, proposed TRIP8b binding sites and predicted proteolytic truncation in the C-terminus of the cardiac channel 
A model of the pore of HCN channels, based on the following assumptions, matched well with experiments: In the closed state, the topology of the inner pore of HCN channels is similar to that of K1 channels. In particular, the orientation of the S5 and S6 helices of HCN channels is very similar to that of the corresponding helices of the K1 KcsA and K1 KirBac1.1 channels. In the open state, the S6 helix is bent further than it is in the closed state. 
Expression of HCN2 in CNS
HCN2 is distributed nearly ubiquitously, with the highest expression in the thalamus, brainstem nuclei and small nociceptive DRG neurons 
The hyperpolarization-activated cation current If/Ih - and thus associated HCN channels - has been identified in various regions of the mammalian heart, the brain, the peripheral nervous system and the eye. 
In the murine sinoatrial node, HCN4 is the most prominently expressed HCN channel, 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 dorsal root ganglion neurons, the dominant HCN transcript is HCN1, followed by HCN2. 
HCN2 is distributed nearly ubiquitously throughout most brain regions, with the highest expression in the thalamus and brain stem nuclei. 
HCN channel activity can modulate the GABAergic synaptic transmission in the basolateral amygdala, which in turn control the amygdala-related emotional behaviors such as anxiety.
The role of HCN channels in the following processes has been studied: dendritic integration, working memory, constraining hippocampal LTP, motor learning , synaptic transmission, resonance and oscillations, the generation of thalamic rhythms, generation of cardiac rythmicity. 
All four HCN channels, HCN1-4, measured in transfected HEK293 cells, exhibit very similar half maximal activation potentials. In contrast, the channels displayed considerable differences in their activation rates in the order HCN1 > HCN2 > HCN3 > HCN4. [2
 HCN2 (Model ID = 10)
Editor : Admin.
Contributors : Rajnish Ranjan, Michael Schartner, Nitin Khanna
To cite : [Editor], [Contributors]. Accessed on [Date] Channelpedia , http://channelpedia.epfl.ch/ionchannels/62