Trafficking and Surface Expression of Hyperpolarization-activated Cyclic Nucleotide-gated Channels in Hippocampal Neurons

Abstract

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels mediate the hyperpolarization-activated current I h and thus play important roles in the regulation of brain excitability. The subcellular distribution pattern of the HCN channels influences the effects that they exert on the properties and activity of neurons. However, little is known about the mechanisms that control HCN channel trafficking to subcellular compartments or that regulate their surface expression. Here we studied the dynamics of HCN channel trafficking in hippocampal neurons using dissociated cultures coupled with time lapse imaging of fluorophore-fused HCN channels. HCN1-green fluorescence protein (HCN1-GFP) channels resided in vesicle-like organelles that moved in distinct patterns along neuronal dendrites, and these properties were isoform-specific. HCN1 trafficking required intact actin and tubulin and was rapidly inhibited by activation of either NMDA or AMPA-type ionotropic glutamate receptors in a calcium-dependent manner. Glutamate-induced inhibition of the movement of HCN1-GFP-expressing puncta was associated with increased surface expression of both native and transfected HCN1 channels, and this surface expression was accompanied by augmented I h . Taken together, the results reveal the highly dynamic nature of HCN1 channel trafficking in hippocampal neurons and provide a novel potential mechanism for rapid regulation of I h , and hence of neuronal properties, via alterations of HCN1 trafficking and surface expression.The ion channel repertoire of neurons contributes critically to the regulation of neuronal activity. The response of a neuron to an incoming input depends (among other factors) on the molecular composition of its ion channels, their relative abundance, their subcellular location, and the fine tuning of their biophysical properties (1, 2). Mechanisms that control the function, expression levels, and/or subcellular localization of ion channels can influence neuronal function in many ways and at different time scales (1, 2). During the past decade, dynamic regulations of ion channel trafficking and surface expression have emerged as pivotal mechanisms in many forms of neuronal plasticity. However, whereas substantial advances have been made in uncovering the cellular dynamics of synaptic ion channel trafficking (3), less is known about the transport of extrasynaptic dendritic channels that contribute to intrinsic excitability.Hyperpolarization-activated cyclic nucleotide-gated (HCN) 2 channels are a family of voltage-gated ion channels that mediate a non-selective cationic current named I h . Unlike other voltage-gated ion channels, members of the HCN family are activated upon hyperpolarization of the cell membrane, and this unusual feature endows them with unique and versatile roles in the regulation of neuronal excitability (4). The subcellular distribution of HCN channels varies in different cell types and brain regions and is important for determining the effects that these channels exert on neuronal excita...

The Acid-sensitive, Anesthetic-activated Potassium Leak Channel, KCNK3, Is Regulated by 14-3-3β-dependent, Protein Kinase C (PKC)-mediated Endocytic Trafficking

“…It is interesting to note that under basal conditions, KNCK3 surface expression in primary CGN cultures was Ͻ6% total KCNK3 protein, which differed markedly from observed surface levels in transfected HEK cells. Nevertheless, these values are consistent with those reported for other channels in both primary cultured neurons (62,63) and acute brain slices (64). Low channel surface density (as a fraction of the total available channel) may reflect large intracellular endocytic pools tightly regulated by neuron-specific mechanisms.…”

Decreased hyperpolarization-activated currents in layer 5 pyramidal neurons enhances excitability in focal cortical dysplasia

“…Increased extracellular glutamate levels have been shown to be present in dysplastic cortex (Campbell and Hablitz 2008). In cultured hippocampal neurons, activation of AMPA and NMDA receptors is capable of acutely augmenting HCN1 surface expression while diminishing channel trafficking (Noam et al 2010). It is currently unclear whether the observed decreases in I h are activity dependent or result from the initial cortical injury.…”

Trafficking and Gating of Hyperpolarization-activated Cyclic Nucleotide-gated Channels Are Regulated by Interaction with Tetratricopeptide Repeat-containing Rab8b-interacting Protein (TRIP8b) and Cyclic AMP at Distinct Sites

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