G019 Cholesterol depletion enhances Kv1.5-encoded K+ current by increasing Rab11-mediated recycling

Membrane lipid composition is a major determinant of protein organisation in the cell membrane. In a previous study, we reported that depletion of membrane cholesterol by methyl-fÒ-cyclodextrin (MCD) causes a marked increase in Kv1.5-current (Ikur) in neonatal cardiac myocytes. Here, we examined the mechanisms of the cholesterol effects on potassium current in adult rat cardiomyocytes (ARC). GFP-tagged Kv1.5 channels were transduced in ARC using adenoviral vectors and patch clamp experiments were performed to record whole-cell currents and single channel activity. Fluorescence recovery after photobleaching (FRAP) technique was used to investigate GFP-Kv1.5 channels mobility; 3D-epifluorescence microscopy was conducted to follow Kv1.5 channels trafficking.In both freshly isolated and cultured ARC over-expressing GFP-Kv1.5 channels, MCD induced a rapid (< 7min) increase in Ikur but not Ito. On the contrary, incubation with the cholesterol donor LDL reduced Ikur. Single channel experiments revealed that MCD application caused a progressive and drastic increase of the number of active channels. Moreover, FRAP experiments showed that MCD reduced both mobility and recovery of GFP-Kv1.5. Several steps of the trafficking process of ion channels were studied. Blocking SNARE-mediated exocytosis with N-ethylmaleimide prevented the MCD-effect on Ikur. While disruption of Golgi complex/secretion pathway with brefeldine-A had no effect, manipulation of GTP-ases activity with GTP-f×-S suppressed the MCD effect. Transfection with a dominant negative (DN) form of Rab11 effect but not Rab4 DN prevented the MCD. Moreover, Kv1.5 channels co-immunoprecipitated with Rab11 which is stringly expressed in myocardium and ARC (qPCR and western blot). Finally, 3D-microscopy evidenced that Kv1.5 channels association with Rab11-positive recycling endosomes observed in control condition disappeared following cholesterol depletion.ConclusionLowering cholesterol rapidly induces the insertion of Kv1.5 channels by a process that involves vesicle fusion and trafficking processes, particularly the Rab11-associated slow recycling pathway. Given the role of Kv1.5 channel in normal and pathological atrial electrical properties, this study opens news perspectives for therapeutic modulation of cardiac myocytes excitability

A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors

Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that underlies lateral inhibition and establishes the antagonistic center-surround organization of the visual system. Cones transmit to HCs through an excitatory synapse and HCs feed back to cones through an inhibitory synapse. Here we report that HCs also transmit to cone terminals a positive feedback signal that elevates intracellular Ca2+ and accelerates neurotransmitter release. Positive and negative feedback are both initiated by AMPA receptors on HCs, but positive feedback appears to be mediated by a change in HC Ca2+, whereas negative feedback is mediated by a change in HC membrane potential. Local uncaging of AMPA receptor agonists suggests that positive feedback is spatially constrained to active HC-cone synapses, whereas the negative feedback signal spreads through HCs to affect release from surrounding cones. By locally offsetting the effects of negative feedback, positive feedback may amplify photoreceptor synaptic release without sacrificing HC-mediated contrast enhancement

Ion Channel Trafficking: Control of Ion Channel Density as a Target for Arrhythmias?

The shape of the cardiac action potential (AP) is determined by the contributions of numerous ion channels. Any dysfunction in the proper function or expression of these ion channels can result in a change in effective refractory period (ERP) and lead to arrhythmia. The processes underlying the correct targeting of ion channels to the plasma membrane are complex, and have not been fully characterized in cardiac myocytes. Emerging evidence highlights ion channel trafficking as a potential causative factor in certain acquired and inherited arrhythmias, and therapies which target trafficking as opposed to pore block are starting to receive attention. In this review we present the current evidence for the mechanisms which underlie precise control of cardiac ion channel trafficking and targeting

An inventory of major European bird collections

number of staff members of European ornithological collections expressed the opinion that more cooperation among them was desirable. Many museums suffer fro

Human epicardial adipose tissue induces fibrosis of the atrial myocardium through the secretion of adipo-fibrokines

Recent studies have reported a relationship between the abundance of epicardial adipose tissue (EAT) and the risk of cardiovascular diseases including atrial fibrillation (AF). However, the underlying mechanisms are unknown. The aim of this study was to examine the effects of the secretome of human EAT on the histological properties of the myocardium