The interaction of the adaptor protein p11, also denoted S100A10, with the C‐terminus of the two‐pore‐domain K+ channel TASK‐1 was studied using yeast two‐hybrid analysis, glutathione S‐transferase pulldown, and co‐immunoprecipitation. We found that p11 interacts with a 40 amino‐acid region in the proximal C‐terminus of the channel. In heterologous expression systems, deletion of the p11‐interacting domain enhanced surface expression of TASK‐1. Attachment of the p11‐interacting domain to the cytosolic tail of the reporter protein CD8 caused retention/retrieval of the construct in the endoplasmic reticulum (ER). Attachment of the last 36 amino acids of p11 to CD8 also caused ER localization, which was abolished by removal or mutation of a putative retention motif (H/K)xKxxx, at the C‐terminal end of p11. Imaging of EGFP‐tagged TASK‐1 channels in COS cells suggested that wild‐type TASK‐1 was largely retained in the ER. Knockdown of p11 with siRNA enhanced trafficking of TASK‐1 to the surface membrane. Our results suggest that binding of p11 to TASK‐1 retards the surface expression of the channel, most likely by virtue of a di‐lysine retention signal at the C‐terminus of p11. Thus, the cytosolic protein p11 may represent a ‘retention factor’ that causes localization of the channel to the ER.

The two-pore-domain potassium channels TASK-1 (KCNK3) and TASK-3 (KCNK9) modulate the electrical activity of neurons and many other cell types. We expressed TASK-1, TASK-3 and related reporter constructs in Xenopus oocytes, mammalian cell lines and various yeast strains to study the mechanisms controlling their transport to the surface membrane and the role of 14-3-3 proteins. We measured potassium currents with the voltage-clamp technique and fused N-and C-terminal fragments of the channels to various reporter proteins to study changes in subcellular localisation and surface expression. Mutational analysis showed that binding of 14-3-3 proteins to the extreme C-terminus of TASK-1 and TASK-3 masks a tri-basic motif, KRR, which differs in several important aspects from canonical arginine-based (RxR) or lysine-based (KKxx) retention signals. Pulldown experiments with GST fusion proteins showed that the KRR motif in the C-terminus of TASK-3 channels was able to bind to COPI coatomer. Disabling the binding of 14-3-3, which exposes the KRR motif, caused localisation of the GFP-tagged channel protein mainly to the Golgi complex. TASK-1 and TASK-3 also possess a di-basic N-terminal retention signal, KR, whose function was found to be independent of the binding of 14-3-3. Suppression of channel surface expression with dominant-negative channel mutants revealed that interaction with 14-3-3 has no significant effect on the dimeric assembly of the channels. Our results give a comprehensive description of the mechanisms by which 14-3-3 proteins, together with N-and C-terminal sorting signals, control the intracellular traffic of TASK-1 and TASK-3.

Background/Aims: Atrial fibrillation is the most common arrhythmia in the elderly, and potassium channels with atrium-specific expression have been discussed as targets to treat atrial fibrillation. Our aim was to characterize TASK-1 channels in human heart and to functionally describe the role of the atrial whole cell current I_TASK-1. Methods and Results: Using quantitative PCR, we show that TASK-1 is predominantly expressed in the atria, auricles and atrio-ventricular node of the human heart. Single channel recordings show the functional expression of TASK-1 in right human auricles. In addition, we describe for the first time the whole cell current carried by TASK-1 channels (I_TASK-1) in human atrial tissue. We show that I_TASK-1 contributes to the sustained outward current I_Ksus and that I_TASK-1 is a major component of the background conductance in human atrial cardiomyocytes. Using patch clamp recordings and mathematical modeling of action potentials, we demonstrate that modulation of I_TASK-1 can alter human atrial action potential duration. Conclusion: Due to the lack of ventricular expression and the ability to alter human atrial action potential duration, TASK-1 might be a drug target for the treatment of atrial fibrillation.

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Our results suggest that the two TREK-like channels found in rat cardiomyocytes may reflect two different operating modes of TREK-1. The novel low-conductance channels described here may represent the major operating mode of TREK-1. The current flowing through mechanogated TREK-1 channels may serve to counterbalance the inward current flowing through stretch-activated non-selective cation channels during the filling phase of the cardiac cycle and thus to prevent the occurrence of ventricular extrasystoles.