The multifaceted phenotype of the knockout mouse for the KCNE1 potassium channel gene

Kv Channel Ancillary Subunits: Where Do We Go from Here?

Voltage-gated potassium (Kv) channels each comprise four pore-forming α-subunits that orchestrate essential duties such as voltage sensing and K+ selectivity and conductance. In vivo, however, Kv channels also incorporate regulatory subunits-some Kv channel specific, others more general modifiers of protein folding, trafficking, and function. Understanding all the above is essential for a complete picture of the role of Kv channels in physiology and disease.

Novel cell types and developmental lineages revealed by single-cell RNA-seq analysis of the mouse crista ampullaris

This study provides transcriptomic characterization of the cells of the crista ampullaris, sensory structures at the base of the semicircular canals that are critical for vestibular function. We performed single-cell RNA-seq on ampullae microdissected from E16, E18, P3, and P7 mice. Cluster analysis identified the hair cells, support cells and glia of the crista as well as dark cells and other nonsensory epithelial cells of the ampulla, mesenchymal cells, vascular cells, macrophages, and melanocytes. Cluster-specific expression of genes predicted their spatially restricted domains of gene expression in the crista and ampulla. Analysis of cellular proportions across developmental time showed dynamics in cellular composition. The new cell types revealed by single-cell RNA-seq could be important for understanding crista function and the markers identified in this study will enable the examination of their dynamics during development and disease.

Molecular Mechanism of Autosomal Recessive Long QT-Syndrome 1 without Deafness

KCNQ1 encodes the voltage-gated potassium (Kv) channel KCNQ1, also known as KvLQT1 or Kv7.1. Together with its ß-subunit KCNE1, also denoted as minK, this channel generates the slowly activating cardiac delayed rectifier current I_Ks, which is a key regulator of the heart rate dependent adaptation of the cardiac action potential duration (APD). Loss-of-function mutations in KCNQ1 cause congenital long QT1 (LQT1) syndrome, characterized by a delayed cardiac repolarization and a prolonged QT interval in the surface electrocardiogram. Autosomal dominant loss-of-function mutations in KCNQ1 result in long QT syndrome, called Romano–Ward Syndrome (RWS), while autosomal recessive mutations lead to Jervell and Lange-Nielsen syndrome (JLNS), associated with deafness. Here, we identified a homozygous KCNQ1 mutation, c.1892_1893insC (p.P631fs*20), in a patient with an isolated LQT syndrome (LQTS) without hearing loss. Nevertheless, the inheritance trait is autosomal recessive, with heterozygous family members being asymptomatic. The results of the electrophysiological characterization of the mutant, using voltage-clamp recordings in Xenopus laevis oocytes, are in agreement with an autosomal recessive disorder, since the I_Ks reduction was only observed in homomeric mutants, but not in heteromeric I_Ks channel complexes containing wild-type channel subunits. We found that KCNE1 rescues the KCNQ1 loss-of-function in mutant I_Ks channel complexes when they contain wild-type KCNQ1 subunits, as found in the heterozygous state. Action potential modellings confirmed that the recessive c.1892_1893insC LQT1 mutation only affects the APD of homozygous mutation carriers. Thus, our study provides the molecular mechanism for an atypical autosomal recessive LQT trait that lacks hearing impairment.

Ion Channel Signature in Healthy Pancreas and Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the fourth most common cause of cancer-related deaths in United States and Europe. It is predicted that PDAC will become the second leading cause of cancer-related deaths during the next decades. The development of PDAC is not well understood, however, studies have shown that dysregulated exocrine pancreatic fluid secretion can contribute to pathologies of exocrine pancreas, including PDAC. The major roles of healthy exocrine pancreatic tissue are secretion of enzymes and bicarbonate rich fluid, where ion channels participate to fine-tune these biological processes. It is well known that ion channels located in the plasma membrane regulate multiple cellular functions and are involved in the communication between extracellular events and intracellular signaling pathways and can function as signal transducers themselves. Hereby, they contribute to maintain resting membrane potential, electrical signaling in excitable cells, and ion homeostasis. Despite their contribution to basic cellular processes, ion channels are also involved in the malignant transformation from a normal to a malignant phenotype. Aberrant expression and activity of ion channels have an impact on essentially all hallmarks of cancer defined as; uncontrolled proliferation, evasion of apoptosis, sustained angiogenesis and promotion of invasion and migration. Research indicates that certain ion channels are involved in the aberrant tumor growth and metastatic processes of PDAC. The purpose of this review is to summarize the important expression, localization, and function of ion channels in normal exocrine pancreatic tissue and how they are involved in PDAC progression and development. As ion channels are suggested to be potential targets of treatment they are furthermore suggested to be biomarkers of different cancers. Therefore, we describe the importance of ion channels in PDAC as markers of diagnosis and clinical factors.

The membrane protein KCNQ1 potassium ion channel: Functional diversity and current structural insights

BACKGROUND

Ion channels play crucial roles in cellular biology, physiology, and communication including sensory perception. Voltage-gated potassium (Kv) channels execute their function by sensor activation, pore-coupling, and pore opening leading to K⁺ conductance.

SCOPE OF REVIEW

This review focuses on a voltage-gated K⁺ ion channel KCNQ1 (Kv 7.1). Firstly, discussing its positioning in the human ion chanome, and the role of KCNQ1 in the multitude of cellular processes. Next, we discuss the overall channel architecture and current structural insights on KCNQ1. Finally, the gating mechanism involving members of the KCNE family and its interaction with non-KCNE partners.

MAJOR CONCLUSIONS

KCNQ1 executes its important physiological functions via interacting with KCNE1 and non-KCNE1 proteins/molecules: calmodulin, PIP₂, PKA. Although, KCNQ1 has been studied in great detail, several aspects of the channel structure and function still remain unexplored. This review emphasizes the structural and biophysical studies of KCNQ1, its interaction with KCNE1 and non-KCNE1 proteins and focuses on several seminal findings showing the role of VSD and the pore domain in the channel activation and gating properties.

GENERAL SIGNIFICANCE

KCNQ1 mutations can result in channel defects and lead to several diseases including atrial fibrillation and long QT syndrome. Therefore, a thorough structure-function understanding of this channel complex is essential to understand its role in both normal and disease biology. Moreover, unraveling the molecular mechanisms underlying the regulation of this channel complex will help to find therapeutic strategies for several diseases.

Clinical update on sensorineural hearing loss in Turner syndrome and the X-chromosome

Hearing loss is one of the major medical concerns in girls and women with Turner syndrome (TS) and has a negative effect on well-being and quality of everyday life. Sensorineural hearing loss is the most common type of hearing loss, affecting more than half of adults with TS. Karyotypes with a loss of the short p-arm on the X-chromosome are more prone to ear and hearing problems. The importance of detecting, investigating, and treating hearing loss with hearing aids cannot be emphasized enough. The pathophysiology of the sensorineural hearing loss in TS is not known, but theories regarding estrogen deficiency, the cell cycle delay hypothesis, IGF-1 deficiency and the possible role of the KDM6A gene are discussed. Due to the diversity of symptoms and conditions within the same karyotype, a combination of genetic factors altered by epigenetic and/or hormonal effects is probable. Further research is needed regarding the pathophysiology of ear and hearing problems in TS to develop new treatment methods.

Deletion in mice of X-linked, Brugada syndrome- and atrial fibrillation-associated Kcne5 augments ventricular KV currents and predisposes to ventricular arrhythmia

KCNE5 is an X-linked gene encoding KCNE5, an ancillary subunit to voltage-gated potassium (K_V) channels. Human KCNE5 mutations are associated with atrial fibrillation (AF)- and Brugada syndrome (BrS)-induced cardiac arrhythmias that can arise from increased potassium current in cardiomyocytes. Seeking to establish underlying molecular mechanisms, we created and studied Kcne5 knockout ( Kcne5^-/0) mice. Intracardiac ECG revealed that Kcne5 deletion caused ventricular premature beats, increased susceptibility to induction of polymorphic ventricular tachycardia (60 vs. 24% in Kcne5^+/0 mice), and 10% shorter ventricular refractory period. Kcne5 deletion increased mean ventricular myocyte K_V current density in the apex and also in the subpopulation of septal myocytes that lack fast transient outward current ( I_to,f). The current increases arose from an apex-specific increase in slow transient outward current-1 ( I_Kslow,1) (conducted by K_V1.5) and I_to,f (conducted by K_V4) and an increase in I_Kslow,2 (conducted by K_V2.1) in both apex and septum. Kcne5 protein localized to the intercalated discs in ventricular myocytes, where K_V2.1 was also detected in both Kcne5^-/0 and Kcne5^+/0 mice. In HL-1 cardiac cells and human embryonic kidney cells, KCNE5 and K_V2.1 colocalized at the cell surface, but predominantly in intracellular vesicles, suggesting that Kcne5 deletion increases I_K,slow2 by reducing K_V2.1 intracellular sequestration. The human AF-associated mutation KCNE5-L65F negative shifted the voltage dependence of K_V2.1-KCNE5 channels, increasing their maximum current density >2-fold, whereas BrS-associated KCNE5 mutations produced more subtle negative shifts in K_V2.1 voltage dependence. The findings represent the first reported native role for Kcne5 and the first demonstrated Kcne regulation of K_V2.1 in mouse heart. Increased K_V current is a manifestation of KCNE5 disruption that is most likely common to both mouse and human hearts, providing a plausible mechanistic basis for human KCNE5-linked AF and BrS.-David, J.-P., Lisewski, U., Crump, S. M., Jepps, T. A., Bocksteins, E., Wilck, N., Lossie, J., Roepke, T. K., Schmitt, N., Abbott, G. W. Deletion in mice of X-linked, Brugada syndrome- and atrial fibrillation-associated Kcne5 augments ventricular K_V currents and predisposes to ventricular arrhythmia.

Regulation of human cardiac potassium channels by full-length KCNE3 and KCNE4

Voltage-gated potassium (Kv) channels comprise pore-forming α subunits and a multiplicity of regulatory proteins, including the cardiac-expressed and cardiac arrhythmia-linked transmembrane KCNE subunits. After recently uncovering novel, N-terminally extended (L) KCNE3 and KCNE4 isoforms and detecting their transcripts in human atrium, reported here are their functional effects on human cardiac Kv channel α subunits expressed in Xenopus laevis oocytes. As previously reported for short isoforms KCNE3S and KCNE4S, KCNE3L inhibited hERG; KCNE4L inhibited Kv1.1; neither form regulated the HCN1 pacemaker channel. Unlike KCNE4S, KCNE4L was a potent inhibitor of Kv4.2 and Kv4.3; co-expression of cytosolic β subunit KChIP2, which regulates Kv4 channels in cardiac myocytes, partially relieved Kv4.3 but not Kv4.2 inhibition. Inhibition of Kv4.2 and Kv4.3 by KCNE3L was weaker, and its inhibition of Kv4.2 abolished by KChIP2. KCNE3L and KCNE4L also exhibited subunit-specific effects on Kv4 channel complex inactivation kinetics, voltage dependence and recovery. Further supporting the potential physiological significance of the robust functional effects of KCNE4L on Kv4 channels, KCNE4L protein was detected in human atrium, where it co-localized with Kv4.3. The findings establish functional effects of novel human cardiac-expressed KCNE isoforms and further contribute to our understanding of the potential mechanisms influencing cardiomyocyte repolarization.

Potassium: From Physiology to Clinical Implications

BACKGROUND

Potassium (K(+)) is the major intracellular cation, with 98% of the total pool being located in the cells at a concentration of 140-150 mmol/l, and only 2% in the extracellular fluid, where it ranges between 3.5 and 5 mmol/l. A fine regulation of the intracellular-extracellular gradient is crucial for life, as it is the main determinant of membrane voltage; in fact, acute changes of K(+) plasma levels may have fatal consequences.

SUMMARY

An integrated system including an 'internal' and 'external' control prevents significant fluctuations of plasma levels in conditions of K(+) loading and depletion. The internal control regulates the intra-extracellular shift, a temporary mechanism able to maintain a constant K(+) plasma concentration without changing the total amount of body K(+). The external control is responsible for the excretion of the ingested K(+), and it has the kidney as the major player. The kidney excretes nearly 90% of the daily intake. Along the proximal tubule and the thick ascending limb on Henle's loop, the amount of K(+) reabsorption is quite fixed (about 80-90%); conversely, the distal nephron has the ability to adjust K(+) excretion in accordance with homeostatic needs. The present review analyzes: (1) the main molecular mechanisms mediating K(+) reabsorption and secretion along the nephron; (2) the pathophysiology of the principal K(+) derangements due to renal dysfunction, and (3) the effect of ingested K(+) on blood pressure and renal electrolyte handling.

KEY MESSAGES

Maintaining plasma K(+) levels in a tight range is crucial for life; thus, multiple factors are implicated in K(+) homeostasis, including kidney function. Recent studies have suggested that K(+) plasma levels, in turn, affect renal salt absorption in animal models; this effect may underlie the reduction of blood pressure observed in hypertensive subjects under K(+) supplementation.

The KCNQ1 channel - remarkable flexibility in gating allows for functional versatility

The KCNQ1 channel (also called Kv7.1 or KvLQT1) belongs to the superfamily of voltage-gated K(+) (Kv) channels. KCNQ1 shares several general features with other Kv channels but also displays a fascinating flexibility in terms of the mechanism of channel gating, which allows KCNQ1 to play different physiological roles in different tissues. This flexibility allows KCNQ1 channels to function as voltage-independent channels in epithelial tissues, whereas KCNQ1 function as voltage-activated channels with very slow kinetics in cardiac tissues. This flexibility is in part provided by the association of KCNQ1 with different accessory KCNE β-subunits and different modulators, but also seems like an integral part of KCNQ1 itself. The aim of this review is to describe the main mechanisms underlying KCNQ1 flexibility.

Estrogen-related receptor gamma and hearing function: evidence of a role in humans and mice

Since estrogen is thought to protect pre-menopausal women from age-related hearing loss, we investigated whether variation in estrogen-signalling genes is linked to hearing status in the 1958 British Birth Cohort. This analysis implicated the estrogen-related receptor gamma (ESRRG) gene in determining adult hearing function and was investigated further in a total of 6134 individuals in 3 independent cohorts: (i) the 1958 British Birth Cohort; (ii) a London ARHL case-control cohort; and (iii) a cohort from isolated populations of Italy and Silk Road countries. Evidence of an association between the minor allele of single nucleotide polymorphism (SNP) rs2818964 and hearing status was found in females, but not in males in 2 of these cohorts: p = 0.0058 (London ARHL) and p = 0.0065 (Carlantino, Italy). Furthermore, assessment of hearing in Esrrg knock-out mice revealed a mild 25-dB hearing loss at 5 weeks of age. At 12 weeks, average hearing thresholds in female mice((-/-)) were 15 dB worse than in males((-/-)). Together these data indicate ESRRG plays a role in maintenance of hearing in both humans and mice.

The KCNE Tango - How KCNE1 Interacts with Kv7.1

The classical tango is a dance characterized by a 2/4 or 4/4 rhythm in which the partners dance in a coordinated way, allowing dynamic contact. There is a surprising similarity between the tango and how KCNE β-subunits "dance" to the fast rhythm of the cell with their partners from the Kv channel family. The five KCNE β-subunits interact with several members of the Kv channels, thereby modifying channel gating via the interaction of their single transmembrane-spanning segment, the extracellular amino terminus, and/or the intracellular carboxy terminus with the Kv α-subunit. Best studied is the molecular basis of interactions between KCNE1 and Kv7.1, which, together, supposedly form the native cardiac I(Ks) channel. Here we review the current knowledge about functional and molecular interactions of KCNE1 with Kv7.1 and try to summarize and interpret the tango of the KCNEs.

Ancillary subunits associated with voltage-dependent K+ channels

Since the first discovery of Kvbeta-subunits more than 15 years ago, many more ancillary Kv channel subunits were characterized, for example, KChIPs, KCNEs, and BKbeta-subunits. The ancillary subunits are often integral parts of native Kv channels, which, therefore, are mostly multiprotein complexes composed of voltage-sensing and pore-forming Kvalpha-subunits and of ancillary or beta-subunits. Apparently, Kv channels need the ancillary subunits to fulfill their many different cell physiological roles. This is reflected by the large structural diversity observed with ancillary subunit structures. They range from proteins with transmembrane segments and extracellular domains to purely cytoplasmic proteins. Ancillary subunits modulate Kv channel gating but can also have a great impact on channel assembly, on channel trafficking to and from the cellular surface, and on targeting Kv channels to different cellular compartments. The importance of the role of accessory subunits is further emphasized by the number of mutations that are associated in both humans and animals with diseases like hypertension, epilepsy, arrhythmogenesis, periodic paralysis, and hypothyroidism. Interestingly, several ancillary subunits have in vitro enzymatic activity; for example, Kvbeta-subunits are oxidoreductases, or modulate enzymatic activity, i.e., KChIP3 modulates presenilin activity. Thus different modes of beta-subunit association and of functional impact on Kv channels can be delineated, making it difficult to extract common principles underlying Kvalpha- and beta-subunit interactions. We critically review present knowledge on the physiological role of ancillary Kv channel subunits and their effects on Kv channel properties.

KV7 channelopathies

KV7 voltage-gated potassium channels, encoded by the KCNQ gene family, have caught increasing interest of the scientific community for their important physiological roles, which are emphasized by the fact that four of the five so far identified members are related to different hereditary diseases. Furthermore, these channels prove to be attractive pharmacological targets for treating diseases characterized by membrane hyperexcitability. KV7 channels are expressed in brain, heart, thyroid gland, pancreas, inner ear, muscle, stomach, and intestines. They give rise to functionally important potassium currents, reduction of which results in pathologies such as long QT syndrome, diabetes, neonatal epilepsy, neuromyotonia, or progressive deafness. Here, we summarize some key traits of KV7 channels and review how their molecular deficiencies could explain diverse disease phenotypes. We also assess the therapeutic potential of KV7 channels; in particular, how the activation of KV7 channels by the compounds retigabine and R-L3 may be useful for treatment of epilepsy or cardiac arrhythmia.

KCNE1 and KCNE3 beta-subunits regulate membrane surface expression of Kv12.2 K(+) channels in vitro and form a tripartite complex in vivo

Voltage-gated potassium channels that activate near the neuronal resting membrane potential are important regulators of excitation in the nervous system, but their functional diversity is still not well understood. For instance, Kv12.2 (ELK2, KCNH3) channels are highly expressed in the cerebral cortex and hippocampus, and although they are most likely to contribute to resting potassium conductance, surprisingly little is known about their function or regulation. Here we demonstrate that the auxiliary MinK (KCNE1) and MiRP2 (KCNE3) proteins are important regulators of Kv12.2 channel function. Reduction of endogenous KCNE1 or KCNE3 expression by siRNA silencing, significantly increased macroscopic Kv12.2 currents in Xenopus oocytes by around 4-fold. Interestingly, an almost 9-fold increase in Kv12.2 currents was observed with the dual injection of KCNE1 and KCNE3 siRNA, suggesting an additive effect. Consistent with these findings, over-expression of KCNE1 and/or KCNE3 suppressed Kv12.2 currents. Membrane surface biotinylation assays showed that surface expression of Kv12.2 was significantly increased by KCNE1 and KCNE3 siRNA, whereas total protein expression of Kv12.2 was not affected. KCNE1 and KCNE3 siRNA shifted the voltages for half-maximal activation to more hyperpolarized voltages, indicating that KCNE1 and KCNE3 may also inhibit activation gating of Kv12.2. Native co-immunoprecipitation assays from mouse brain membranes imply that KCNE1 and KCNE3 interact with Kv12.2 simultaneously in vivo, suggesting the existence of novel KCNE1-KCNE3-Kv12.2 channel tripartite complexes. Together these data indicate that KCNE1 and KCNE3 interact directly with Kv12.2 channels to regulate channel membrane trafficking.

Regulation of the Kv2.1 potassium channel by MinK and MiRP1

Kv2.1 is a voltage-gated potassium (Kv) channel alpha-subunit expressed in mammalian heart and brain. MinK-related peptides (MiRPs), encoded by KCNE genes, are single-transmembrane domain ancillary subunits that form complexes with Kv channel alpha-subunits to modify their function. Mutations in human MinK (KCNE1) and MiRP1 (KCNE2) are associated with inherited and acquired forms of long QT syndrome (LQTS). Here, coimmunoprecipitations from rat heart tissue suggested that both MinK and MiRP1 form native cardiac complexes with Kv2.1. In whole-cell voltage-clamp studies of subunits expressed in CHO cells, rat MinK and MiRP1 reduced Kv2.1 current density three- and twofold, respectively; slowed Kv2.1 activation (at +60 mV) two- and threefold, respectively; and slowed Kv2.1 deactivation less than twofold. Human MinK slowed Kv2.1 activation 25%, while human MiRP1 slowed Kv2.1 activation and deactivation twofold. Inherited mutations in human MinK and MiRP1, previously associated with LQTS, were also evaluated. D76N-MinK and S74L-MinK reduced Kv2.1 current density (threefold and 40%, respectively) and slowed deactivation (60% and 80%, respectively). Compared to wild-type human MiRP1-Kv2.1 complexes, channels formed with M54T- or I57T-MiRP1 showed greatly slowed activation (tenfold and fivefold, respectively). The data broaden the potential roles of MinK and MiRP1 in cardiac physiology and support the possibility that inherited mutations in either subunit could contribute to cardiac arrhythmia by multiple mechanisms.

Re-assigning the DFNB33 locus to chromosome 10p11.23-q21.1

Homozygosity mapping is a powerful resource for mapping and identifying loci and genes responsible for autosomal recessive disorders. Nevertheless, it could result in the identification of several homozygous regions unrelated to the disease locus or non-informative regions. Previously, a genome-wide screen in a large consanguineous Jordanian family allowed us to assign the DFNB33 locus to chromosome 9q34.3. Sequencing of 23 candidate genes showed 11 SNPs in a heterozygous state in affected individuals. These results ruled out the candidate region on chromosome 9. Using additional markers, we were able to restrict the disease locus to an approximately 14 cM region at chromosome 10, located between markers D10S193 and D10S1784. A maximum LOD score of 3.99 was obtained with two markers, D10S199 and D10S220. The screening of two candidate genes, CX40.1 and FXYD4, failed to reveal any disease-causing mutations.

Physiology and pathophysiology of potassium channels in gastrointestinal epithelia

Epithelial cells of the gastrointestinal tract are an important barrier between the "milieu interne" and the luminal content of the gut. They perform transport of nutrients, salts, and water, which is essential for the maintenance of body homeostasis. In these epithelia, a variety of K(+) channels are expressed, allowing adaptation to different needs. This review provides an overview of the current literature that has led to a better understanding of the multifaceted function of gastrointestinal K(+) channels, thereby shedding light on pathophysiological implications of impaired channel function. For instance, in gastric mucosa, K(+) channel function is a prerequisite for acid secretion of parietal cells. In epithelial cells of small intestine, K(+) channels provide the driving force for electrogenic transport processes across the plasma membrane, and they are involved in cell volume regulation. Fine tuning of salt and water transport and of K(+) homeostasis occurs in colonic epithelia cells, where K(+) channels are involved in secretory and reabsorptive processes. Furthermore, there is growing evidence for changes in epithelial K(+) channel expression during cell proliferation, differentiation, apoptosis, and, under pathological conditions, carcinogenesis. In the future, integrative approaches using functional and postgenomic/proteomic techniques will help us to gain comprehensive insights into the role of K(+) channels of the gastrointestinal tract.

KCNQ1 and KCNE1 K+ channel components are involved in early left-right patterning in Xenopus laevis embryos

Several ion transporters have been implicated in left-right (LR) patterning. Here, we characterize a new component of the early bioelectrical circuit: the potassium channel KCNQ1 and its accessory subunit KCNE1. Having cloned the native Xenopus versions of both genes, we show that both are asymmetrically localized as maternal proteins during the first few cleavages of frog embryo development in a process dependent on microtubule and actin organization. Molecular loss-of-function using dominant negative constructs demonstrates that both gene products are required for normal LR asymmetry. We propose a model whereby these channels provide an exit path for K(+) ions brought in by the H(+),K(+)-ATPase. This physiological module thus allows the obligate but electroneutral H(+),K(+)-ATPase to generate an asymmetric voltage gradient on the left and right sides. Our data reveal a new, bioelectrical component of the mechanisms patterning a large-scale axis in vertebrate embryogenesis.

No potassium, no acid: K+ channels and gastric acid secretion

The gastric H+-K+-ATPase pumps H+ into the lumen and takes up K+ in parallel. In the acid-producing parietal cells, luminal KCNE2/KCNQ1 K+ channels play a pivotal role in replenishing K+ in the luminal fluid. Inactivation of KCNE2/KCNQ1 channels abrogates gastric acid secretion and dramatically modifies the architecture of gastric mucosa.

Developmental regulation of the membrane properties of central vestibular neurons by sensory vestibular information in the mouse

The effect of the lack of vestibular input on the membrane properties of central vestibular neurons was studied by using a strain of transgenic, vestibular-deficient mutant KCNE1(-/-) mice where the hair cells of the inner ear degenerate just after birth. Despite the absence of sensory vestibular input, their central vestibular pathways are intact. Juvenile and adult homozygous mutant have a normal resting posture, but show a constant head bobbing behaviour and display the shaker/waltzer phenotype characterized by rapid bilateral circling during locomotion. In juvenile mice, the KCNE1 mutation was associated with a strong decrease in the expression of the calcium-binding proteins calbindin, calretinin and parvalbumin within the medial vestibular nucleus (MVN) and important modifications of the membrane properties of MVN neurons. In adult mice, however, there was almost no difference between the membrane properties of MVN neurons of homozygous and control or heterozygous mutant mice, which have normal inner ear hair cells and show no behavioural symptoms. The expression levels of calbindin and calretinin were lower in adult homozygous mutant animals, but the amount of calcium-binding proteins expressed in the MVN was much greater than in juvenile mice. These data demonstrate that suppression of sensory vestibular inputs during a 'sensitive period' around birth can generate the circling/waltzing behaviour, but that this behaviour is not due to persistent abnormalities of the membrane properties of central vestibular neurons. Altogether, maturation of the membrane properties of central vestibular neurons is delayed, but not impaired by the absence of sensory vestibular information.

The role of S4 charges in voltage-dependent and voltage-independent KCNQ1 potassium channel complexes

Voltage-gated potassium (Kv) channels extend their functional repertoire by coassembling with MinK-related peptides (MiRPs). MinK slows the activation of channels formed with KCNQ1 α subunits to generate the voltage-dependent I_Ks channel in human heart; MiRP1 and MiRP2 remove the voltage dependence of KCNQ1 to generate potassium “leak” currents in gastrointestinal epithelia. Other Kv α subunits interact with MiRP1 and MiRP2 but without loss of voltage dependence; the mechanism for this disparity is unknown. Here, sequence alignments revealed that the voltage-sensing S4 domain of KCNQ1 bears lower net charge (+3) than that of any other eukaryotic voltage-gated ion channel. We therefore examined the role of KCNQ1 S4 charges in channel activation using alanine-scanning mutagenesis and two-electrode voltage clamp. Alanine replacement of R231, at the N-terminal side of S4, produced constitutive activation in homomeric KCNQ1 channels, a phenomenon not observed with previous single amino acid substitutions in S4 of other channels. Homomeric KCNQ4 channels were also made constitutively active by mutagenesis to mimic the S4 charge balance of R231A-KCNQ1. Loss of single S4 charges at positions R231 or R237 produced constitutively active MinK-KCNQ1 channels and increased the constitutively active component of MiRP2-KCNQ1 currents. Charge addition to the CO₂H-terminal half of S4 eliminated constitutive activation in MiRP2-KCNQ1 channels, whereas removal of homologous charges from KCNQ4 S4 produced constitutively active MiRP2-KCNQ4 channels. The results demonstrate that the unique S4 charge paucity of KCNQ1 facilitates its unique conversion to a leak channel by ancillary subunits such as MiRP2.

Mechanisms of ventricular arrhythmogenesis in mice following targeted disruption of KCNE1 modelling long QT syndrome 5

Mutations within KCNE1 encoding a transmembrane protein which coassembles with K+ channels mediating slow K+, I(Ks), currents are implicated in cardiac action potential prolongation and ventricular arrhythmogenicity in long QT syndrome 5. We demonstrate the following potentially arrhythmogenic features in simultaneously recorded, left ventricular, endocardial and epicardial monophasic action potentials from Langendorff-perfused murine KCNE1-/- hearts for the first time. (1) Prolonged epicardial (57.1 +/- 0.5 ms cf. 36.1 +/- 0.07 ms in wild-type (WT), P < 0.001; n = 5) and endocardial action potential duration at 90% repolarication (APD90) (54.4 +/- 2.4 ms cf. 48.5 +/- 0.3 ms, P < 0.05; n = 5). (2) Negative transmural repolarization gradients (DeltaAPD90: endocardial minus epicardial APD90) (-2.5 +/- 2.4 ms, compared with 12.4 +/- 1.1 ms in WT, P < 0.001; n = 5). (3) Frequent epicardial early afterdepolarizations (EADs) and spontaneous ventricular tachycardia (VT) in 4 out of 5 KCNE1-/- hearts but not WT (n = 5). EADs were especially frequent following temporary cessations of ventricular pacing. (4) Monomorphic VT lasting 1.36 +/- 0.2 s in 5 out of 5 KCNE1-/- hearts, following premature stimuli but not WT (n = 5). (5) Epicardial APD alternans. Perfusion of KCNE1-/- hearts with 1 mum nifedipine induced potentially anti-arrhythmic changes including: (1) restored epicardial APD90 (from 57.1 +/- 0.5 ms to 42.3 +/- 0.4 ms, P < 0.001; n = 5); (2) altered DeltaAPD90 to values (11.2 +/- 2.6) close to WT (P > 0.05; n = 5); (3) EAD suppression during both spontaneous activity and following cessation of ventricular pacing (n = 5) to give similar features to WT controls (n = 5); (4) suppression of programmed electrical stimulation-induced VT; and (5) suppression of APD alternans. These findings suggest arrhythmic effects of reduced outward currents expected in KCNE1-/- hearts and their abolition by antagonism of inward L-type Ca2+ current.

The KCNQ1 potassium channel: from gene to physiological function

The voltage-gated KCNQ1 (KvLQT1, Kv7.1) potassium channel plays a crucial role in shaping the cardiac action potential as well as in controlling the water and salt homeostasis in several epithelial tissues. KCNQ1 channels in these tissues are tightly regulated by auxiliary proteins and accessory factors, capable of modulating the properties of the channel complexes. This paper reviews the current knowledge about the KCNQ1 channel with a major focus on interacting proteins and physiological functions.

The corticosteroid hormone induced factor: a new modulator of KCNQ1 channels?

The corticosteroid hormone induced factor (CHIF) is a member of the one-transmembrane segment protein family named FXYD, which also counts phospholemman and the Na,K-pump gamma-subunit. Originally it was suggested that CHIF could induce the expression of the I(Ks) current when expressed in Xenopus laevis oocytes, but recently CHIF has attracted attention as a modulatory subunit of the Na,K-pump. In renal and intestinal epithelia, the expression of CHIF is dramatically up-regulated in response to aldosterone stimulation, and regulation of epithelial ion channels by CHIF is an attractive hypothesis. To study a potential regulatory effect of the CHIF subunit on KCNQ1 channels, co-expression experiments were performed in Xenopus laevis oocytes and mammalian CHO-K1 cells. Electrophysiological characterization was obtained by two-electrode voltage-clamp and patch-clamp, respectively. In both expression systems, we find that CHIF drastically modulates the KCNQ1 current; in the presence of CHIF, the KCNQ1 channels open at all membrane potentials. Thereby, CHIF is the first accessory subunit shown to be capable of modulating both the Na,K-pump and an ion channel. To find a possible physiological function of the constitutively open KCNQ1/CHIF complex, the precise localization of KCNQ1 and CHIF in distal colon and kidney from control and salt-depleted rats was determined by confocal microscopy. However, in these tissues, we did not detect an obvious overlap in expression between KCNQ1 and CHIF. In conclusion, the hormone-regulated subunit CHIF modulates the voltage sensitivity of the KCNQ channels, but so far evidence for an actual co-localization of CHIF and KCNQ1 channels in native tissue is lacking.

Genetic Deletion of the A 1 Adenosine Receptor Limits Myocardial Ischemic Tolerance

Adenosine receptors may be important determinants of intrinsic ischemic tolerance. Genetically modified mice were used to examine effects of global A 1 adenosine receptor (A 1 AR) knockout (KO) on function and ischemic tolerance in perfused mouse hearts. Baseline contractile function and heart rate were unaltered by A 1 AR KO, which was shown to abolish the negative chronotropic effects of 2-chloroadenosine (A 1 AR-mediated) without altering A 2 adenosine receptor–mediated coronary dilation. Tolerance to 25 minutes global normothermic ischemia (followed by 45 minutes reperfusion) was significantly limited by A 1 AR KO, with impaired contractile recovery (reduced by ≈25%) and enhanced lactate dehydrogenase (LDH) efflux (increased by ≈100%). Functional effects of A 1 AR KO involved worsened systolic pressure development with little to no change in diastolic dysfunction. In contrast, cardiac specific A 1 AR overexpression enhanced ischemic tolerance with a primary action on diastolic dysfunction. Nonselective receptor agonism (10 μmol/L 2-chloroadenosine) protected wild-type and also A 1 AR KO hearts (albeit to a lesser extent), implicating protection via subtypes additional to A 1 ARs. However, A 1 AR KO abrogated effects of 2-chloroadenosine on ischemic contracture and diastolic dysfunction. These data are the first demonstrating global deletion of the A 1 AR limits intrinsic myocardial resistance to ischemia. Data indicate the function of intrinsically activated A 1 ARs appears primarily to be enhancement of postischemic contractility and limitation of cell death.

KCNQ1/KCNE1 channels during germ-cell differentiation in the rat: expression associated with testis pathologies

KCNQ1/KCNE1 channels are responsible for the Jervell-Lange-Nielsen cardiac syndrome, which is also characterized by congenital deafness. KCNQ1/KCNE1 is crucial for K+ transport in the inner ear. We show that KCNQ1 and KCNE1 are associated in testis and that their expression is closely regulated during development. Both genes were expressed in undifferentiated germ cells in 21-day-old rats and mostly confined to basal immature germ cells in adulthood. Leydig and Sertoli cells were negative. KCNQ1 and KCNE1 were also studied in various germ-cell pathologies. First, in spontaneous unilateral rat testis atrophy, hematoxylin-eosin analysis revealed massive germ-cell aplasia with only Sertoli cells and groups of interstitial Leydig cells. In these samples, KCNQ1 and KCNE1 were not expressed. In human seminoma samples characterized by a proliferation of undifferentiated germ cells, KCNQ1/KCNE1 protein levels were higher than in healthy samples. Our results demonstrate that the expression of KCNQ1 and KCNE1 is associated with early stages of spermatogenesis and with the presence of undifferentiated healthy or neoplastic germ cells. The presence of a K+ rich-fluid in the seminiferous tubule suggests that KCNQ1/KCNE1 is involved in K+ transport, probably during germ-cell development.

Molecular diversity and regulation of renal potassium channels

K(+) channels are widely distributed in both plant and animal cells where they serve many distinct functions. K(+) channels set the membrane potential, generate electrical signals in excitable cells, and regulate cell volume and cell movement. In renal tubule epithelial cells, K(+) channels are not only involved in basic functions such as the generation of the cell-negative potential and the control of cell volume, but also play a uniquely important role in K(+) secretion. Moreover, K(+) channels participate in the regulation of vascular tone in the glomerular circulation, and they are involved in the mechanisms mediating tubuloglomerular feedback. Significant progress has been made in defining the properties of renal K(+) channels, including their location within tubule cells, their biophysical properties, regulation, and molecular structure. Such progress has been made possible by the application of single-channel analysis and the successful cloning of K(+) channels of renal origin.

The MinK-related peptides

Voltage-gated potassium (Kv) channels mediate rapid, selective diffusion of K+ ions through the plasma membrane, controlling cell excitability, secretion and signal transduction. KCNE genes encode a family of single transmembrane domain proteins called MinK-related peptides (MiRPs) that function as ancillary or beta subunits of Kv channels. When co-expressed in heterologous systems, MiRPs confer changes in Kv channel conductance, gating kinetics and pharmacology, and are fundamental to recapitulation of the properties of some native currents. Inherited mutations in KCNE genes are associated with diseases of cardiac and skeletal muscle, and the inner ear. This article reviews our current understanding of MiRPs--their functional roles, the mechanisms underlying their association with Kv alpha subunits, their patterns of native expression and emerging evidence of the potential roles of MiRPs in the brain. The ubiquity of MiRP expression and their promiscuous association with Kv alpha subunits suggest a prominent role for MiRPs in channel dependent systems.

Genetic disorders of transporters/channels in the inner ear and their relation to the kidney

Inner ear physiology is reviewed with emphasis on features common to renal physiology. Genetic disorders in transporters/channels for chloride (ClC-K), bicarbonate (Cl(-)/HCO(3)(-) exchanger), protons (H(+)-ATPase), sodium (ENaC, NKKC1, NBC3, NHE3), potassium (KCNQ1/KCNE1, Kcc4), and water (AQP4) in the inner ear and their relation to the kidney are discussed. Based on data from human disorders (with or without mouse counterparts) and mouse models (without human counterparts) this article focuses on the involvement of these transporters/channels in hearing loss.

Heteromeric KCNE2/KCNQ1 potassium channels in the luminal membrane of gastric parietal cells

Recently, we and others have shown that luminal K+ recycling via KCNQ1 K+ channels is required for gastric H+ secretion. Inhibition of KCNQ1 by the chromanol 293B strongly diminished H+ secretion. The present study aims at clarifying KCNQ1 subunit composition, subcellular localization, regulation and pharmacology in parietal cells. Using in situ hybridization and immunofluorescence techniques, we identified KCNE2 as the beta subunit of KCNQ1 in the luminal membrane compartment of parietal cells. Expressed in COS cells, hKCNE2/hKCNQ1 channels were activated by acidic pH, PIP2, cAMP and purinergic receptor stimulation. Qualitatively similar results were obtained in mouse parietal cells. Confocal microscopy revealed stimulation-induced translocation of H+,K+-ATPase from tubulovesicles towards the luminal pole of parietal cells, whereas distribution of KCNQ1 K+ channels did not change to the same extent. In COS cells the 293B-related substance IKs124 blocked hKCNE2/hKCNQ1 with an IC50 of 8 nM. Inhibition of hKCNE1- and hKCNE3-containing channels was weaker with IC50 values of 370 and 440 nM, respectively. In conclusion, KCNQ1 coassembles with KCNE2 to form acid-activated luminal K+ channels of parietal cells. KCNQ1/KCNE2 is activated during acid secretion via several pathways but probably not by targeting of the channel to the membrane. IKs124 could serve as a leading compound in the development of subunit-specific KCNE2/KCNQ1 blockers to treat peptic ulcers.

Basolateral localisation of KCNQ1 potassium channels in MDCK cells: molecular identification of an N-terminal targeting motif

KCNQ1 potassium channels are expressed in many epithelial tissues as well as in the heart. In epithelia KCNQ1 channels play an important role in salt and water transport and the channel has been reported to be located apically in some cell types and basolaterally in others. Here we show that KCNQ1 channels are located basolaterally when expressed in polarised MDCK cells. The basolateral localisation of KCNQ1 is not affected by co-expression of any of the five KCNE β-subunits. We characterise two independent basolateral sorting signals present in the N-terminal tail of KCNQ1. Mutation of the tyrosine residue at position 51 resulted in a non-polarized steady-state distribution of the channel. The importance of tyrosine 51 in basolateral localisation was emphasized by the fact that a short peptide comprising this tyrosine was able to redirect the p75 neurotrophin receptor, an otherwise apically located protein, to the basolateral plasma membrane. Furthermore, a di-leucine-like motif at residues 38-40 (LEL) was found to affect the basolateral localisation of KCNQ1. Mutation of these two leucines resulted in a primarily intracellular localisation of the channel.

Postural and locomotor control in normal and vestibularly deficient mice

We investigated how vestibular information is used to maintain posture and control movement by studying vestibularly deficient mice (IsK-/- mutant). In these mutants, microscopy showed degeneration of the cristae of the semicircular canals and of the maculae of the utriculi and sacculi, while behavioural and vestibulo-ocular reflex testing showed that vestibular function was completely absent. However, the histology of Scarpa's ganglia and the vestibular nerves was normal in mutant mice, indicating the presence of intact central pathways. Using X-ray and high-speed cineradiography, we compared resting postures and locomotion patterns between these vestibularly deficient mice and vestibularly normal mice (wild-type and IsK+/-). The absence of vestibular function did not affect resting posture but had profound effects on locomotion. At rest, the S-shaped, sagittal posture of the vertebral column was the same for wild-type and mutant mice. Both held the head with the atlanto-occipital joint fully flexed, the cervico-thoracic junction fully flexed, and the cervical column upright. Wild-type mice extended the head and vertebral column and could walk in a straight line. In marked contrast, locomotion in vestibularly deficient mice was characterized by circling episodes, during which the vertebral column maintained an S-shaped posture. Thus, vestibular information is not required to control resting posture but is mandatory for normal locomotion. We propose that vestibular inputs are required to signal the completion of a planned trajectory because mutant mice continued rotating after changing heading direction. Our findings support the hypothesis that vertebrates limit the number of degrees of freedom to be controlled by adopting just a few of the possible skeletal configurations.

Electrogram prolongation and nifedipine-suppressible ventricular arrhythmias in mice following targeted disruption of KCNE1

Mutations in KCNE1, the gene encoding the beta subunit of the slowly activating delayed rectifier potassium current (IKs) channel protein, may lead to the long QT syndrome (LQTS), a condition associated with enhanced arrhythmogenesis. Mice with homozygous deletion of the coding sequence of KCNE1 have inner ear defects strikingly similar to those seen in the corresponding human condition. The present study demonstrated and assessed the mechanism of ventricular arrhythmias in Langendorff-perfused whole heart preparations from homozygous KCNE1-/- mice compared to wild-type mice of the same age. The effects of programmed electrical stimulation with decremental pacing from the basal right ventricular epicardial surface upon electrogram waveforms recorded from the basal left ventricle were assessed and quantified using techniques of paced electrogram fractionation analysis for the first time in an experimental system. All KCNE1-/-(n = 10) but not wild-type (n = 14) mouse hearts empirically demonstrated marked pacing-induced ventricular arrhythmogenicity. This correlated with significant increases in electrogram dispersion, consistent with a wider spread in conduction velocities, in parallel with clinical findings from LQTS patients with potassium channel mutations. In contrast, introduction of 100 nM isoprenaline induced arrhythmogenicity in both KCNE1-/- (n = 7) and wild-type (n = 6) hearts during pacing. Furthermore, pretreatment with 1 muM nifedipine exerted a strong anti-arrhythmic effect in the KCNE1-/- hearts (n = 12) that persisted even in the presence of 100 nM isoprenaline (n = 6). Our findings associate KCNE1-/- with an arrhythmogenic phenotype that shows an increased dispersion of conduction velocities, and whose initiation is prevented by nifedipine, a finding that in turn may have therapeutic applications in conditions such as LQTS.

Altered properties of volume-sensitive osmolyte and anion channels (VSOACs) and membrane protein expression in cardiac and smooth muscle myocytes from Clcn3-/- mice

ClC-3, a member of the large superfamily of ClC voltage-dependent Cl(-) channels, has been proposed as a molecular candidate responsible for volume-sensitive osmolyte and anion channels (VSOACs) in some cells, including heart and vascular smooth muscle. However, the reported presence of native VSOACs in at least two cell types from transgenic ClC-3 disrupted (Clcn3(-/-)) mice casts considerable doubt on this proposed role for ClC-3. We compared several properties of native VSOACs and examined mRNA transcripts and membrane protein expression profiles in cardiac and pulmonary arterial smooth muscle cells from Clcn3(+/+) and Clcn3(-/-) mice to: (1) test the hypothesis that native VSOACs are unaltered in cells from Clcn3(-/-) mice, and (2) test the possibility that targeted inactivation of the Clcn3 gene using a conventional murine global knock-out approach may result in compensatory changes in expression of other membrane proteins. Our experiments demonstrate that VSOAC currents in myocytes from Clcn3(+/+) and Clcn3(-/-) mice are remarkably similar in terms of activation and inactivation kinetics, steady-state current densities, rectification, anion selectivity (I(-) > Cl(-)>> Asp(-)) and sensitivity to block by glibenclamide, niflumic acid, DIDS and extracellular ATP. However, additional experiments revealed several significant differences in other fundamental properties of native VSOACs recorded from atrial and smooth muscle cells from Clcn3(-/-) mice, including: differences in regulation by endogenous protein kinase C, differential sensitivity to block by anti-ClC-3 antibodies, and differential sensitivities to [ATP](i) and free [Mg(2+)](i). These results suggest that in response to Clcn3 gene deletion, there may be compensatory changes in expression of other proteins that alter VSOAC channel subunit composition or associated regulatory subunits that give rise to VSOACs with different properties. Consistent with this hypothesis, in atria from Clcn3(-/-) mice compared to Clcn3(+/+) mice, quantitative analysis of ClC mRNA expression levels revealed significant increases in transcripts for ClC-1, ClC-2, and ClC-3, and protein expression profiles obtained using two-dimensional polyacrylamide gel electrophoresis revealed complex changes in at least 35 different unidentified membrane proteins in cells from Clcn3(-/-) mice. These findings emphasize that caution needs to be exercised in simple attempts to interpret the phenotypic consequences of conventional global Clcn3 gene inactivation.

Inherited Arrhythmogenic Diseases

Twelve years after the identification of the molecular bases of the long-QT syndrome, it is now possible to express some considerations on the impact that genetic findings have had in the understanding of inherited arrhythmogenic diseases. Along with the excitement for the emerging data on genotype/phenotype correlation and for the development of the first recommendations for gene-specific management of patients, it is also important to acknowledge the unexpected complexity that has emerged. The focus of this article is to analyze the elusive aspects of the relationship between genetic defects and clinical manifestations and to propose some research directions that may provide the needed answers to move forward in the understanding of the genetics of heart rhythm abnormalities.

Cardiac channelopathies: from men to mice

During recent years, genetic manipulations in the mouse aimed to settle animal models of cardiac channelopathies. Among this group of diseases, the genetically heterogeneous long-QT (LQT) syndrome has instigated several models. Models of the LQT1 syndrome have been obtained by invalidation of Kcnq1 encoding a voltage-dependent K+ channel alpha-subunit, LQT2 syndrome by invalidation of Merg also encoding a voltage-dependent K+ channel alpha-subunit, LQT3 by knocking-in a gain-of-function deletion (delta KPQ) of the Scn5A cardiac Na+ channel gene, LQT4 by invalidating the ankyrin B gene. LQT5 by invalidating the Kcne1 K+ channel beta-subunit and the Andersen syndrome by invalidation of the KCNJ2 gene encoding for a cardiac inward rectifier K+ channel. Among these LQT models, the LQT3 and LQT4 mice exhibit spontaneous or exercise-induced life-threatening arrhythmias characteristics of long-QT patients. In addition, a model for the SCN5A-linked Brugada syndrome and for the inherited Lenègre disease has been established by heterozygous knock-out of Scn5A. These mice demonstrate progressive cardiac conduction defect similar to that observed in Lenègre patients and an increased susceptibility to arrhythmias as found in Brugada patients. In the future, the mouse model should prove instrumental to investigate the myocardial remodeling that is likely to result from gene invalidation either in man or in mice.

KCNQ1 channels sense small changes in cell volume

Many important physiological processes involve changes in cell volume, e.g. the transport of salt and water in epithelial cells and the contraction of cardiomyocytes. In this study, we show that voltage-gated KCNQ1 channels, which are strongly expressed in epithelial cells or cardiomyocytes, and KCNQ4 channels, expressed in hair cells and the auditory tract, are tightly regulated by small cell volume changes when co-expressed with aquaporin 1 water-channels (AQP1) in Xenopus oocytes. The KCNQ1 and KCNQ4 current amplitudes precisely reflect the volume of the oocytes. By contrast, the related KCNQ2 and KCNQ3 channels, which are prominently expressed in neurons, are insensitive to cell volume changes. The sensitivity of the KCNQ1 and KCNQ4 channels to cell volume changes is independent of the presence of the auxiliary KCNE1-3 subunits, although modulated by KCNE1 in the case of KCNQ1. Incubation of the oocytes in cytochalasin D and experiments with truncated KCNQ1 channels suggest that KCNQ1 channels sense cell volume changes through interactions between the cytoskeleton and the N-terminus of the channel protein. From our results we propose that KCNQ1 and KCNQ4 channels play an important role in cell volume control, e.g. during transepithelial transport of salt and water.

p11, an annexin II subunit, an auxiliary protein associated with the background K+ channel, TASK-1

TASK-1 belongs to the 2P domain K+ channel family and is the prototype of background K+ channels that set the resting membrane potential and tune action potential duration. Its activity is highly regulated by hormones and neurotransmitters. Although numerous auxiliary proteins have been described to modify biophysical, pharmacological and expression properties of different voltage- and Ca2+-sensitive K+ channels, none of them is known to modulate 2P domain K+ channel activity. We show here that p11 interacts specifically with the TASK-1 K+ channel. p11 is a subunit of annexin II, a cytoplasmic protein thought to bind and organize specialized membrane cytoskeleton compartments. This association with p11 requires the integrity of the last three C-terminal amino acids, Ser-Ser-Val, in TASK-1. Using series of C-terminal TASK-1 deletion mutants and several TASK-1-GFP chimeras, we demonstrate that association with p11 is essential for trafficking of TASK-1 to the plasma membrane. p11 association with the TASK-1 channel masks an endoplasmic reticulum retention signal identified as Lys-Arg-Arg that precedes the Ser-Ser-Val sequence.