Rab11-dependent Recycling of the Human Ether-a-go-go-related Gene (hERG) Channel.

The human ether-a-go-go-related gene (hERG) encodes the pore-forming subunit of the rapidly activating delayed rectifier potassium channel (IKr). A reduction in the hERG current causes long QT syndrome, which predisposes affected individuals to ventricular arrhythmias and sudden death. We reported previously that hERG channels in the plasma membrane undergo vigorous internalization under low K(+) conditions. In the present study, we addressed whether hERG internalization occurs under normal K(+) conditions and whether/how internalized channels are recycled back to the plasma membrane. Using patch clamp, Western blot, and confocal imaging analyses, we demonstrated that internalized hERG channels can effectively recycle back to the plasma membrane. Low K(+)-enhanced hERG internalization is accompanied by an increased rate of hERG recovery in the plasma membrane upon reculture following proteinase K-mediated clearance of cell-surface proteins. The increased recovery rate is not due to enhanced protein synthesis, as hERG mRNA expression was not altered by low K(+) exposure, and the increased recovery was observed in the presence of the protein biosynthesis inhibitor cycloheximide. GTPase Rab11, but not Rab4, is involved in the recycling of hERG channels. Interfering with Rab11 function not only delayed hERG recovery in cells after exposure to low K(+) medium but also decreased hERG expression and function in cells under normal culture conditions. We concluded that the recycling pathway plays an important role in the homeostasis of plasma membrane-bound hERG channels.

Glycyrrhizic acid induced acquired apparent mineralocorticoid excess syndrome with a hyperadrenergic state: a case report.

BACKGROUND: Syndrome of apparent mineralocorticoid excess (AME) is characterized by excessive MR stimulation despite low levels of aldosterone. 11Beta-hydroxysteroid dehydrogenase-2 (11ßDSH-2) inactivates cortisol to cortisone, preventing cortisol-induced MR activation. Genetic defects in 11ßDSH-2 cause AME through accumulation of cortisol in the distal nephron, leading to MR activation induced hypertension, hypokalemia and metabolic alkalosis. Acquired AME can occur due to the ingestion of glycyrrhizic acid, found in licorice root, which inhibits 11ßDSH-2 and has additional effects on cortisol homeostasis through inhibition of 11ßDSH-1. CASE REPORT: We present a case of acquired AME with a hyperadrenergic symptoms induced by ingestion of Advanced Liver Support, a nutritional supplement produced by Advanced BioNutritionals(R), in a 65-year-old Caucasian female who presented with accelerated hypertension, hypokalemia, metabolic alkalosis and adrenergic symptoms. Cessation of the licorice-containing supplement resulted in complete resolution of the patient's hypertension, symptoms and abnormal lab values. To our knowledge this is the first reported case of AME from this supplement, and the first to describe accompanying hyperadrenergic symptoms. CONCLUSIONS: Glycyrrhizic acid is increasingly being found in unregulated nutritional supplements and has the potential to induce a reversable syndrome of AME. Acquired AME should be suspected in individuals who present with hypertension along with hypokalemia, metabolic alkalosis and low plasma renin and serum aldosterone levels.

A case of native tricuspid valve Neisseria mucosa/sicca species infective endocarditis complicated by septic pulmonary emboli.

We report a rare case of native tricuspid valve infective endocarditis caused by Neisseria mucosa/sicca, a gram-negative diplococcus which colonizes the upper respiratory tract. A female in her late 20 s with a history of injection drug use (IDU) who recently completed treatment for methicillin-sensitive Staphylococcus aureus (MSSA) native tricuspid valve infective endocarditis presented to the hospital with a 6-week history of increasing chest pain, shortness of breath and night sweats. Blood cultures grew Neisseria mucosa/sicca species in 3 of 3 sets. Transthoracic echocardiogram showed a large 3 cm × 2.2 cm vegetation on the tricuspid valve with severe regurgitation. The patient was initially treated with ceftriaxone and gentamicin. Her case was complicated by ongoing septic pulmonary emboli ultimately require pulmonary endarterectomy and repair of her tricuspid valve. We hope this case highlights a rare but known cause of infective endocarditis especially in patients with a history of IDU who may lick their needles, which predisposes those individuals to intravenous introduction of oral bacteria.

Anti-Ro52 antibody acts on the S5-pore linker of hERG to chronically reduce channel expression.

AIMS: The human ether-a-go-go-related gene (hERG) encodes the rapidly activating delayed rectifier potassium channel (IKr). Malfunction of hERG/IKr is the primary cause of acquired long QT syndrome (LQTS), an electrical disorder of the heart that can cause arrhythmias and sudden death. Patients with autoimmune diseases display a high incidence of LQTS. While dysfunction of hERG channels induced by autoantibodies such as anti-Ro52 may play a role in this pathology, the underlying mechanisms are not well understood. Here, we investigated the acute and chronic effects of anti-Ro52 antibody on hERG channels stably expressed in human embryonic kidney (hERG-HEK) 293 cells as well as IKr in neonatal rat ventricular myocytes. METHODS AND RESULTS: Using whole-cell patch clamp, western blot analyses, and immunocytochemistry, we found that a 12-h treatment of hERG-HEK cells with patients' sera containing anti-Ro52 autoantibody decreased the hERG current (IhERG) by 32% compared to cells treated with autoantibody-negative patients' sera. Commercial anti-Ro52 antibody at 100 µg/mL did not acutely block IhERG. Instead, a 12-h treatment with anti-Ro52 antibody at a concentration of 4 µg/mL significantly reduced mature hERG protein expression and IhERG. Specifically, anti-Ro52 antibody did not acutely block hERG current but chronically facilitated hERG endocytic degradation. The extracellular S5-pore linker of hERG, which forms the turret of the channel on the outside of the cell, is the target region for anti-Ro52-mediated hERG reduction since its replacement with the analogous region of EAG abolished the anti-Ro52 effect. In neonatal rat ventricular myocytes, 100 µg/mL anti-Ro52 antibody did not acutely block IKr, but a 12-h treatment of cells with 4 µg/mL anti-Ro52 antibody selectively reduced IKr and prolonged the action potential duration. CONCLUSIONS: Our results indicate that anti-Ro52 antibody acts on the hERG S5-pore linker to chronically decrease hERG expression and current. These findings provide novel insights into hERG regulation and anti-Ro52 antibody-associated LQTS.