ABSTRACT
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.
ABSTRACT
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.
