ABSTRACT
We present a unique case of a 60-year-old male with congestive heart failure who was admitted for a pre-syncopal episode and found to be in atrial fibrillation with rapid ventricular response (RVR). In order to effectively rate control the patient, he was administered an amiodarone bolus and intravenous (IV) infusion over 24 hours, along with a single oral 200 mg dose the following day. The patient subsequently developed acute hepatotoxicity along with features of acute kidney injury (AKI), pulmonary distress, and leukocytosis. After ruling out other etiologies for acute liver, pulmonary, and kidney injury, amiodarone-induced multi-organ toxicity was suspected and amiodarone was discontinued. Within hours of amiodarone discontinuation, the patient's clinical status and organ function improved remarkably. In the setting of a patient being treated with IV amiodarone and presenting with sudden signs of dyspnea, acute elevation of transaminases and AKI within one to two days of initial dosing, acute amiodarone-induced organ toxicity should be considered.
ABSTRACT
Sodium-dependent transporters couple the flow of Na+ ions down their electrochemical potential gradient to the uphill transport of various ligands. Many of these transporters share a common core structure composed of a five-helix inverted repeat and deliver their cargo utilizing an alternating-access mechanism. A detailed characterization of inward-facing conformations of the Na+-dependent sugar transporter from Vibrio parahaemolyticus (vSGLT) has previously been reported, but structural details on additional conformations and on how Na+ and ligand influence the equilibrium between other states remains unknown. Here, double electron-electron resonance spectroscopy, structural modeling, and molecular dynamics are utilized to deduce ligand-dependent equilibria shifts of vSGLT in micelles. In the absence and presence of saturating amounts of Na+, vSGLT favors an inward-facing conformation. Upon binding both Na+ and sugar, the equilibrium shifts toward either an outward-facing or occluded conformation. While Na+ alone does not stabilize the outward-facing state, gating charge calculations together with a kinetic model of transport suggest that the resting negative membrane potential of the cell, absent in detergent-solubilized samples, may stabilize vSGLT in an outward-open conformation where it is poised for binding external sugars. In total, these findings provide insights into ligand-induced conformational selection and delineate the transport cycle of vSGLT.
