BACKGROUND: The Htr3a antagonist, ondansetron, has been reported to prolong the QT interval and induce Torsades de pointes in the treatment of postoperative nausea and vomiting. To explore the mechanisms underlying these findings, we examined the effects of ondansetron on the mouse cardiac voltage-gated K⁺ (Kv) channel. METHODS AND RESULTS: Ondansetron increased QT intervals in late pregnant (LP) mice. We measured the Kv channels in freshly isolated left ventricular (LV) myocytes from non-pregnant (NP) and late pregnant (LP) mice, using patch-clamp electrophysiology. Ondansetron blocked Kv current at a dose of 50 µM, and reduced the amplitude of peak current densities in a dose-dependent manner (0, 1, 5, 50 µM), in LP but not in NP mice. In contrast, serotonin and the Htr3 agonist, m-CPBG, increased Kv current densities in NP, but not in LP mice. Interestingly, during pregnancy, serum serotonin levels were markedly increased, suggesting the saturation of the effect of serotonin. Immunostaning data showed that Kv4.3 protein and Htr3a co-localize at the membrane and t-tubule of cardiomyocytes. Moreover, Kv4.3 membrane trafficking was enhanced in response to Htr3a-mediated serotonin stimulation in NP, but not in LP mice. Membrane analysis showed that serotonin enhances Kv4.3 membrane trafficking in NP, but not LP mice. CONCLUSION: Ondansetron reduced Kv current densities, and reduced the Kv4.3 membrane trafficking in LP mouse ventricular cardiomyocytes. This data suggests that QT prolongation by ondansetron is mediated by the reduction of Kv current densities and Kv4.3 membrane trafficking.
Animals ; Electrophysiology ; Membranes ; Mice* ; Muscle Cells* ; Myocytes, Cardiac ; Ondansetron* ; Postoperative Nausea and Vomiting ; Pregnancy ; Serotonin ; Torsades de Pointes

In this study, the Autokit Total Ketone Bodies kit (Wako Pure Chemical, Japan), a total ketone measurement assay using an enzymatic method, was evaluated using a Roche Cobas e702 instrument (Roche Diagnostics, Germany). Precision, linearity, carryover, and reference range verification were evaluated with reference to Clinical Laboratory Standards Institute guidelines. Standard materials provided by the manufacturer and patient samples were used for the evaluation. The precision and carryover of the evaluation result satisfied the acceptance criteria. Linearity was also acceptable at more than 0.99. The quantitative Autokit Total Ketone Bodies kit is precise, and can be widely used in clinical laboratories.
3-Hydroxybutyric Acid ; Evaluation Studies as Topic ; Humans ; Ketone Bodies* ; Methods ; Reference Values

PURPOSE: The mechanisms underlying repolarization abnormalities during pregnancy are not fully understood. Although maternal serotonin (5-hydroxytryptamine, 5-HT) production is an important determinant for normal fetal development in mice, its role in mothers remains unclear. We evaluated the role of serotonin in ventricular repolarization in mice hearts via 5Htr3 receptor (Htr3a) and investigated the mechanism of QT-prolongation during pregnancy. MATERIALS AND METHODS: We measured current amplitudes and the expression levels of voltage-gated K⁺ (Kv) channels in freshly-isolated left ventricular myocytes from wild-type non-pregnant (WT-NP), late-pregnant (WT-LP), and non-pregnant Htr3a homozygous knockout mice (Htr3a(−/−)-NP). RESULTS: During pregnancy, serotonin and tryptophan hydroxylase 1, a rate-limiting enzyme for the synthesis of serotonin, were markedly increased in hearts and serum. Serotonin increased Kv current densities concomitant with the shortening of the QT interval in WT-NP mice, but not in WT-LP and Htr3a(−/−)-NP mice. Ondansetron, an Htr3 antagonist, decreased Kv currents in WT-LP mice, but not in WT-NP mice. Kv4.3 directly interacted with Htr3a, and this binding was facilitated by serotonin. Serotonin increased the trafficking of Kv4.3 channels to the cellular membrane in WT-NP. CONCLUSION: Serotonin increases repolarizing currents by augmenting Kv currents. Elevated serotonin levels during pregnancy counterbalance pregnancy-related QT prolongation by facilitating Htr3-mediated Kv currents.
*Action Potentials/drug effects ; Animals ; Cell Membrane/drug effects/metabolism ; Disease Models, Animal ; Electrocardiography ; Female ; HSC70 Heat-Shock Proteins/metabolism ; HSP90 Heat-Shock Proteins/metabolism ; Heart Ventricles/drug effects/*metabolism ; Mice, Inbred C57BL ; Mice, Knockout ; Myocytes, Cardiac/drug effects/metabolism ; Potassium Channels/metabolism ; Pregnancy ; Rabbits ; Rats, Sprague-Dawley ; Receptors, Serotonin, 5-HT3/metabolism ; Serotonin/*metabolism ; Serotonin 5-HT3 Receptor Agonists/pharmacology

Serosurveillance studies reveal the actual disease burden and herd immunity level in the population. In Seoul, Korea, a cross-sectional investigation showed 0.07% anti-severe acute respiratory syndrome coronavirus-2 antibody seropositivity among 1,500 outpatients of the university hospitals. Low seroprevalence reflects well-implemented social distancing.Serosurveillance should be repeated as the pandemic progresses.