Diphenyleneiodonium (DPI) has been widely used as an inhibitor of NADPH oxidase (Nox) to discover its function in cardiac myocytes under various stimuli. However, the effects of DPI itself on Ca2+ signaling and contraction in cardiac myocytes under control conditions have not been understood. We investigated the effects of DPI on contraction and Ca2+ signaling and their underlying mechanisms using video edge detection, confocal imaging, and whole-cell patch clamp technique in isolated rat cardiac myocytes. Application of DPI suppressed cell shortenings in a concentration-dependent manner (IC50 of ≅0.17 µM) with a maximal inhibition of ~70% at ~100 µM. DPI decreased the magnitude of Ca2+ transient and sarcoplasmic reticulum Ca2+ content by 20%–30% at 3 µM that is usually used to remove the Nox activity, with no effect on fractional release. There was no significant change in the half-decay time of Ca2+ transients by DPI. The L-type Ca2+ current (ICa) was decreased concentration-dependently by DPI (IC50 of ≅40.3 µM) with ≅13.1%-inhibition at 3 µM. The frequency of Ca2+ sparks was reduced by 3 µM DPI (by ~25%), which was resistant to a brief removal of external Ca2+ and Na+. Mitochondrial superoxide level was reduced by DPI at 3–100 µM. Our data suggest that DPI may suppress L-type Ca2+ channel and RyR, thereby attenuating Ca2+-induced Ca2+ release and contractility in cardiac myocytes, and that such DPI effects may be related to mitochondrial metabolic suppression.

Background: The Covid-19 pandemic that occurred at the end of 2019, especially the fourth wave in Vietnam, has affected the world not only in terms of economy, society, and physical health but also affected the mental health of population in general and of medical students in particular. The use of different coping methods may be protective or risk factors for mental health problems. Objectives: 1. To investigate the prevalence of anxiety, stress, and depression among medical students during the Covid -19 pandemic 2. To describe several coping behavior among medical students during the pandemic. Subjects and methods: A descriptive cross-sectional study conducted on 2350 students of medicine programme range from the first year to the sixth year in the school year 2021 - 2022 at Hue University of Medicine and Pharmacy. Using the DASS-21 scale to survey anxiety, depression and stress in research subjects and a self-designed questionnaire to describe the coping methods of medical students. Results: out of 2350 sample, the prevelance of depression, anxiety, and stress was 38%, 33.2%, and 17% respectively. 13.8% had both anxiety and stress, 15.4% had both stress and depression, and 12.8% had a combination of anxiety, depression and stress. Coping behavior was commonly selected including: eating and sleeping regularly as usual (68.1%); doing exercise at home at least 5 days/week and 30 minutes/day (23.9%); 36.5% of students performed their favorite activities under appropriate conditions most of the time or often. In addition, 59.7% of students had learn new things on the internet, 4.5% of students had practiced meditation and relaxation, 2.9% of students had chosen to write a diary and things they were grateful for; 32% had still maintain contacted with friends via video calls, text messages and 34.4% had chosen to participate in volunteer activities. Conclusion: This study highlights a high rate of anxiety, stress and depression among medical students during the fouthth wave of the Covid-19 pandemic. Personal lifestyle changes and social activities were amongst the most comon coping behavior reported.