A New Normal: Assessment Outcomes and Recommendations for Virtual Versus In-Person Curricula in Post-COVID-19 Times.

Introduction: COVID-19 response efforts that began in March 2020 prompted an urgent need to transition medical education from an in-person to a virtual format. Our aim is to provide evaluation of a virtual platform for a fully integrated curriculum to provide future guidance in teaching methods. Materials and Methods: We used summative assessments and course evaluations from pre- and post-transition from in-person to virtual delivery of educational content to measure the impacts of this transition on student performance and perceptions. Additionally, we surveyed students about their in-person versus online educational preferences. Results: There were no statistically significant differences in student knowledge acquisition as assessed by weighted averages of summative assessments when comparing an in-person to a virtual educational platform. While the transition to virtual learning was initially well-received by students, our studied cohorts gave lower scores for the overall learning experience after prolonged virtual learning (p < 0.001). Students had a strong preference that anatomy and other group sessions should be delivered in-person. There was no strong preference whether other learning modalities should be given in-person or virtually. Conclusions: Although student knowledge acquisition remained stable on a virtual platform, the student learning experience varied. We recommend that when returning to a new normal after COVID-19 restrictions are lifted, sessions that require 3-dimensional or group learning should remain in-person, while other educational activities may be offered on a virtual platform and that, whenever virtual learning is employed, attention be paid to ensuring ongoing social and academic engagement between learners and faculty.

Dual role of junctin in the regulation of ryanodine receptors and calcium release in cardiac ventricular myocytes.

Junctin, a 26 kDa intra-sarcoplasmic reticulum (SR) protein, forms a quaternary complex with triadin, calsequestrin and the ryanodine receptor (RyR) at the junctional SR membrane. The physiological role for junctin in the luminal regulation of RyR Ca(2+) release remains unresolved, but it appears to be essential for proper cardiac function since ablation of junctin results in increased ventricular automaticity. Given that the junctin levels are severely reduced in human failing hearts, we performed an in-depth study of the mechanisms affecting intracellular Ca(2+) homeostasis in junctin-deficient cardiomyocytes. In concurrence with sparks, JCN-KO cardiomyocytes display increased Ca(2+) transient amplitude, resulting from increased SR [Ca(2+)] ([Ca(2+)](SR)). Junctin ablation appears to affect how RyRs 'sense' SR Ca(2+) load, resulting in decreased diastolic SR Ca(2+) leak despite an elevated [Ca(2+)](SR). Surprisingly, the ß-adrenergic enhancement of [Ca(2+)](SR) reverses the decrease in RyR activity and leads to spontaneous Ca(2+) release, evidenced by the development of spontaneous aftercontractions. Single channel recordings of RyRs from WT and JCN-KO cardiac SR indicate that the absence of junctin produces a dual effect on the normally linear response of RyRs to luminal [Ca(2+)]: at low luminal [Ca(2+)] (<1 mmol l(-1)), junctin-devoid RyR channels are less responsive to luminal [Ca(2+)]; conversely, high luminal [Ca(2+)] turns them hypersensitive to this form of channel modulation. Thus, junctin produces complex effects on Ca(2+) sparks, transients, and leak, but the luminal [Ca(2+)]-dependent dual response of junctin-devoid RyRs demonstrates that junctin normally acts as an activator of RyR channels at low luminal [Ca(2+)], and as an inhibitor at high luminal [Ca(2+)]. Because the crossover occurs at a [Ca(2+)](SR) that is close to that present in resting cells, it is possible that the activator-inhibitor role of junctin may be exerted under periods of prevalent parasympathetic and sympathetic activity, respectively.

The mitochondrial ryanodine receptor in rat heart: a pharmaco-kinetic profile.

A protein discovered within inner mitochondrial membranes (IMM), designated as the mitochondrial ryanodine receptor (mRyR), has been recognized recently as a modulator of Ca(2+) fluxes in mitochondria. The present study provides fundamental pharmacological and electrophysiological properties of this mRyR. Rat cardiac IMM fused to lipid bilayers revealed the presence of a mitochondrial channel with gating characteristics similar to those of classical sarcoplasmic reticulum RyR (SR-RyR), but a variety of other mitochondrial channels obstructed clean recordings. Mitochondrial vesicles were thus solubilized and subjected to sucrose sedimentation to obtain mRyR-enriched fractions. Reconstitution of sucrose-purified fractions into lipid bilayers yielded Cs(+)-conducting, Ca(2+)-sensitive, large conductance (500-800 pS) channels with signature properties of SR-RyRs. Cytosolic Ca(2+) increased the bursting frequency and mean open time of the channel. Micromolar concentrations of ryanodine induced the appearance of subconductance states or inhibited channel activity altogether, while Imperatoxin A (IpTx(a)), a specific activator of RyRs, reversibly induced the appearance of distinct subconductance states. Remarkably, the cardiac mRyR displayed a Ca(2+) dependence of [(3)H]ryanodine binding curve similar to skeletal RyR (RyR1), not cardiac RyR (RyR2). Overall, the mRyR displayed elemental attributes that are present in single channel lipid bilayer recordings of SR-RyRs, although some exquisite differences were also noted. These results therefore provide the first direct evidence that a unique RyR occurs in mitochondrial membranes.

Sarcoplasmic reticulum calcium overloading in junctin deficiency enhances cardiac contractility but increases ventricular automaticity.

BACKGROUND: Abnormal sarcoplasmic reticulum calcium (Ca) cycling is increasingly recognized as an important mechanism for increased ventricular automaticity that leads to lethal ventricular arrhythmias. Previous studies have linked lethal familial arrhythmogenic disorders to mutations in the ryanodine receptor and calsequestrin genes, which interact with junctin and triadin to form a macromolecular Ca-signaling complex. The essential physiological effects of junctin and its potential regulatory roles in sarcoplasmic reticulum Ca cycling and Ca-dependent cardiac functions, such as myocyte contractility and automaticity, are unknown. METHODS AND RESULTS: The junctin gene was targeted in embryonic stem cells, and a junctin-deficient mouse was generated. Ablation of junctin was associated with enhanced cardiac function in vivo, and junctin-deficient cardiomyocytes exhibited increased contractile and Ca-cycling parameters. Short-term isoproterenol stimulation elicited arrhythmias, including premature ventricular contractions, atrioventricular heart block, and ventricular tachycardia. Long-term isoproterenol infusion also induced premature ventricular contractions and atrioventricular heart block in junctin-null mice. Further examination of the electrical activity revealed a significant increase in the occurrence of delayed afterdepolarizations. Consistently, 25% of the junctin-null mice died by 3 months of age with structurally normal hearts. CONCLUSIONS: Junctin is an essential regulator of sarcoplasmic reticulum Ca release and contractility in normal hearts. Ablation of junctin is associated with aberrant Ca homeostasis, which leads to fatal arrhythmias. Thus, normal intracellular Ca cycling relies on maintenance of junctin levels and an intricate balance among the components in the sarcoplasmic reticulum quaternary Ca-signaling complex.

Altered Ca2+ sparks and gating properties of ryanodine receptors in aging cardiomyocytes.

To investigate the cellular mechanisms for altered cardiac function in senescence, we measured Ca(2+) transients and Ca(2+) sparks in ventricular cardiomyocytes from 6- to 24-month-old Fisher 344 (F344) rat hearts. The single channel properties of ryanodine receptors from adult and senescent hearts were also studied. In senescent myocytes, we observed a decreased peak [Ca(2+)](i) amplitude and an increased time constant for decay (tau), both of which correlated with a reduced Ca(2+) content of the sarcoplasmic reticulum (SR). Our studies also revealed that senescent cardiomyocytes had an increased frequency of Ca(2+) sparks and a slight but statistically significant decrease in average amplitude, full-width-at-half-maximum (FWHM) and full-duration-at-half-maximum (FDHM). Single channel recordings of ryanodine receptors (RyR2) demonstrated that in aging hearts, the open probability (P(o)) of RyR2 was increased but the mean open time was shorter, providing a molecular correlate for the increased frequency of Ca(2+) sparks and decreased size of sparks, respectively. Thus, modifications of normal RyR2 gating properties may play a role in the altered Ca(2+) homeostasis observed in senescent myocytes.