Cross-sectional study on public health knowledge among first-year university students in Japan: Implications for educators and educational institutions.

In recent years, there have been increasing knowledge gaps and biases in public health information. This has become especially evident during the COVID-19 pandemic and has contributed to the spread of misinformation. With constant exposure to disinformation and misinformation through television, the internet, and social media, even university students studying healthcare-related subjects lack accurate public health knowledge. This study aimed to assess university students' knowledge levels of basic public health topics before they started their specialized education. Participants in this cross-sectional study were first-year students from medical schools, health-related colleges, and liberal arts colleges. A self-administered electronic survey was conducted from April to May 2021 at a private university in Japan, comprising six colleges with seven programs. Data analysis, conducted from June to December 2022, included students' self-reported public health knowledge, sources of information, and self-assessment of knowledge levels. Among the 1,562 students who received the questionnaire, 549 (192 male [35%], 353 female [64.3%], and 4 undisclosed [0.7%]) responded to one question (participants' response rate for each question; 59.6%-100%). The results showed that students had limited public health knowledge, especially in sexual health topics, and 10% of students reported not learning in class before university admission the following 11 topics: two on Alcohol, Tobacco, and Other Drugs; eight on Growth, Development, and Sexual Health; and one on Personal and Community Health. These results indicate significant knowledge gaps and biases, as well as gender gaps, in public health education, especially in the area of sexual health, which may help educators and educational institutions to better understand and prepare for further specialized education. The findings also suggest a need to supplement and reinforce the foundation of public health knowledge for healthcare majors at the time of university admission.

Reduction of intracellular Mg2+ caused by reactive oxygen species in rat ventricular myocytes.

The concentration of intracellular free Mg2+ ([Mg2+]i) should be maintained strictly for the regulation of cellular functions. Since reactive oxygen species (ROS) are liable to increase in various pathological conditions and induce cellular damage, we investigated whether ROS affect intracellular Mg2+ homeostasis. We measured [Mg2+]i in ventricular myocytes from Wistar rats using the fluorescent indicator, mag-fura-2. The administration of hydrogen peroxide (H2O2) decreased [Mg2+]i in Ca2+-free Tyrode's solution. Intracellular free Mg2+ was also reduced by endogenous ROS as generated by pyocyanin, which was inhibited by pretreatment with n-acetyl cysteine (NAC). The rate of change in [Mg2+]i by 500 µM H2O2 in 5 min (on average, -0.61 µM/s) was independent of extracellular Na+, and intra- and extracellular Mg2+ concentrations. When extracellular Ca2+ was present, the rate of Mg2+ decrease was significantly reduced, on average, by ∼60%. The half-maximal effective concentration of H2O2 on the Mg2+ decrease was estimated to be between 400 and 425 µM. The Mg2+ decrease by H2O2 in the absence of Na+ was inhibited by 200 µM imipramine, a known inhibitor of Na+/Mg2+ exchange. We perfused rat hearts with the Ca2+-free Tyrode's solution containing H2O2 (500 µM, 5 min) on the Langendorff apparatus,. H2O2 stimulation increased Mg2+ concentration in the perfusate, suggesting the H2O2-induced decrease in [Mg2+]i was caused by Mg2+ extrusion. Collectively, these results suggest the existence of a Na+-independent Mg2+ efflux system activated by ROS in cardiomyocytes. The lower [Mg2+]i may in part be attributed to ROS-mediated cardiac dysfunction.

Effects of COVID-19 on Japanese medical students' knowledge and attitudes toward e-learning in relation to performance on achievement tests.

The COVID-19 pandemic forced many educational institutions to turn to electronic learning to allow education to continue under the stay-at-home orders/requests that were commonly instituted in early 2020. In this cross-sectional study, we evaluated the effects of the COVID-19 pandemic on medical education in terms of students' attitudes toward online classes and their online accessibility; additionally, we examined the impacts of any disruption caused by the pandemic on achievement test performance based on the test results. The participants were 674 students (412 in pre-clinical, 262 in clinical) at Juntendo University Faculty of Medicine; descriptive analysis was used to examine the respondents' characteristics and responses. The majority of respondents (54.2%) preferred asynchronous classes. Mann-Whitney U tests revealed that while pre-clinical students preferred asynchronous classes significantly more than clinical students (39.6%, p < .001), students who preferred face-to-face classes had significantly higher total achievement test scores (U = 1082, p = .021, r = .22). To examine the impacts of pandemic-induced changes in learning, we conducted Kruskal-Wallis tests and found that the 2020 and 2021 scores were significantly higher than those over the last three years. These results suggest that while medical students may have experienced challenges adapting to electronic learning, the impact of this means of study on their performance on achievement tests was relatively low. Our study found that if possible, face-to-face classes are preferable in an electronic learning environment. However, the benefit of asynchronous classes, such as those that allow multiple viewings, should continue to be recognized even after the pandemic.

Chronic magnesium deficiency causes reversible mitochondrial permeability transition pore opening and impairs hypoxia tolerance in the rat heart.

Chronic magnesium (Mg) deficiency induces and exacerbates various cardiovascular diseases. We previously investigated the mechanisms underlying decline in cardiac function caused by chronic Mg deficiency and the effectiveness of Mg supplementation on this decline using the Langendorff-perfused isolated mouse heart model. Herein, we used the Langendorff-perfused isolated rat heart model to demonstrate the chronic Mg-deficient rats (Mg-deficient group) had lower the heart rate (HR) and left ventricular pressure (LVDP) than rats with normal Mg levels (normal group). Furthermore, decline in cardiac function due to hypoxia/reoxygenation injury was significantly greater in the Mg-deficient group than in the normal group. Experiments on mitochondrial permeability transition pore (mPTP) using isolated mitochondria revealed that mitochondrial membrane was fragile in the Mg-deficient group, implying that cardiac function decline through hypoxia/reoxygenation injury is associated with mitochondrial function. Mg supplementation for chronic Mg-deficient rats not only improved hypomagnesemia but also almost completely restored cardiac and mitochondrial functions. Therefore, proactive Mg supplementation in pathological conditions induced by Mg deficiency or for those at risk of developing hypomagnesemia may suppress the development and exacerbation of certain disease states.

Langendorff Perfusion Method as an Ex Vivo Model to Evaluate Heart Function in Rats.

The Langendorff Perfused Heart Model is an experimental procedure developed at the end of the nineteenth century by Oskar Langendorff. In this procedure, an excised heart has a cannula inserted into its aorta so that the heart can be retrogradely perfused via the coronary artery. The procedure has been improved in recent times, and these improvements are used to evaluate the direct effect of medication on the heart as well as the effect of ischemia-reperfusion injury on heart function. In this chapter, we describe protocols for evaluating heart function in Langendorff perfused rat heart.

Increased reactive oxygen species, metabolic maladaptation, and autophagy contribute to pulmonary arterial hypertension-induced ventricular hypertrophy and diastolic heart failure.

Pulmonary arterial hypertension (PAH) is a debilitating and deadly disease with no known cure. Heart failure is a major comorbidity and a common cause of the premature death of patients with PAH. Increased asymmetrical right ventricular hypertrophy and septal wall thickening compress the left ventricular cavity and elicit diastolic heart failure. In this study, we used the Sugen5416/hypoxia/normoxia-induced PAH rat to determine whether altered pyridine nucleotide signaling in the failing heart contributes to 1) increased oxidative stress, 2) changes in metabolic phenotype, 3) autophagy, and 4) the PAH-induced failure. We found that increased reactive oxygen species, metabolic maladaptation, and autophagy contributed to the pathogenesis of right ventricular remodeling and hypertrophy that lead to left ventricular diastolic dysfunction. In addition, arterial elastance increased in PAH rats. Glucose-6-phosphate dehydrogenase is a major source of pyridine molecule (nicotinamide adenine dinucleotide phosphate), which is a substrate for nicotinamide adenine dinucleotide phosphate oxidases in the heart. Dehydroepiandrosterone, a 17-ketosteroid that reduces pulmonary hypertension and right ventricular hypertrophy, inhibited glucose-6-phosphate dehydrogenase, decreased oxidative stress, increased glucose oxidation and acetyl-coA, and reduced autophagy in the hearts of PAH rats. It also decreased arterial stiffness and improved left ventricular diastolic function. These findings demonstrate that pyridine nucleotide signaling, at least partly, mediates PAH-induced diastolic heart failure, and that reduction of glucose-6-phosphate dehydrogenase-derived nicotinamide adenine dinucleotide phosphate is beneficial to improve left ventricle diastolic function.

Glucose-6-phosphate dehydrogenase and NADPH redox regulates cardiac myocyte L-type calcium channel activity and myocardial contractile function.

We recently demonstrated that a 17-ketosteroid, epiandrosterone, attenuates L-type Ca(2+) currents (I(Ca-L)) in cardiac myocytes and inhibits myocardial contractility. Because 17-ketosteroids are known to inhibit glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway, and to reduce intracellular NADPH levels, we hypothesized that inhibition of G6PD could be a novel signaling mechanism which inhibit I(Ca-L) and, therefore, cardiac contractile function. We tested this idea by examining myocardial function in isolated hearts and Ca(2+) channel activity in isolated cardiac myocytes. Myocardial function was tested in Langendorff perfused hearts and I(Ca-L) were recorded in the whole-cell patch configuration by applying double pulses from a holding potential of -80 mV and then normalized to the peak amplitudes of control currents. 6-Aminonicotinamide, a competitive inhibitor of G6PD, increased pCO(2) and decreased pH. Additionally, 6-aminonicotinamide inhibited G6PD activity, reduced NADPH levels, attenuated peak I(Ca-L) amplitudes, and decreased left ventricular developed pressure and ±dp/dt. Finally, dialyzing NADPH into cells from the patch pipette solution attenuated the suppression of I(Ca-L) by 6-aminonicotinamide. Likewise, in G6PD-deficient mice, G6PD insufficiency in the heart decreased GSH-to-GSSG ratio, superoxide, cholesterol and acetyl CoA. In these mice, M-mode echocardiographic findings showed increased diastolic volume and end-diastolic diameter without changes in the fraction shortening. Taken together, these findings suggest that inhibiting G6PD activity and reducing NADPH levels alters metabolism and leads to inhibition of L-type Ca(2+) channel activity. Notably, this pathway may be involved in modulating myocardial contractility under physiological and pathophysiological conditions during which the pentose phosphate pathway-derived NADPH redox is modulated (e.g., ischemia-reperfusion and heart failure).

Whole-genome sequencing of liver cancers identifies etiological influences on mutation patterns and recurrent mutations in chromatin regulators.

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. We sequenced and analyzed the whole genomes of 27 HCCs, 25 of which were associated with hepatitis B or C virus infections, including two sets of multicentric tumors. Although no common somatic mutations were identified in the multicentric tumor pairs, their whole-genome substitution patterns were similar, suggesting that these tumors developed from independent mutations, although their shared etiological backgrounds may have strongly influenced their somatic mutation patterns. Statistical and functional analyses yielded a list of recurrently mutated genes. Multiple chromatin regulators, including ARID1A, ARID1B, ARID2, MLL and MLL3, were mutated in ∼50% of the tumors. Hepatitis B virus genome integration in the TERT locus was frequently observed in a high clonal proportion. Our whole-genome sequencing analysis of HCCs identified the influence of etiological background on somatic mutation patterns and subsequent carcinogenesis, as well as recurrent mutations in chromatin regulators in HCCs.

Mitochondrial K+ channels are involved in ischemic postconditioning in rat hearts.

The mitochondrial calcium-activated potassium channel (mitoK(Ca)) and the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) are both involved in cardiac preconditioning. Here, we examined whether these two channels are also involved in ischemic or pharmacological postconditioning. Using Langendorff perfusion, rat hearts were made hypoxic for 45 min and then reoxygenated for 30 min. Ischemic postconditioning (IPT) was achieved through application of 3 cycles of 10 s of reperfusion and 10 s of ischemia before reoxygenation, with and without paxilline (Pax; a mitoK(Ca) blocker) or 5-hydroxydecanoate (5-HD; a mitoK(ATP) blocker). Pharmacological postconditioning was carried out for 5 min at the onset of reoxygenation using NS1619 (a mitoK(Ca) opener) or diazoxide (Dia; a mitoK(ATP) opener). Pax and 5-HD abolished IPT-induced cardioprotection from reoxygenation injury, whereas administration of NS1619 or Dia significantly improved cardiac contractile activity and reduced aspartate aminotransferase (an index of myocyte injury) release following reoxygenation. In addition, isolated rat myocytes were loaded with tetramethylrhodamine methyl ester (TMRE; fluorescent mitochondrial membrane potential indicator) and 2',7'-dichlorofluorescein [DCFH; fluorescent reactive oxygen species (ROS) indicator] or Fluo-4-acetoxymethyl ester (Fluo-4-AM; fluorescent calcium indicator). When TMRE-loaded myocytes were laser illuminated, the DCFH and Fluo-4 fluorescence increased, and TMRE fluorescence decreased. These effects were significantly inhibited by NS1619 and Dia. We therefore conclude that IPT may protect the heart through activation of mitoK(ATP) and mitoK(Ca) channels, and that opening of these channels at the onset of reoxygenation protects the heart from reoxygenation injury, most likely by reducing excess generation of ROS and the resultant Ca(2+) overload.

[Sequential changes in inflammatory and stress responses during 24-hour running].

Running for an extended period of time can cause severe stress on the body, subsequently damaging skeletal muscle and resulting in changes in blood components. However, few reports have examined vital responses during and after running. This study analyzed inflammatory responses during and after running and changes in stress responses as determined by serial changes in blood components. Venous blood was obtained before starting, 6 h after starting, 12 h after starting, and immediately after finishing 24 h of continuous running. Samples were analyzed for high-sensitivity C-reactive protein (hsCRP), pentraxin 3 (ptx3), white blood cells (WBC), myoglobin, creatine kinase (CK), and hormones. Diet and physical activity were standardized 24 h before and after running. Subjects comprised 16 men who agreed to participate in experimental running on November 8 and 9, 2008, at Tokyo Gakugei University. Mean running distance was 151.32 +/- 32.1 km (range, 83.6-210.0 km) in 24 h. A significant increase in hsCRP was seen from 12 h after starting to completion. Compared to hsCRP, ptx3 gradually increased from before starting to after completion, showing a significant difference between pre and post-run ptx3 levels. WBC count increased significantly until 6 h after starting. Neutrophils in leukocytosis increased significantly during the first 6 h. Eosinophils decreased significantly over the course of the 24 h. Cortisol increased, and testosterone decreased significantly from 6 h after starting. Dehydroepiandrosterone sulfate (DHEA-S), myoglobin, and CK increased over the course of the 24 h. Reactive oxygen metabolites (d-ROMs) changed within the normal range though there was a significant decrease, and biological anti-oxidant potential (BAP) stabilized. Active natural killer cells decreased significantly after 24 h running. Biopyrrin (BPn) increased significantly. Changes in stress oxide were small both during and after running, and adaptation for antioxidation was good. DHEAS, a biomarker of aging, was found to increase over the course of the 24 h, suggesting that controlling decreases in DHEA-S may be possible using exercise, particularly in males. The key finding was that DHEA S levels tended to increase with continuous aerobic exercise.

Chronic magnesium deficiency decreases tolerance to hypoxia/reoxygenation injury in mouse heart.

AIMS: Magnesium (Mg) deficiency has been reported to be associated with the development of the metabolic syndrome, cardiovascular diseases, and sudden death. We examined the influence of chronic Mg deficiency on cardiac tolerance to hypoxia/reoxygenation injury. MAIN METHODS: Mice were fed an Mg-deficient diet for 4 weeks, and then their hearts were excised for Langendorff perfusion experiments. The levels of total Mg in the blood and heart were quantified by atomic absorption spectrometry. KEY FINDINGS: In Mg-deficient mice, the Mg concentration in whole blood was markedly decreased; however, that in the heart remained unchanged. When the hearts of control mice were exposed to hypoxia/reoxygenation, removal of extracellular Mg from a normal Krebs solution containing 1.2 mM Mg resulted in a significant decrease in the recovery of the tension-rate product (TRP) upon reoxygenation. In Mg-deficient mice, the recovery of TRP in the heart was reduced significantly in the absence of extracellular Mg compared to that in controls. The addition of Mg to the perfusate did not improve TRP recovery. During hypoxia/reoxygenation, cardiac damage evaluated by myocardial aspartate amino transferase (AST) release was greater in hearts of Mg-deficient mice than in that of control mice. SIGNIFICANCE: These results indicate that chronic Mg deficiency causes severe hypomagnesemia and a decrease in cardiac tolerance to hypoxia, without changing the intracellular Mg content. The decreased tolerance to hypoxia was not affected by the presence or absence of extracellular Mg, suggesting that some intracellular metabolic abnormalities develop in the cardiac myocytes of Mg-deficient mice.

Inhibition of connexin43 dephosphorylation is involved in protective effects of diltiazem on cardiac function during hypoxic injury.

BACKGROUND: Connexin43 (Cx43), a gap junction protein, mediates cell-cell communication via electrical and chemical coupling. Ischemic stress of the cardiac muscle interrupts intercellular communication by changing the distribution and phosphorylation status of Cx43. This may be a factor contributing to reentrant arrhythmia. The calcium channel blocker diltiazem is known for its protective and anti-arrhythmogenic effect in ischemic heart disease. In this study, we assess the effect of diltiazem pretreatment upon ischemia-induced phosphorylation change of Cx43. METHODS: Langendorff preparations of isolated Wistar rat hearts were performed. After stabilization, hearts were treated with (D+) or without diltiazem (D⁻), then subjected to hypoxia-reoxygenation. After perfusion, the left ventricle was prepared for immunocytochemistry and immunoblot analysis. RESULTS: During perfusion, left ventricular function was better in the D+ group than the D⁻ group. Immunostaining of the heart indicated that dephosphorylated Cx43 (dpCx43) signal was increased after hypoxic perfusion, and this finding was confirmed by immunoblot data. The quantitative area analysis of dpCx43 using the immunohistochemical approach showed that the dpCx43-positive area was enlarged, as the hypoxic perfusion time was longer, and it was reduced by pretreatment of diltiazem. There was a negative correlation between the dpCx43 area and %RPP (rate-pressure product), calculated by heart rate and contraction force. CONCLUSIONS: Pretreatment of diltiazem could protect the heart against hypoxia-reoxygenation injury by attenuation of dephosphorylation of Cx43. The anti-arrhythmic mechanism of diltiazem may include the preservation of phosphorylation status of Cx43 after hypoxia-reoxygenation injury.

Intracellular magnesium and tolerance against hypoxia in immature rat heart.

BACKGROUND: Neonatal hearts show greater resistance to hypoxia than adult hearts do, but the mechanism is unclear. In immature rat hearts, we examined the association between high tolerance for hypoxia and the kinetics of magnesium (Mg), which has myocardial protective effects in adult hearts. METHODS: The hearts of 1-, 2-, 3-, and 10-week-old rats were Langendorff perfused and subjected to 45 min hypoxia and 30 min reoxygenation. The myocardial Mg content was measured by atomic absorption spectrophotometry. RESULTS: In 1-week-old rat hearts, the tension-rate product recovered more immediately with reoxygenation than in the other groups, and aspartate aminotransferase release did not increase throughout the experiment. In 10-week-old rat hearts, total tissue Mg content decreased significantly with reoxygenation (607.0 ± 22.9 µg/g dry weight) from its control level (793.2 ± 16.7 µg/g dry weight). However, in neonates, the total tissue Mg did not decrease with reoxygenation. CONCLUSIONS: The high resistance against hypoxia-reoxygenation injury in neonatal rat hearts is caused, at least in part, by a high ability to maintain myocardial Mg.

Sevoflurane and nitrous oxide exert cardioprotective effects against hypoxia-reoxygenation injury in the isolated rat heart.

It is unclear whether nitrous oxide (N(2)O) has a protective effect on cardiac function in vitro. In addition, little is known about the cardioprotective effect of anesthesia administered during hypoxia or ischemia. We therefore studied the cardioprotective effects of N(2)O and sevoflurane administered before or during hypoxia in isolated rat hearts. Rat hearts were excised and perfused using the Langendorff technique. For hypoxia-reoxygenation, hearts were made hypoxic (95% N(2), 5% CO(2)) for 45 min and then reoxygenated (95% O(2), 5% CO(2)) for 40 min (control: CT group). Preconditioning was achieved through three cycles of application of 4% sevoflurane (sevo-pre group) or 50% N(2)O (N(2)O-pre group) for 5 min with 5-min washouts in between. Hypoxic conditions were achieved by administering the 4% sevoflurane (sevo-hypo group) or 50% N(2)O (N(2)O-hypo group) during the 45-min hypoxic period. L-type calcium channel currents (I(Ca,L)) were recorded on rabbit myocytes. (1) Both 4% sevoflurane and 50% N(2)O significantly reduced left ventricular developed pressure (LVDP). Sevoflurane also increased left ventricular end-diastolic pressure, though N(2)O did not. (2) The recoveries of LVDP and pressure-rate product (PRP) after hypoxia-reoxygenation were better in the sevo-pre group than in the CT or N(2)O-pre group. (3) Application of either sevoflurane or N(2)O during hypoxia improved recovery of LVDP and PRP, and GOT release was significantly lower than in the CT group. (4) Sevoflurane and N(2)O reduced I(Ca,L) to similar extents. Although sevoflurane administered before or during hypoxia exerts a cardioprotective effect, while N(2)O shows a cardioprotective effect only when administered during hypoxia.

Cholesterol depletion modulates basal L-type Ca2+ current and abolishes its -adrenergic enhancement in ventricular myocytes.

Cholesterol is a primary constituent of the plasmalemma, including the lipid rafts/caveolae, where various G protein-coupled receptors colocalize with signaling proteins and channels. By manipulating cholesterol in rabbit and rat ventricular myocytes using methyl-beta-cyclodextrin (MbetaCD), we studied the role of cholesterol in the modulation of L-type Ca(2+) currents (I(Ca,L)). MbetaCD was mainly dialyzed from BAPTA-containing pipette solution during whole cell clamp. In rabbit myocytes dialyzed with 30 mM MbetaCD for 10 min, a positive shift in membrane potential at half-maximal activation (V(0.5)) from -8 to -2 mV developed and was associated with an increase in current density at positive potentials (42% at +20 mV vs. time-matched controls). Isoproterenol (ISO) increased I(Ca,L) approximately threefold and caused a negative shift in V(0.5) in control cells, but it did not increase I(Ca,L) in MbetaCD-treated myocytes, nor did it shift V(0.5). The effect of MbetaCD (10 or 30 mM) was concentration dependent: 30 mM MbetaCD suppressed the ISO-induced increase in I(Ca,L) more effectively than 10 mM MbetaCD. MbetaCD dialysis also abolished the increase in I(Ca,L) elicited by forskolin or dibutyryl cAMP, but not that elicited by (-)BAY K 8644. External application of MbetaCD-cholesterol complex to rat myocytes attenuated the MbetaCD-mediated inhibition of the ISO-induced increase of I(Ca,L). Biochemical analysis confirmed that the myocytes' cholesterol content was diminished by MbetaCD and increased by MbetaCD-cholesterol complex. Cholesterol thus appears to contribute to the regulation of basal I(Ca,L) and beta-adrenergic cAMP/PKA-mediated increases in I(Ca,L). We suggest that cholesterol affects the structural coupling between L-type Ca(2+) channels and adjacent regulatory proteins.

[Effects of nitrous oxide and isoflurane on the L-type calcium current of rabbit ventricular myocytes and their modulation by beta-adrenoceptor stimulation].

BACKGROUND: We compared the effects of nitrous oxide (N2O) plus isoflurane with equianesthetic isoflurane alone on the L-type calcium current (I(Ca,L)), and also investigated their modulation of beta-adrenoceptor stimulation. METHODS: I(Ca,L) was recorded from enzymatically isolated rabbit ventricular myocytes using the whole-cell patch clamp technique. Ventricular myocytes were exposed to prepluses of -40 mV from a holding potential of -80 mV and then to +50 mV in 10 mV increments and thereafter the depolarization pulses that acquire peak currents were applied every 10 seconds. The changes in I(Ca,L) were measured in exposure to experimental gases of 1 MAC:1) 0.5% isoflurane and N2O:O2 (2:1) (I-N20) and 2) 1.15% isoflurane and N2:O2,(2:1) (I-N2). RESULTS: I-N2O and I-N2 depressed the peak I(Ca,L) by 15.6 +/- 9.2 and 14.6 +/- 8.1%, respectively. In the presence of 1 microM isoproterenol or 10 microM forskolin, the depression by I-N20 was significantly suppressed, but not by I-N2. CONCLUSIONS: The results show that I-N2O and I-N2 depressed I(Ca,L) to a similar degree without beta-adrenoceptor stimulation. The depression by I-N2O, however, was modulated by beta-adrenoceptor stimulation. Beta-adrenoceptor stimulation was thus found to modulate the effect of N2O combined with isoflurane rather than equianesthetic isoflurane alone.

Alterations of phosphorylation state of connexin 43 during hypoxia and reoxygenation are associated with cardiac function.

Gap junctions formed by connexins mediate cell-cell communication by electrical and chemical coupling. Recently, it has been shown that alterations in the phosphorylation state of the connexins result in functional alteration of cell-cell communication through gap junctions. Therefore, we focused on the association of alterations of phosphorylation state of connexin 43 (Cx43) with cardiac function in vivo. Rat hearts were transferred to Langendorff apparatus and submitted to hypoxia and then reoxygenated. In the control heart, Cx43 was phosphorylated and located at the intercalated disk. When the hearts were subjected to hypoxia, Cx43 at gap junctions was dephosphorylated and changed its localization to the entire plasma membrane. The area of cardiomyocytes stained with anti-phosphorylated Cx43 antibody was decreased in a time-dependent manner. Immunoblot data supported the decrease of phosphorylated Cx43 during hypoxia. ZO-1 did not change its localization at the intercalated disk during the hypoxic period. We also found that the area occupied by dephosphorylated Cx43 was correlated with the decrease of percent of rate-pressure product. These data indicate that dephosphorylation and redistribution of Cx43 is an early sign of cardiac injury after hypoxia. Detection of dephosphorylated Cx43 may serve as a diagnostic tool for examining ischemic heart disease.

Protective effects of ischemic postconditioning against hypoxia-reoxygenation injury and hydrogen peroxide-induced damage in isolated rat hearts.

OBJECTIVE: Ischemic preconditioning (PR) protects hearts from ischemia-reperfusion injury. The purpose of the present study was to examine the protective effect of PR and postconditioning (PT) against hypoxia-reoxygenation injury and H(2)O(2)-induced damage in isolated rat hearts. METHODS AND RESULTS: Hearts from male Sprague-Dawley rats were perfused with Krebs-Henseleit solution by Langendorff methods and subjected to two protocols. In protocol A, control hearts underwent 45 min of hypoxia and 30 min of reoxygenation. Three PT cycles of 10 s of ischemia and 10 s of reperfusion after 45 min of hypoxia increased the recovery of the pressure-rate product. Three PR cycles of 3 min of ischemia and 5 min of reperfusion before hypoxia were also protective, and decreased the release of glutamic oxaloacetic transaminase. A combination of PR and PT resulted in greater protection than either alone. In protocol B, control hearts underwent perfusion with H(2)O(2) (120 muM) until the left ventricular end-diastolic pressure was elevated to 50 mmHg, and then H(2)O(2) was washed out for 30 min. Three PT cycles of 30 s of ischemia and 30 s of reperfusion before the 30 min washout increased the level of recovery of the pressure-rate product and decreased left ventricular end-diastolic pressure to baseline levels. CONCLUSIONS: The results of the present study indicate that PT protects hearts from hypoxia-reoxygenation injury and H(2)O(2)-induced damage. In addition, PR combined with PT offers more effective protection than PR or PT alone.

Mechanisms of cardioprotective effects of magnesium on hypoxia-reoxygenation-induced injury.

During cardiac ischemia or hypoxia, increased levels of extracellular Mg show cardioprotective effects. The mechanisms of high level Mg-induced cardioprotection were examined in Langendorff perfused rat hearts. In the control group (1.2 mM Mg during hypoxia), the recovery of the left ventricular developed pressure (LVDP) after 30 min of reoxygenation was 57.6+/-3.0% of the level observed before hypoxia. In the high Mg group (12 mM Mg during hypoxia), the time course of recovery was faster than in the control group; the recovery level of LVDP improved to 78.4+/-4.2%. This protective effect of high levels of Mg decreased to 69.0+/-3.6% with the application of 5-hydroxydecanoic acid (100 muM), a specific mitochondrial ATP-sensitive potassium channel (K(ATP)) blocker. In the low Ca group (0.2 mM Ca during hypoxia), the recovery of LVDP did not reach the level observed in the high Mg group (64.7+/-5.9%), but with application of diazoxide, a specific mitochondrial K(ATP) channel opener, the LVDP recovery improved to 81.8+/-11.1%, similar to the level observed in the high Mg group. These results suggest that cardioprotective effects of high levels of extracellular Mg during hypoxia occur not only due to energy conservation and/or by intracellular prevention of Ca(2+) over-load, but also by opening of the mitochondrial K(ATP) channel.

Lysophosphatidylcholine-induced myocardial damage is inhibited by pretreatment with poloxamer 188 in isolated rat heart.

Lysophosphatidylcholine (LPC) accumulates in myocardial tissues and coronary sinus during ischemia, and plays important role in the development of ischemia-reperfusion injury and ischemic ventricular arrhythmia. The aim of this study was to examine whether pretreatment of poloxamer 188 (P-188), a nonionic and non-toxic surfactant, can prevent the cardiac dysfunction induced by exogenous LPC perfusion in Langendorff perfused rat heart model. LPC (6 microM) significantly (p < 0.05) decreased heart rate (HR) and left ventricular developed pressure (LVDP) from 274.3 +/- 23.2 to 175.0 +/- 42.9/min and from 115.9 +/- 11.3 to 26.7 +/- 7.1 mmHg, respectively. The LPC-induced reduction of HR and LVDP did not recover by washout of LPC. Pretreatment with P-188 (1 mM for 30 min) inhibited completely the LPC-induced decreases of HR and LVDP. The pretreatment with P-188 also prevented the LPC-induced increases of left ventricular end-diastolic pressure (LVEDP) and GOT release, significantly (p < 0.05). The coronary perfusion pressure (CPP) rose (p < 0.01) by the LPC perfusion from 71.9 +/- 5.3 to 121.9 +/- 13.0 mmHg, significantly, but pretreatment of P-188 did not affect the LPC-induced vasoconstriction. Our results suggest that exogenous LPC causes irreversible cardiac injury by the sarcolemmal membrane disruption followed by Ca overload, and this LPC-induced cardiac injury, probably, can be prevented by the pretreatment with poloxamer 188.