Effects of halothane on contraction and intracellular calcium in ventricular myocytes from streptozotocin-induced diabetic rats

Calcium signaling in endocardial and epicardial ventricular myocytes from streptozotocin-induced diabetic rats

AIMS/INTRODUCTION

Abnormalities in Ca2+ signaling have a key role in hemodynamic dysfunction in diabetic heart. The purpose of this study was to explore the effects of streptozotocin (STZ)-induced diabetes on Ca2+ signaling in epicardial (EPI) and endocardial (ENDO) cells of the left ventricle after 5-6 months of STZ injection.

MATERIALS AND METHODS

Whole-cell patch clamp was used to measure the L-type Ca2+ channel (LTCC) and Na+ /Ca2+ exchanger currents. Fluorescence photometry techniques were used to measure intracellular free Ca2+ concentration.

RESULTS

Although the LTCC current was not significantly altered, the amplitude of Ca2+ transients increased significantly in EPI-STZ and ENDO-STZ compared with controls. Time to peak LTCC current, time to peak Ca2+ transient, time to half decay of LTCC current and time to half decay of Ca2+ transients were not significantly changed in EPI-STZ and ENDO-STZ myocytes compared with controls. The Na+ /Ca2+ exchanger current was significantly smaller in EPI-STZ and in ENDO-STZ compared with controls.

CONCLUSIONS

STZ-induced diabetes resulted in an increase in amplitude of Ca2+ transients in EPI and ENDO myocytes that was independent of the LTCC current. Such an effect can be attributed, at least in part, to the dysfunction of the Na+ /Ca2+ exchanger. Additional studies are warranted to improve our understanding of the regional impact of diabetes on Ca2+ signaling, which will facilitate the discovery of new targeted treatments for diabetic cardiomyopathy.

Improvement of cardiomyocyte function by in vivo hexarelin treatment in streptozotocin-induced diabetic rats

Diabetic cardiomyopathy is characterized by diastolic and systolic cardiac dysfunction, yet no therapeutic drug to specifically treat it. Hexarelin has been demonstrated to improve heart function in various types of cardiomyopathy via its receptor GHS-R. This experiment aims to test the effect of hexarelin on cardiomyocytes under experimental diabetes. Streptozotocin (STZ, 65 mg/kg)-induced diabetic rat model was employed with vehicle injection group as control. Daily hexarelin (100 μg/kg) treatment was performed for 2 weeks after 4-week STZ-induced diabetes. Cardiomyocytes were isolated by enzyme treatment under O2 -saturated perfusion for single-cell shortening, [Ca2+ ]i transient, and electrophysiology recordings. GHS-R expression and apoptosis-related signaling proteins Bax, Bcl-2, caspase-3 and 9, were assessed by western blot. Experimental data demonstrated a reduced cell contraction and relaxation in parallel with depressed rise and fall of [Ca2+ ]i transients in diabetic cardiomyocytes. Hexarelin reversed the changes in both contraction and [Ca2+ ]i . Action potential duration and transient outward potassium current (Ito ) density were dramatically increased in diabetic cardiomyocytes and hexarelin treatment reverse such changes. Upregulated GHS receptor (GHS-R) expression was observed in both control and diabetic groups after hexarelin treatment, which also caused antiapoptotic changes of Bax, Bcl-2, caspase-3 and 9 expression. In STZ-induced diabetic rats, hexarelin is able to improve cardiomyocyte function through recovery of Ito K+ currents, intracellular Ca2+ homeostasis and antiapoptotic signaling pathways.

Effect of isoflurane on myocardial energetic and oxidative stress in cardiac muscle from Zucker diabetic fatty rat

The effect of inhalational anesthetics on myocardial contraction and energetics in type 2 diabetes mellitus is unknown. We investigated the effect of isoflurane (ISO) on force and intracellular Ca(2+) transient (iCa), myocardial oxygen consumption (MVo(2)), and energetics/redox behavior in trabecular muscles from Zucker diabetic fatty (ZDF) rats. At baseline, force and corresponding iCa were lower in ZDF trabeculae than in controls. ISO decreased force in both groups in a dose-dependent manner. ISO did not affect iCa amplitude in controls, but ISO > 1.5% significantly reduced iCa amplitude in ZDF trabeculae. ISO-induced force depression fully recovered as a result of increased iCa when external Ca(2+) was raised in controls. However, both force and iCa remained low in ZDF muscle at elevated external Ca(2+). In controls, force, iCa, and MVo(2) increased when stimulation frequency was increased from 0.5 to 1.5 Hz. ZDF muscles, however, exhibited blunted responses in force and iCa and decreased MVo(2). Oxidative stress levels were unchanged in control muscles but increased significantly in ZDF muscles after exposure to ISO. Finally, the depressive effect of ISO was prevented by 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (Tempol) in ZDF muscles. These findings suggest that ISO dose-dependently attenuates force in control and ZDF muscles with differential effect on iCa. The mechanism of force depression by ISO in controls is mainly decreased myofilament Ca(2+) sensitivity, whereas in ZDF muscles the ISO-induced decrease in contraction is due to worsening oxidative stress, which inhibits iCa and force development.

The common anesthetic, sevoflurane, induces apoptosis in A549 lung alveolar epithelial cells

Lung alveolar epithelial cells are the first barrier exposed to volatile anesthetics, such as sevoflurane, prior to reaching the targeted neuronal cells. Previously, the effects of volatile anesthetics on lung surfactant were studied primarily with physicochemical models and there has been little experimental data from cell cultures. Therefore it was investigated whether sevoflurane induces apoptosis of A549 lung epithelial cells. A549 cells were exposed to sevoflurane via a calibrated vaporizer with a 2 l/min flow in a gas‑tight chamber at 37˚C. The concentration of sevoflurane in Dulbecco's modified Eagle's medium was detected with gas chromatography. Untreated cells and cells treated with 2 µM daunorubicin hydrochloride (DRB) were used as negative and positive controls, respectively. Apoptosis factors, including the level of ATP, apoptotic‑bodies by terminal deoxynucleotidyl transferase‑mediated dUTP nick end labeling (TUNEL) assay, DNA damage and the level of caspase 3/7 were analyzed. Cells treated with sevoflurane showed a significant reduction in ATP compared with untreated cells. Effects in the DRB group were greater than in the sevoflurane group. The difference of TUNEL staining between the sevoflurane and untreated groups was statistically significant. DNA degradation was observed in the sevoflurane and DRB groups, however this was not observed in the untreated group. The sevoflurane and DRB groups induced increased caspase 3/7 activation compared with untreated cells. These results suggest that sevoflurane induces apoptosis in A549 cells. In conclusion, 5% sevoflurane induced apoptosis of A549 lung alveolar epithelial cells, which resulted in decreased cell viability, increased apoptotic bodies, impaired DNA integrality and increased levels of caspase 3/7.

Morphology and Contractility of Cardiac Myocytes in Early Stages of Streptozotocin-Induced Diabetes Mellitus in Rats

Diabetic cardiomyopathy is the leading cause of mortality in type 1 diabetes. Thus study of cardiomyocyte morphology and function during early stages of diabetes using modern analytical methods is of critical importance. Therefore, using confocal microscopy, we determined metric parameters, volumes and contractility, with calcium transients in isolated left-ventricular myocytes at one week after induction of diabetes in rats. Myocyte volume analysis from 3D confocal scans was performed using an automated contour detection algorithm that took the actual shape of the myocytes into account. We showed a significant reduction in myocyte volume in diabetic animals. We also showed a significant reduction in length and width but not in thickness of the myocytes, which suggests disproportional reorganization of the structure of the heart tissue during short-term diabetes. From a functional point of view, we observed a significant decrease in cell shortening at a stimulation frequency of 0.5 Hz. This was accompanied by a decrease in calcium transient amplitude. Together, these data suggest that impaired calcium handling is one of the factors that contributes to the observed decrease in myocyte shortening during early stages of streptozotocin-induced diabetes in rats.

Diabetes and the heart: could the diabetic myocardium be protected by preconditioning?

Both type 1 and type 2 diabetes (insulin-dependent and non-insulin dependent diabetes, respectively) are associated with increased risk for microvascular and macrovascular complications including retinopathy, neuropathy, nephropathy and atherosclerosis. Type 2 diabetes markedly increases the risk for cardiovascular morbidity and mortality, which has major public health implications. In this review, molecular mechanisms pertaining to diabetes-induced heart pathology are addressed.

Mitochondria are involved in stress response of A549 alveolar cells to halothane toxicity

During inhalation anaesthesia lung epithelial cells are directly exposed to halogenated hydrocarbons such as halothane. Information about the effects of volatile anaesthetics on lung cells is rather limited although their noxious effect on the A549 alveolar cells has been shown recently. The present study indicated that halothane decreases cell viability, impairs DNA integrity and provokes stress-induced apoptosis in A549 cells when applied at clinically relevant concentrations. Data obtained clearly demonstrated intensive expression of anti-apoptotic Bcl-2 protein during treatment with all tested concentrations. In post-treatment periods the increased DNA injury was accompanied by reduction of Bcl-2 expression. We concluded that the in vitro effect of halothane on lung cells involved alteration in the expression of proteins of the mitochondrial apoptotic pathway.