Effect of Streptozotocin-Induced Type 1 Diabetes Mellitus on Contraction, Calcium Transient, and Cation Contents in the Isolated Rat Heart (original) (raw)
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Hamdan Medical Journal
IntroductIon Diabetes mellitus (DM) is a global health problem. According to the International Diabetes Federation, 424.9 million people suffered from DM in 2017 and this number is expected to rise to 628.6 million by 2045 (http://www.diabetesatlas.org/resources/2017-atlas.html). Although DM can affect every organ in the body, cardiovascular disease is a major cause of death and disability in people with diabetes. [1-3] Diabetic patients frequently suffer from systolic and diastolic dysfunction. [4-6] The streptozotocin (STZ)-induced diabetic rat is a widely used experimental model of DM. STZ causes damage to the pancreatic β-cells, which in turn leads to a reduction in insulin synthesis and release and a consequent rise in blood glucose. [7,8] Abnormalities in a variety of haemodynamic indices including stroke volume, ejection fraction, cardiac output, rate of pressure development and relaxation have been widely demonstrated in the STZ-induced diabetic heart. [9-12] At the level of the individual ventricular myocyte, many studies have demonstrated prolonged time course of contraction and relaxation [13,14] and either Introduction: Diabetes mellitus (DM) is a global health problem. According to the International Diabetes Federation, 424.9 million people suffered from DM in 2017 and this number is expected to rise to 628.6 million by 2045. Although diabetes can affect every organ in the body, cardiovascular disease is a major cause of death and disability in people with diabetes. Diabetic patients frequently suffer from systolic and diastolic dysfunction. Within the ventricles, the electromechanical properties of cardiac myocytes vary transmurally. Aims and Objectives: The aim of this study was to investigate contraction and Ca 2+ transport in epicardial (EPI) and endocardial (ENDO) myocytes from the left ventricle in the streptozotocin (STZ)-induced diabetic rat heart. Materials and Methods: Experiments were performed 5-6 months after STZ treatment. Ventricular myocytes were isolated by enzymic and mechanical dispersal techniques from EPI and ENDO regions of the left ventricle. Contraction and free intracellular Ca 2+ concentration [Ca 2+ ]i were measured by video edge detection and fluorescence photometry techniques, respectively. Results: Myocyte length and calculated surface area were smaller in EPI-STZ compared to EPI-CON. Time to peak (TPK) shortening was prolonged in EPI-STZ compared to EPI-CON and in ENDO-STZ compared to ENDO-CON myocytes. Time to half (THALF) relaxation of shortening was prolonged in EPI-STZ compared to EPI-CON. TPK Ca 2+ transient was prolonged in EPI-STZ compared to EPI-CON, ENDO-STZ compared to ENDO-CON, ENDO-STZ compared to EPI-STZ and in ENDO-CON compared to EPI-CON myocytes. THALF decay of the Ca 2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. Fractional release of Ca 2+ was increased in ENDO-STZ compared to ENDO-CON and in ENDO-STZ compared to EPI-STZ. Recovery of the Ca 2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. Conclusion: In conclusion the kinetics of contraction and Ca 2+ transient and fractional release of Ca 2+ from the sarcoplasmic reticulum are altered to different extents in EPI and ENDO myocytes from STZ-induced diabetic rat.
Mechanisms that may be involved in calcium tolerance of the diabetic heart
The Cellular Basis of Cardiovascular Function in Health and Disease, 1997
In diabetes the hearts exhibit impaired membrane functions, but also increased tolerance to Ca 2+ (iCaT) However, neither the true meaning nor the molecular mechanisms of these changes are fully understood. The present study is devoted to elucidation of molecular alterations, particularly those induced by non-enzymatic glycation of proteins, that may be responsible for iCaT of the rat hearts in the stage of fully developed, but still compensated diabetic cardiomyopathy (DH). Insulin-dependent diabetes (DIA) was induced by a single i.v. dose of streptozotocin (45 mg.kg -1 ). Beginning with the subsequent day, animals obtained 6 U insulin daily. Glucose, triglycerides, cholesterol and glycohemoglobin were investigated in blood. ATPase activities, the kinetics of activation of (Na,K)-ATPase by Na + and K + , further the fluorescence anisotropy of diphenyl-hexatriene as well as the order parameters of membranes in isolated heart sarcolemma (SL) were also investigated. In addition, the degree of glycation and glycation-related potency for radical generation in SL proteins were determined by investigating their fructosamine content. In order to study calcium tolerance of DH in a 'transparent' model, hearts were subjected to calcium paradox (Ca-Pa, 3 min of Ca 2+ depletion; 10 min of Ca 2+ repletion). In this model of Ca 2+ -overload, Ca 2+ ions enter the cardiac cells in a way that is not mediated by receptors. Results revealed that more than 83% of the isolated perfused DH recovered, while the non-DIA control hearts all failed after Ca-Pa. DH exhibited well preserved SL ATPase activities and kinetics of (Na,K)-ATPase activation by Na + , even after the Ca-Pa. This was considered as a reason for their iCaT. Pretreatment and administration of resorcylidene aminoguanidine (RAG 4 or 8 mg.kg -1 ) during the disease prevented partially the pathobiochemical effects of DIA-induced glycation of SL proteins. DIA-induced perturbations in anisotropy and order parameters of SL were completely prevented by administration of RAG (4 mg.kg -1 ). Although, the latter treatment exerted little influence on the (Na,K)-ATPase activity, it decreased the calcium tolerance of the DH. Results are supporting our hypothesis that the glycation-induced enhancement in free radical formation and protein crosslinking in SL may participate in adaptive mechanisms that may be also considered as 'positive' and are responsible for iCaT of the DH. (Mol Cell Biochem 176: 191-198, 1997)
Dyssynchronous (non-uniform) Ca2+ release in myocytes from streptozotocin-induced diabetic rats
Journal of Molecular and Cellular Cardiology, 2007
Using biochemical/pharmacological approaches, we previously showed that type 2 ryanodine receptors (RyR2) become dysfunctional in hearts of streptozotocin-induced type 1 diabetic rats. However, the functional consequence of this observation remains incompletely understood. Here we use laser confocal microscopy to investigate whether RyR2 dysfunction during diabetes alters evoked and spontaneous Ca 2+ release from the sarcoplasmic reticulum (SR). After 7-8 weeks of diabetes, steady-state levels of RyR2 remain unchanged in hearts of male Sprague-Dawley rats, but the number of functional receptors decreased by > 37%. Interestingly, residual functional RyR2 from diabetic rat hearts exhibited increased sensitivity to Ca 2+ activation (EC 50activation decreased from 80 μM to 40 μM, peak Ca 2+ activation decreased from 425 μM to 160 μM). When field stimulated, intracellular Ca 2+ release in diabetic ventricular myocytes was dyssynchronous (non-uniform) and this was independent of L-type Ca 2+ currents. Time to peak Ca 2+ increased 3.7-fold. Diabetic myocytes also exhibited diastolic Ca 2+ release and 2-fold higher frequency of spontaneous Ca 2+ sparks, albeit at a lower amplitude. The amplitude of caffeine-releasable Ca 2+ was also lower in diabetic myocytes. RyR2 from diabetic rat hearts exhibited increased phosphorylation at Ser2809 and contained reduced levels of FKBP12.6 (calstablin2). Collectively, these data suggest that RyR2 becomes leaky during diabetes and this defect may be responsible to the reduced SR Ca 2+ load. Diastolic Ca 2+ release could also serve as a substrate for delayed after-depolarizations, contributing to the increased incidence of arrhythmias and sudden cardiac death in type 1 diabetes.
Journal of Advanced Research, 2013
The endothelium-derived hyperpolarizing factor (EDHF) response is a critical for the functioning of small blood vessels. We investigated the effect of streptozotocin-induced diabetes on the EDHF response and its possible role in the regulation of cardiac function. The vasorelaxant response to ACh-or NS309-(direct opener endothelial small-(SK Ca)-and intermediateconductance (IK Ca) calcium-activated potassium channels; main components of EDHF response) were measured in pressurized mesenteric arteries (diameter 300-350 lm). The response to 1 lM ACh was reduced in diabetes (84.8 ± 2.8% control vs 22.5 ± 5.8% diabetics; n P 8; P < 0.001). NS309 (1 lM) relaxations were also decreased in diabetic arteries (78.5 ± 8.7% control vs 32.1 ± 5.8% diabetics; n P 5; P < 0.001). SK Ca and IK Ca-mediated EDHF relaxations in response ACh or NS309 were also significantly reduced by diabetes. Ruthenium red, RuR, a blocker of TRP channels, strongly depress the response to ACh and NS309 in control and diabetic arteries. RuR decreased SK Ca and IK Ca-mediated EDHF vasodilatation in response to NS309 but not to ACh. An elevation in systolic blood pressure was observed in diabetic animals. ECG recording of control hearts showed shortening of PR interval. RuR reduced PR interval and R wave amplitude in diabetic hearts. In conclusion, the reduced EDHF-type relaxations in STZ-induced diabetes is due impairment of K Ca channels function. TRP channels possibly contribute to EDHF vasodilatation
Ca2+ blocker therapy and cardiac function in diabetes
Journal of Molecular and Cellular Cardiology, 1987
Tissue sodium accumulation has been the sole steady state cation abnormality in myocardium of a canine model with mild diabetes and prolonged action potential duration. (J. Clin. Invest. 77,382, '86). Since reduced levels of myoinositol have been associated with sodium gain in some diabetic tissues, we have examined this relationship in healthy male mongrel dogs 2 to 4 yrs of age. Alloxan was given i.v. 30mg/kg. A moderate hyperglycemic level was maintained with daily insulin. After I yr the heart was cold arrested in the anesthetized animal and analyzed for tissue electrolytes, myoinositol and sorbitol by GLC. Sodium concentration in left ventricular tissue was increased to 44.3• uM/gm wet wt in D. vs 34• in controls. Myoinositol was reduced from 1.23• uM/gm wet wt in normals to 0.59• in diabetics. Similar alterations were observed in Purkinje fasicle. That this was independent of aldose reductase activity was suggested by normal sorbitol concentrations, .32• in D and .33• in controls. Thus delivery of myoinositol to cardiac tissue was presumed to be impaired. Since normalization of myoinositol has been reported in other tissues to normalize sodium content and abnormal repolarization in diabetes, these variables may be similarly related in heart.
Molecular and Cellular Biochemistry, 2005
Administration of a single high-dose (SHD) of streptozotocin (STZ) to young adult rats causes a diabetic cardiomyopathy. Albino Oxford (AO) and Dark Agouti (DA) inbred strains of rats are susceptible to developing diabetes when administered a SHD of STZ but differ in susceptibility to multiple low-dose (MLD) STZ. We have investigated the effects of SHD and MLD-STZ on contraction and intracellular Ca 2+ , measured with fura-2, in ventricular myocytes from AO and DA rats at 18-20 weeks after treatment. Time to peak shortening was significantly prolonged in myocytes from DA rats after SHD-STZ but was not altered in DA rats after MLD-STZ or in AO rats by either MLD or SHZ-STZ treatment. Time to peak shortening in myocytes from DA control and DA rats after SHD-STZ were 88 ± 2 ms and 107 ± 4 ms, respectively. Time to half relaxation and the amplitude of myocyte shortening were not altered in AO or DA rats by either MLD or SHD-STZ treatment. Amplitude, time to peak fura-2 transient and time to half relaxation of the fura-2 transient were not significantly altered in AO or DA rats by either MLD or SHD-STZ treatment. Contractile defects reported in myocytes from SHD-STZ treated DA rats may be a consequence of altered myofilament sensitivity to Ca 2+. The hyperglycaemic effects of MLD-STZ and SHD-STZ induced diabetes was much greater in DA compared to AO rats and the effects of the hyperglycaemia on the time-course of ventricular myocyte contraction was most profound in DA rats after SHD-STZ.
Molecular and cellular …, 2004
General anaesthetics have previously been shown to have profound effects on myocardial function. Moreover, many patients suffering from diabetes mellitus are anaesthetised during surgery. This study investigated compromised functioning of cardiac myocytes from streptozotocin (STZ)-induced diabetic rats and the additive effects of halothane on these dysfunctions. Ventricular myocytes were isolated from 8 to 12 weeks STZ-treated rats. Contraction and intercellular free calcium concentration ([Ca 2+ ] i) were measured in electrically field-stimulated (1 Hz) fura-2-AM-loaded cells using a video-edge detection system and a fluorescence photometry system, respectively. L-type Ca 2+ current was measured in whole cell, voltage-clamp mode. Halothane significantly (p < 0.01) depressed the amplitude and the time course of the Ca 2+ transients in a similar manner in myocytes from control and STZ-treated rats. However, the effect of halothane on the amplitude of shortening and L-type Ca 2+ current was more pronounced in myocytes from STZ-treated animals compared to age-matched controls. Myofilament sensitivity to Ca 2+ was significantly (p < 0.01) increased in myocytes from STZ-treated rats compared to control. However, in the presence of halothane the myofilament sensitivity to Ca 2+ was significantly (p < 0.05) reduced to a greater extent in myocytes from STZ-treated rats compared to controls. In conclusion, these results show that contractility, Ca 2+ transport and myofilament sensitivity were all altered in myocytes from STZ-treated rats and these processes were further altered in the presence of halothane suggesting that hearts from STZ-induced diabetic rats are sensitive to halothane. (Mol Cell Biochem xxx: 1-11, 2004)