Defective intracellular Ca 2+ signaling contributes to cardiomyopathy in Type 1 diabetic rats (original) (raw)
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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.
FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 2002
Slowed relaxation in diabetic cardiomyopathy (CM) is partially related to diminished expression of the sarcoplasmic reticulum (SR) Ca2+-ATPase SERCA2a. To evaluate the impact of SERCA2a overexpression on SR Ca2+ handling in diabetic CM, we 1) generated transgenic rats harboring a human cytomegalovirus enhancer/chicken beta-actin promotor-controlled rat SERCA2 transgene (SERCA2-TGR), 2) characterized their SR phenotype, and 3) examined whether transgene expression may rescue SR Ca2+ transport in streptozotocin-induced diabetes. The transgene was expressed in all heart chambers. Compared to wild-type (WT) rats, a heterozygous line exhibited increased SERCA2 mRNA (1.5-fold), SERCA2 protein (+26%) and SR Ca2+ uptake (+37%). Phospholamban expression was not altered. In SERCA2-TGR, contraction amplitude (+48%) and rates of contraction (+34%) and relaxation (+35%) of isolated papillary muscles (PM) were increased (P2+ uptake and SERCA2 protein of SERCA2-TGR were 1.3-fold higher (P2+ uptake...
Diabetes, 2005
The defects identified in the mechanical activity of the hearts from type 1 diabetic animals include alteration of Ca 2؉ signaling via changes in critical processes that regulate intracellular Ca 2؉ concentration. These defects result partially from a dysfunction of cardiac ryanodine receptor calcium release channel (RyR2). The present study was designed to determine whether the properties of the Ca 2؉ sparks might provide insight into the role of RyR2 in the altered Ca 2؉ signaling in cardiomyocytes from diabetic animals when they were analyzed together with Ca 2؉ transients. Basal Ca 2؉ level as well as Ca 2؉-spark frequency of cardiomyoctes isolated from 5-week streptozotocin (STZ)induced diabetic rats significantly increased with respect to aged-matched control rats. Ca 2؉ transients exhibited significantly reduced amplitude and prolonged time courses as well as depressed Ca 2؉ loading of sarcoplasmic reticulum in diabetic rats. Spatio-temporal properties of the Ca 2؉ sparks in cardiomyocytes isolated from diabetic rats were also significantly altered to being almost parallel to the changes of Ca 2؉ transients. In addition, RyR2 from diabetic rat hearts were hyperphosphorylated and protein levels of both RyR2 and FKBP12.6 depleted. These data show that STZ-induced diabetic rat hearts exhibit altered local Ca 2؉ signaling with increased basal Ca 2؉ level.
Sarcoplasmic Ca2+ release is prolonged in nonfailing myocardium of diabetic patients
Molecular and Cellular Biochemistry, 2008
Background Asymptomatic diabetic patients have a high incidence of clinically unrecognized left ventricular dysfunction with an abnormal cardiac response to exercise. We, therefore, examined subclinical defects in the contraction-relaxation cycle and intracellular Ca 2+ regulation in myocardium of asymptomatic type 2 diabetic patients. Methods Alterations in the dynamics of the intracellular Ca 2+ transient and contractility were recorded in right atrial myocardium of type 2 diabetic patients and nondiabetic control tissue loaded with fura-2. In order to gain an insight into mechanisms underlying the altered Ca 2+ handling in diabetic myocardium levels of mRNA, protein expression and phosphorylation of key proteins in sarcoplasmic Ca 2+ handling were determined. Results In isolated atrial trabeculae of diabetic myocardium the rise of systolic Ca 2+ was significantly prolonged, but relaxation of the Ca 2+ transient was unaltered compared to control tissue. Accordingly, the levels of expression of mRNA and protein of the Ca 2+ release channel (RyR2) of the sarcoplasmic reticulum were reduced by 68 and 22%, respectively. Endogenous phosphorylation of RyR2 by protein kinases C, however, was increased by 31% in diabetic myocardium, as assessed by the back-phosphorylation technique. Levels of expression of SERCA2 and phospholamban were unaltered between both groups. Conclusions Intracellular Ca 2+ release is prolonged in non-failing myocardium of type 2 diabetic patients and this may be primarily due to a decreased expression of RyR2. This defective Ca 2+ release may represent an early stage of ventricular dysfunction in type 2 diabetes and would favor the abnormal response to exercise frequently observed in asymptomatic diabetic patients.
Calcium signaling in diabetic cardiomyocytes
Cell Calcium, 2014
Diabetes mellitus is one of the most common medical conditions. It is associated to medical complications in numerous organs and tissues, of which the heart is one of the most important and most prevalent organs affected by this disease. In fact, cardiovascular complications are the most common cause of death among diabetic patients. At the end of the 19th century, the weakness of the heart in diabetes was noted as part of the general muscular weakness that exists in that disease. However, it was only in the eighties that diabetic cardiomyopathy was recognized, which comprises structural and functional abnormalities in the myocardium in diabetic patients even in the absence of coronary artery disease or hypertension. This disorder has been associated with both type 1 and type 2 diabetes, and is characterized by earlyonset diastolic dysfunction and late-onset systolic dysfunction, in which alteration in Ca 2+ signaling is of major importance, since it controls not only contraction, but also excitability (and therefore is involved in rhythmic disorder), enzymatic activity, and gene transcription. Here we attempt to give a brief overview of Ca 2+ fluxes alteration reported on diabetes, and provide some new data on differential modulation of Ca 2+ handling alteration in males and females type 2 diabetic mice to promote further research. Due to space limitations, we apologize for those authors whose important work is not cited.
Effects of diabetes and hypertension on myocardial Na + -Ca 2+ exchange
Canadian Journal of Physiology and Pharmacology, 1999
Abnormalities in cardiac function have been extensively documented in experimental and clinical diabetes. These aberrations are well known to be exaggerated when hypertension and diabetes co-exist. The objective of the present study was to examine whether alterations in the activity of the myocardial Na + -Ca 2+ exchanger (NCX) can account for the deleterious effects of diabetes and (or) hypertension on the heart. To this aim, the following experimental groups were studied: (i) control; (ii) diabetic; (iii) hypertensive; and (iv) hypertensive-diabetic. Wistar rats served as the control group (C) while Wistar rats injected with streptozotocin (STZ, 55 mg/kg) served as the diabetic (D) group. Spontaneously hypertensive (SH) rats were used as the hypertensive group (H) while SH rats injected with STZ served as the hypertensive-diabetic (HD) group. Sarcolemma was isolated from the ventricles of the C, D, H, and HD groups and NCX activity was examined using rapid quenching techniques to study initial rates over a [Ca 2+ ] o range of 10-160 µM. The V max of NCX was lower in the D group when compared with the C group (D, 2.96 ± 0.26 vs. C, 4.0 ± 0.46 nmol·mgprot -1 ·s -1 , P < 0.05), however combined diabetes and hypertension (HD) did not affect the V max of NCX activity (HD, 3.84 ± 0.88 vs. H, 3.59 ± 0.24 nmol·mgprot -1 ·s -1 , P > 0.05). However, analysis of the K m values for Ca 2+ indicated that both the D and HD groups exhibited a significantly lower K m when compared with their respective control groups (D, 42 ± 4 vs. C, 56 ± 4 µM, P < 0.05; HD, 33 ± 7 vs. H, 51 ± 8 µM, P < 0.05). Immunoblotting using polyclonal antibodies (against canine cardiac NCX) exhibited the typical banding of 160, 120, and 70 kDa. The 120 kDa band is believed to represent the native exchanger with its post-translational modifications. Examination of the blots revealed a lower intensity of the 120 kDa band in the D group when compared with the C group, however, no significant difference in the HD group was observed. We speculate that the lower V max in the D group may be due to a reduced concentration of exchanger protein in the membrane. The absence of this defect in the HD group may be a result of compensatory mechanisms to the overall hemodynamic overload, however, this remains to be determined. The increased affinity for Ca 2+ in both the D and HD groups (determined by the lower K m values) is an interesting finding and may be due to changes in sarcolemmal lipid bilayer composition secondary to diabetes-induced hyperlipidemia.
European Journal of Endocrinology, 1996
Gøtzsche LB-H, Rosenqvist N. Grønbœk H, Flyvbjerg A, Gøtzsche O. Increased number of myocardial voltage-gated Ca2+ channels and unchanged total β-receptor number in long-term streptozotocin-diabetic rats. Eur J Endocrinol 1996;134:107–13. ISSN 0804–4643. In order to elucidate further the abnormal myocardial Ca+ metabolism in diabetes mellitus, voltage-gated Ca2+ channels and β-receptors were quantified in myocardial membranes of short- and long-term diabetic rats. Diabetes was induced by an injection of streptozotocin (STZ). Animals were killed 2, 4, 7, 90 and 200 days after STZ. A group of diabetic animals were treated with insulin for 20 days following 180 days of untreated diabetes. Diabetic animals developed low triiodothyronine syndrome. During short-term diabetes, the maximum binding capacity (MBC) for Ca+ channels was reduced by 25% at day 4 p<0.05) and the β-receptor MBC was reduced by 48% p<0.05). A normalizing tendency was observed at day 7 for both receptor types; i...
Scientific Reports
Systolic and diastolic dysfunction in diabetes have frequently been associated with abnormal calcium (Ca2+) regulation. However, there is emerging evidence that Ca2+ mishandling alone is insufficient to fully explain diabetic heart dysfunction, with focus shifting to the properties of the myofilament proteins. Our aim was to examine the effects of diabetes on myofilament Ca2+ sensitivity and Ca2+ handling in left ventricular tissues isolated from the same type 2 diabetic rat hearts. We measured the force-pCa relationship in skinned left ventricular cardiomyocytes isolated from 20-week-old type 2 diabetic and non-diabetic rats. Myofilament Ca2+ sensitivity was greater in the diabetic relative to non-diabetic cardiomyocytes, and this corresponded with lower phosphorylation of cardiac troponin I (cTnI) at ser23/24 in the diabetic left ventricular tissues. Protein expression of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), phosphorylation of phospholamban (PLB) at Ser16, and SERCA/PL...
Experimental Physiology, 2011
The association between type 2 diabetes and obesity is very strong, and cardiovascular complications are the major cause of morbidity and mortality in diabetic patients. The aim of this study was to investigate early changes in the pattern of genes encoding cardiac muscle regulatory proteins and associated changes in ventricular myocyte contraction and Ca 2+ transport in young (9-to 13-week-old) type 2 Zucker diabetic fatty (ZDF) rats. The amplitude of myocyte shortening was unaltered; however, time-to-peak shortening and time to half-relaxation of shortening were prolonged in ZDF myocytes (163 ± 5 and 127 ± 7 ms, respectively) compared with age-matched control rats (136 ± 5 and 103 ± 4 ms, respectively). The amplitude of the Ca 2+ transient was unaltered; however, time-to-peak Ca 2+ transient was prolonged in ZDF myocytes (66.9 ± 2.6 ms) compared with control myocytes (57.6 ± 2.3 ms). The L-type Ca 2+ current was reduced, and inactivation was prolonged over a range of test potentials in ZDF myocytes. At 0 mV, the density of L-type Ca 2+ current was 1.19 ± 0.28 pA pF −1 in ZDF myocytes compared with 2.42 ± 0.40 pA pF −1 in control myocytes. Sarcoplasmic reticulum Ca 2+ content, release and uptake and myofilament sensitivity to Ca 2+ were unaltered in ZDF myocytes compared with control myocytes. Expression of genes encoding various L-type Ca 2+ channel proteins (Cacna1c, Cacna1g , Cacna1h and Cacna2d1) and cardiac muscle proteins (Myh7) were upregulated, and genes encoding intracellular Ca 2+ transport regulatory proteins (Atp2a2 and Calm1) and some cardiac muscle proteins (Myh6, Myl2, Actc1, Tnni3, Tnn2, and Tnnc1) were downregulated in ZDF heart compared with control heart. A change in the expression of genes encoding myosin heavy chain and L-type Ca 2+ channel proteins might partly underlie alterations in the time course of contraction and Ca 2+ transients in ventricular myocytes from ZDF rats.
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.