Correlation between myocardial dysfunction and changes in myosin isoenzymes in diabetic rat hearts

Subclinical Left Ventricular Longitudinal and Radial Systolic Dysfunction in Children and Adolescents with Type 1 Diabetes Mellitus

INTRODUCTION

There are few studies of subclinical systolic dysfunctions in children and adolescents with type 1 diabetes mellitus (DM), and so the available data are limited. The aim of this study was to determine early echocardiographic signs of LV systolic dysfunction in children and adolescents with type 1 DM using two-dimensional speckle tracking echocardiography (2DSTE).

MATERIAL AND METHODS

The study included 84 children and adolescents with type 1 DM and 32 sex-, age-, and body mass index-matched healthy subjects. The LV functions were assessed using conventional echocardiography, tissue Doppler imaging, and 2DSTE.

RESULTS

The results showed LV diastolic dysfunction as reflected by significantly increased A-wave velocity, decreased E/A ratio, and increased early filling deceleration time in the patients with diabetes (P = 0.02, P = 0.029, and P = 0.04; respectively). Compared with the control group, patients with diabetes showed significantly lower values for longitudinal systolic strain and strain rate in most segments of the LV; for radial strain values of the LV; for lateral circumferential strain and posterior and anterolateral circumferential strain rate of the LV; and for global longitudinal and radial strain of the LV. Global longitudinal and radial strain values of the LV were significantly lower among patients with poor glycemic control than in the control group.

CONCLUSION

In addition to diastolic dysfunction, LV longitudinal and radial function was found to be impaired in asymptomatic children and adolescents with type 1 DM who have normal LV ejection fraction by 2DSTE. Glycemic control may be the main risk factor for alteration of myocardial function.

Myosin heads are displaced from actin filaments in the in situ beating rat heart in early diabetes

Diabetes is independently associated with a specific cardiomyopathy, characterized by impaired cardiac muscle relaxation and force development. Using synchrotron radiation small-angle x-ray scattering, this study investigated in the in situ heart and in real-time whether changes in cross-bridge disposition and myosin interfilament spacing underlie the early development of diabetic cardiomyopathy. Experiments were conducted using anesthetized Sprague-Dawley rats 3 weeks after treatment with either vehicle (control) or streptozotocin (diabetic). Diffraction patterns were recorded during baseline and dobutamine infusions simultaneous with ventricular pressure-volumetry. From these diffraction patterns myosin mass transfer to actin filaments was assessed as the change in intensity ratio (I(1,0)/I(1,1)). In diabetic hearts cross-bridge disposition was most notably abnormal in the diastolic phase (p < 0.05) and to a lesser extent the systolic phase (p < 0.05). In diabetic rats only, there was a transmural gradient of contractile depression. Elevated diabetic end-diastolic intensity ratios were correlated with the suppression of diastolic function (p < 0.05). Furthermore, the expected increase in myosin head transfer by dobutamine was significantly blunted in diabetic animals (p < 0.05). Interfilament spacing did not differ between groups. We reveal that impaired cross-bridge disposition and radial transfer may thus underlie the early decline in ventricular function observed in diabetic cardiomyopathy.

Changes in crossbridge mechanical properties in diabetic rat cardiomyopathy

Diabetes mellitus is associated with an increased risk of heart failure, resulting from a specific cardiomyopathy independent of coronary atherosclerosis. It is not yet established whether altered myocardial function is related to changes in molecular mechanics of myosin. Accordingly, we investigated the total number, single force and kinetics of myosin crossbridges (CB) in a rat model of streptozotocin-induced diabetic cardiomyopathy. Experiments were conducted on left ventricular papillary muscles from male diabetic (D) Wistar (n = 16) and age-matched control (C) rats (n = 15). Mechanical indices including the maximum unloaded shortening velocity V(max) and the maximum total isometric tension normalized per cross-sectional area TF(max) were determined. Using A. F. Huxley's equations, we calculated the total cycling CB number per mm(2) Psi, the elementary force per single CB Pi, the maximum values of the rate constant for CB attachment f(1) and detachment g(1) and g(2), and the turnover rate of myosin ATPase per site k(cat). The D rats exhibited a 25% decrease in TF(max) and a 34% decrease in V(max) as compared to C. This contractile dysfunction was associated with a significant reduction in Psi (9.0 +/- 1.6 in D versus 11.4 +/- 1.9 10(9)mm(-2) in C, P < 0.001) without significant change in Pi (6.1 +/- 0.8 in D versus 6.3 +/- 0.9 pN in C, NS). In the 2 groups, TF(max) correlated positively with Psi (r = 0.76, P < 0.001 and r = 0.64, P < 0.01, in D and C respectively) but no relationship was found between TF(max) and Pi. As compared to C, D showed lower values of f(1), g(1) and g(2), and a slower turnover rate of myosin ATPase. Thus, present data suggested that the cardiac contractile impairment observed in streptozotocin-induced diabetic rat cardiomyopathy was mainly related to a decrease in active CB total number and CB kinetics alterations without significant change in CB single force.