Slecht functioneren van het hart in geval van diabetes. Rol van de Ca-homeostase
11 / 1995 - onbekend
Morbidity and death in patients with diabetes mellitus (DM) are largely caused by cardiovascular abnormalities, especially ischemic heart diseases and heart failure. Coronary sclerosis and autonomic neuropathy contribute to failure of heart function but apart from this a "diabetic cardiomyopathy" exists of which the cause has not been elucidated. It is unknown whether the stimuli which lie at the base of the diminished rates of contraction and relaxation are derived from vascular disorders caused by the diabetic milieu (glucose, insulin), from abnormalities of heart muscle or from a combination of both. Support for a role of vascular changes in the process of diabetic cardiac dysfunction is derived from the close correlation between (early) microangiopathy, marked by endothelial dysfunction with decreased NO-production and endotheline production, and heart failure. A gradual decrease in the control of calcium homeostasis, caused by diminished Ca-transport activity of the sarcoplasmic reticulum (SR) and of the plasma membrane in addition to alterations in the composition of the contractile proteins, are leading factors in the process of heart failure. The mechanisms which lie at the base of these alterations and their time course are insufficiently known. Neither it is known whether these changes are homogeneously distributed in heart muscle. The central question in this project is therefore which mechanisms are responsible for the disturbed Ca-homeostasis and changes in isoform composition of the contractile proteins in diabetic hearts. Candidates for a direct influence on the myocyte are: (I) typical diabetic factors like glucose and insulin; (II) the nitric oxide [NO]/endotheline balance, e.g. the role of the vascular bed. To answer these questions diabetic animal models will be used like streptozotocine (STZ) induced diabetes in neonatal and adult rats combined or not with hypertension and the obese Zucker rat, but also in vitro models like neonatal and adult myocytes, endothelial cells or co-cultures of both cell types. To investigate (I) small heart preparations (trabeculae) will be used to follow the mechanical changes that occur in the period (2-8 weeks) after STZ treatment and compared with changes in calcium transients during the contraction-relaxation cycle. These measurements will be completed by SRCa-ATPase (SERCA2) and myosin-ATPase analyses with immunochemical and molecular biological techniques, such as 'Northern' analysis 'nuclear run on' assay. By eliminating the paracrine influence (NO, endotheline) of the cardiac vascular bed with a short term detergent treatment it is possible to study the role of NO/endotheline in diabetic cardiomyopathy (II). The parallel studies with adult and neonatal myocytes serve to develop an in vitro diabetic model which makes accessible 1. the systematic analysis of the effects of specific changes in the 'diabetic milieu' on the myocyte and 2. the implementation of advanced molecular biological techniques such as transient expression assays for regulation studies of promoter activity of SERCA2, Na/Ca exchanger, myosin isoforms in the presence of 'diabetic' factors. The development of an in vitro system of endothelial cells cultured in a 'diabetic' milieu serves to increase our knowledge of signal/transduction routes and activities which lead to changes in endotheline/NO production which in turn influence microcirculation and contractility of the heart.