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Abstract   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 Ca2 regulation in myocardium of asymptomatic type 2 diabetic patients. Methods Alterations in the dynamics of the intracellular Ca2 transient and contractility were recorded in right atrial myocardium of type 2 diabetic patients and non-diabetic control tissue loaded with fura-2. In order to gain an insight into mechanisms underlying the altered Ca2 handling in diabetic myocardium levels of mRNA, protein expression and phosphorylation of key proteins in sarcoplasmic Ca2 handling were determined. Results In isolated atrial trabeculae of diabetic myocardium the rise of systolic Ca2 was significantly prolonged, but relaxation of the Ca2 transient was unaltered compared to control tissue. Accordingly, the levels of expression of mRNA and protein of the Ca2 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 Ca2 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 Ca2 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. [ABSTRACT FROM AUTHOR]

Human hibernating myocardium (HHM) is characterized by reversible contractile dysfunction during chronic ischemia. A disturbed calcium-homeostasis is a decisive factor for reduced functional capacity in heart diseases. We therefore investigated calcium-handling proteins in HHM. In 12 patients suffering from multi-vessel coronary artery disease and contractile dysfunction with indication for bypass surgery, HHM was detected preoperatively by thallium scintigraphy, radionuclide ventriculography and dobutamine echocardiography. Transmural biopsies of these regions were taken and analyzed by immunohistochemistry and electron microscopy. Furthermore, SR-calcium ATPase (SERCA2a), phospholamban (PLN), the phosphorylated forms of PLN (PLN-Ser16, PLN-Thr17) as well as sodium-calcium exchanger (NCX) and ryanodine receptor (RyR2) were investigated by RT-PCR and Western-blotting. Additionally, SERCA2a activity was measured by an enzyme-coupled assay. In all patients complete functional recovery could be documented 3 months after revascularization by repeating all preoperative investigations. In HHM maximal SERCA2a activity was significantly reduced (HHM: 424.5± 33.9, control: 609.0± 48.5 nmol ATP mg protein−1 min−1, p≰ 0.05), whereas SERCA2a protein levels were unchanged. mRNA levels (HHM: 1.36± 0.08 vs. control: 0.78± 0.04, p≰ 0.05) and protein amount (HHM:1.67± 0.14 vs. control: 1.00± 0.04, p≰ 0.05) of PLN (A1) were increased resulting in an increased PLN:SERCA2a-ratio. PLN-Ser16 (HHM: 0.60± 0.08 vs. control: 1.00± 0.11, p≰ 0.05) and PLN-Thr17 (HHM: 0.63± 0.11 vs. control: 1.00± 0.06, p≰ 0.05) phosphorylation was significantly decreased. RyR2 and NCX showed no significant alteration. In HHM a decreased activity of SERCA2a due to an impaired phosphorylation of PLN contributes to contractile dysfunction. The increase in the relative ratio of PLN/SERCA2a leads to a decreased calcium affinity of SERCA2a. [ABSTRACT FROM AUTHOR]