Phosphorylation of myocardial eNOS is altered in patients suffering from type 2 diabetes

The present study investigated whether endothelial nitric oxide synthase (eNOS) activation may be dysregulated in cardiac tissue of patients suffering from type 2 diabetes (T2D). We performed immunohistochemical measurements of translocated eNOS activation as well as eNOS phosphorylation at Ser1177, Thr495, Ser 635, Ser114, and of the protein kinase B (Akt) in isolated right atrial trabeculae of patients undergoing cardiac bypass or valve surgery with (n = 12, 68.1 ± 2.5 yr) and without T2D (n = 12, 64.7 ± 2.7 yr). In addition, we investigated oxidative (8-isoprostane) and nitrosative stress markers (nitrotyrosine) as well as the effect of pharmacological stimulation of angiotensin (AT)-receptors on eNOS-phosphorylation. Translocation-dependent eNOS activation was similar in both groups. The same holds true for eNOS phosphorylation at Ser114. eNOS phosphorylation at Ser635 was significantly increased, whereas eNOS phosphorylation of Ser1177 was significantly decreased in the diabetic group paralleled by a decrease in phosphorylation of Akt and Thr495. These alterations were accompanied by a significant decrease in nitrotyrosine. After application of angiotensin II (10 μM, 2 min) for investigation of the AT-receptor-dependent eNOS stimulation, we did not find differences between the increases in eNOS Ser1177-phosphorylation in the nondiabetic (+39.7 ± 23.5%) and in the diabetic group (32.22 ± 11.45%). A simultaneous increase in Akt phosphorylation could not be observed. The present study indicates that T2D goes along with a decrease in eNOS phosphorylation at Ser1177 under basal conditions in cardiac tissue. Whether this may be attributed to the insulin resistance of cardiac muscle has to be further investigated. Receptor-stimulated eNOS activation still works at least for angiotensin II-dependent eNOS activation.