Liu X, Takeda N, Dhalla N S
Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Metabolism. 1997 Jan;46(1):71-5. doi: 10.1016/s0026-0495(97)90171-2.
The regulatory myosin light chain (MLC) is phosphorylated in cardiac muscle by Ca2+/calmodulin-dependent MLC kinase (MLCK) and is considered to play a modulatory role in the activation of myofibrillar adenosine triphosphatase (ATPase) and the process of force generation. Since the depression in cardiac contractile function in chronic diabetes is associated with a decrease in myofibrillar ATPase activity, we investigated changes in MLC phosphorylation in diabetic heart. Rats were made diabetic by injecting streptozotocin (65 mg/kg intravenously), and the hearts were removed 8 weeks later; some 6-week diabetic animals were injected with insulin (3 U/d) for 2 weeks. Changes in the relative MLC and MLCK protein contents were measured by electrophoresis and immunoblot assay, whereas phosphorylated and unphosphorylated MLCs were separated on 10% acrylamide/urea gel and identified by Western blot. MLC and MLCK contents were decreased markedly (40% to 45%) and MLC phosphorylation was decreased significantly (30% to 45%) in the diabetic rat heart homogenate in comparison to control values. The changes in MLC and MLCK content in diabetic heart were partially reversible, whereas changes in MLC phosphorylation were normalized upon treatment with insulin. These results suggest that decreased protein contents of MLC and MLCK and phosphorylation of MLC may contribute to the depression of cardiac myofibriliar ATPase activity and heart dysfunction in diabetic cardiomyopathy.
调节性肌球蛋白轻链（MLC）在心肌中被Ca2+/钙调蛋白依赖性肌球蛋白轻链激酶（MLCK）磷酸化，并被认为在肌原纤维三磷酸腺苷酶（ATPase）的激活和力产生过程中起调节作用。由于慢性糖尿病中心脏收缩功能的降低与肌原纤维ATPase活性的降低有关，我们研究了糖尿病心脏中MLC磷酸化的变化。通过静脉注射链脲佐菌素（65 mg/kg）使大鼠患糖尿病，8周后取出心脏；一些6周龄的糖尿病动物注射胰岛素（3 U/d），持续2周。通过电泳和免疫印迹测定法测量相对MLC和MLCK蛋白含量的变化，而磷酸化和未磷酸化的MLC在10%丙烯酰胺/尿素凝胶上分离，并通过蛋白质印迹法鉴定。与对照值相比，糖尿病大鼠心脏匀浆中MLC和MLCK含量显著降低（40%至45%），MLC磷酸化显著降低（30%至45%）。糖尿病心脏中MLC和MLCK含量的变化部分可逆，而MLC磷酸化的变化在用胰岛素治疗后恢复正常。这些结果表明，MLC和MLCK蛋白含量的降低以及MLC的磷酸化可能导致糖尿病性心肌病中心肌肌原纤维ATPase活性降低和心脏功能障碍。
