Increased expression of Galphaq protein in the heart of streptozotocin-induced diabetic rats.

Heart disease is one of the major cause of death in diabetic patients, but the pathogenesis of diabetic cardio-myopathy remains unclear. In this experiment, to assess the significance of G protein signaling pathways in the pathogenesis of diabetic cardiomyopathy, we analyzed the expression of G proteins and the activities of second messenger dependent protein kinases: cAMP-dependent protein kinase (PKA), DAG-mediated protein kinase C (PKC), and calmodulin dependent protein kinase II (CaM kinase II) in the streptozotocin induced diabetic rat heart. The expression of Galphaq was increased by slightly over 10% (P<0.05) in diabetic rat heart, while Galphas, Galphai, and Gbeta remained unchanged. The PKA activity in the heart did not change significantly but increased by 27% (P<0.01) in the liver. Insulin treatment did not restore the increased activity in the liver. Total PKC activity in the heart was increased by 56% (P<0.01), and insulin treatment did not restore such increase. The CaM kinase II activity in the heart remained at the same level but was slightly increased in the liver (14% increase, P<0.05). These findings of increased expression of Galphaq in the streptozotocin-diabetic rat heart that are reflected by the increased level of PKC activity and insensitivity to insulin demonstrate that alteration of Galphaq may underlie, at least partly, the cardiac dysfunction that is associated with diabetes.