Enhanced activity of the myocardial Na+/H+ exchanger contributes to left ventricular hypertrophy in the Goto-Kakizaki rat model of type 2 diabetes: Critical role of Akt

Abstract

Aims/hypothesis: Diabetes mellitus is a strong risk factor for the development of heart failure, and left ventricular (LV) hypertrophy has been detected in a significant proportion of diabetic patients. Because several studies have suggested that the Na+/H+ exchanger (NHE1) plays a part in the molecular mechanisms involved in cardiac hypertrophy, we investigated its activity and its role in LV myocytes from the Goto-Kakizaki (GK) rat model of type 2 diabetes. Materials and methods: Fluorometric measurements were used to assess sarcolemmal NHE1 activity in isolated myocytes. NHE1 levels and the possible molecular pathways driving and/or related to NHE1 activity were investigated in relation to the diabetic LV phenotype. Results: Enhanced NHE1 activity was associated with LV myocyte hypertrophy. This occurred in the absence of any change in NHE1 protein levels; however, activation of several molecular pathways related to NHE1 activity was demonstrated. Thus, phosphorylation of the extracellular signal-regulated protein kinase (Erk), of the protein kinase Akt (also known as protein kinase B) and of the Ca 2+/calmodulin-dependent kinase II was increased in GK LV myocytes. Intracellular Ca2+ levels were also increased. Chronic treatment (10-12 weeks) with the NHE1 inhibitor cariporide normalised NHE1 activity, decreased Cai2+ levels and reduced LV myocyte hypertrophy. Moreover, among the various activated pathways, cariporide treatment markedly reduced Akt activity only. Conclusions/interpretation: These findings indicate that activation of the Akt pathway represents a likely mechanism mediating the hypertrophic effect of increased NHE1 activity in the GK model of type 2 diabetes. © 2007 Springer-Verlag.