Differential gene transcriptional regulation of Gi isoforms and Gs protein expression in diabetic rat hearts

Many cardiac diseases can be associated with alterations in the function and quantity of G proteins. We examined the gene expressions and protein levels of Gi-1 α, Gi-2 α, Gi-3 α and Gs α in ventricular myocardial preparations from rats 4–6 weeks after induction of diabetes with streptozotocin in comparison with those from age-matched control rats. Diabetic rat myocardium exhibited reductions in the protein levels of Gi-2 α and Gi-3 α by 22±2% and 57±2%, respectively. In diabetes, 22% and 53% reductions in myocardial mRNA levels of Gi-2 α and Gi-3 α were observed. Although a faint protein signal of Gi-1 α was detectable, no apparent expression of mRNA for Gi-1 α was found in either control or diabetic myocardium. The reduced protein and mRNA levels of Gi-2 α and Gi-3 α were prevented by insulin therapy. No change was found in the protein and mRNA levels of Gs α in diabetic myocardium. In conclusion, diabetes leads to a differential regulation of protein expressions of Gi α isoforms and Gs α in ventricular myocardium. The reduced expression of Gi-2 α and Gi-3 α proteins can be explained, at least in part, by the decreases in the transcriptional levels.