Diabetic Autonomic Neuropathy (DAN) is a debilitating complication of diabetes involving multiple organ systems including the gastrointestinal, genitourinary, cardiovascular, and neurovascular systems, which result in increased patient morbidity and mortality. The cardiac complications of autonomic neuropathy in diabetic patients are associated with the most severe prognostic consequences including predisposition to arrhythmia and sudden death. Therefore, early detection of cardiac autonomic dysfunction is of great importance in prevention of the more advanced stages of the disease. The autonomic nervous system modulates the electrical and contractile activity of the heart via the interplay of sympathetic and parasympathetic activity. The homeostatic regulation of the heart is mainly controlled by the extracellular signals transduced by the heterotrimeric G protein-coupled receptors (GPCRs): sympathetic responsiveness involves the ?-adrenergic receptor family and the stimulatory G protein Gs while parasympathetic responsiveness involves the M2 muscarinic receptor and the inhibitory G protein Gi2. Our recent studies suggested a close correlation between the parasympathetic response of the heart and the level of Gai2, the a subunit of Gi2, in the lymphocytes of hypercholesterolemia patients treated with pravastatin. The goal of this application is to test the intriguing hypothesis that Gai2 levels in the lymphocytes might constitute a molecular marker for the autonomic dysfunction of the heart in diabetics. Preliminary data demonstrated that the type I diabetic Akita mouse has a parasympathetic dysfunction of the heart associated with a markedly higher incidence of ventricular tachycardia following myocardial infarction compared with non-diabetic control mice. Based on our recent studies with these preliminary data, the experiments proposed in this R21 application will use this type I diabetic Akita mouse to test two major hypotheses: 1) that the parasympathetic dysfunction of the heart in the type I diabetic Akita mouse is associated with a decrease in Gai2 levels in the lymphocytes from this diabetic mouse and; 2) that an imbalance in the Gai2 / Gas ratio in the lymphocytes of the type I diabetic Akita mouse is associated with an increased incidence of spontaneous arrhythmias after myocardial infarction in this diabetic mouse. This study might offer a simple molecular marker for alterations of cardiac autonomic modulation at the earliest possible stages of DAN and for the predisposition to the development of arrhythmia, which may be of prognostic importance in the diagnosis and treatment of DAN. ? ? ?
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