Cardiac function is controlled by neurotransmitters, neuromodulators, and drugs which bind to specific receptors located on the cardiac membrane. These receptors interact with various effector systems to regulate cellular activity. It is now recognized that adenosine is locally released in the heart and that it acts on specific extracellular, membrane bound receptors to cause decreases in the rate and force of contraction of the heart. Furthermore, it is known that the rate of adenosine release in the myocardium is increased during exercise, hypoxia/ischemia and in the failing heart. While we know that cardiac adenose receptors (AdoRs) couple to K channels in the atria and to adenylate cyclase in both the ventricle and the atria, we know little about the cardiac AdoR itself. This is largely due to the relative paucity of AdoRs in cardiac tissue. The long term goal of this project is to isolate and characterize cardiac AdoRs. Cardiac AdoRs have characteristics similar to the A(1) AdoR which is present in the brain. As the concentration of these receptors is much higher in the brain compared to the heart, our initial goal is to purify the brain A(1) AdoR. We will do this using a combination of affinity chromatography and classical protein purification techniques; polyclonal antibodies against this AdoR and peptide fragments thereof will subsequently be prepared. A combination of affinity chromatography, protein purification techniques and immunoaffinity chromatography will be used to isolate cardiac AdoRs. Affinity labeling and peptide mapping experiments will be performed to compare the properties of the cardiac and neural AdoR to determine if subtypes of AdoRs exist. Furthermore, we will compare the properties of A(1) AdoRs in atria and ventricle in order to begin to probe the possibility that different types of A(1) receptors couple to different effectors, e.g., K Channels and adenylate cyclase.
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