Molecular biological, biochemical and electrophysiological approaches will be used in combination in order to determine the molecular basis for the ATP-sensitive potassium channel (IKATP) in the heart. IKATP is responsible for a number of different functions in the heart including coupling the membrane potential to the metabolic state of the cell, and cardioprotection following ischemia. IKATP is also expressed in pancreatic Beta-cells where it serves to mediate insulin release in response to glucose levels. In the brain IKATP serves an anti-seizure activity in the substantia nigra and controls feeding behavior in the ventral hypothalamus. The molecular basis for IKATP has been identified in pancreatic beta cells, and found to be comprised of two different subunits, one is the sulfonylurea receptor (SUR), the other is a novel inward rectifier (Kir6.2). Using these two clones as probes the cardiac member of the IKATP family will be cloned. The identity of these clones will be verified through heterologous expression of the cDNAs followed by detailed electrophysiological analysis. The structures of the individual subunits will provide valuable information about how the channel properties are specified, since IKATP in heart and pancreas differ in their conductance and pharmacological properties. Knowing the structure of the cardiac IKATP could also be useful in designing drugs which target the pancreatic form of IKATP specifically. These drugs could be used to treat diabetes without fear of pleiotropic effects. Also of interest is how the cardiac IKATP is expressed exclusively in the heart, and more specifically at higher levels in the ventricles than in the atria. In order to understand how this is achieved, the regulatory regions of the genes will be cloned and analyzed in transient transfection analyses in both cardiac and non-cardiac cells.
