The long-term objective of this proposal is to determine how metabolic abnormalities common to ischemia and congestive heart failure produce defects in cellular excitation-contraction (E-C) coupling. These defects are responsible for the contractile abnormalities that typify cardiogenic shock in patients sustaining a large myocardial infarction or suffering from end-stage dilated and ischemic cardiomyopathies. We have three specific aims: 1) We will investigate the metabolic regulation of cardiac E-C coupling gain and subcellular Ca2+ release events in adult ventricular myocytes. A major goal is to determine whether E-C coupling is preferentially dependent upon ATP derived from glycolysis versus oxidative metabolism; 2) We will determine how single Ca2+ channel properties are regulated by glycolytic versus oxidative metabolism. We will also determine the relative roles of the Ca2+ current, and the ryanodine receptor, on changes in Ca2+ spark probability during metabolic inhibition; 3) We will study alterations in total transmembranous Ca2+ flux produced by metabolic inhibition, and determine the extent to which Ca2+ current activates sodium-calcium exchange under these conditions. Our general approach is to study the response of subcellular Ca2+ movements and transmembranous Ca2+ fluxes to metabolic inhibitors, in patch clamped isolated ventricular cardiac myocytes from rats and rabbits loaded with fluorescent Ca2+ indicators. Metabolic inhibitors will be chosen to block, alternatively, glycolytic metabolism, oxidative metabolism, or both glycolytic and oxidative metabolism simultaneously. We will use novel confocal imaging strategies to record subcellular Ca2+ movements during metabolic stress with unusually high spatial and temporal resolution. We will, for the first time, assess the effects of metabolic inhibition on the single channel properties of L-type Ca2+ channels in cell-attached patches on rat and rabbit ventricular myocytes. We will use a novel epifluorescence approach to sort out the effects of metabolic inhibition on the complex interaction between L-type Ca2+ channels and the sodium-calcium exchanger. A better understanding of these issues will assist in the development of new therapies to restore contractile function in patients with cardiac failure.
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