This proposal will investigate the effects of selective and combined inhibition of glycolytic and oxidative metabolism on cardiac function, specifically membrane K+ conductance, action potential configuration, and the development of contracture. In the first project, the patch clamp technique will be applied to isolated ventricular myocytes to record whole cell and single K+ channel currents in order to: i) characterize the effects of selective vs. combined metabolic inhibition on K+ currrents, ii) determine whether various sequelae of metabolic inhibition e.g. lactate accumulation, acidosis, lysophosphoglyceride accumulation, free radical generation, etc. cause or aggravate the abnormalities in membrane K+ conductance during metabolic inhibition, iii) characterize more fully the pharmacologic responses and ATP dependence of the previously described ATP sensitive K+ channel, e.g. how is the channel affected by various blockers of ionic currents, and is the channel more sensitive to [ATP] or the ATP phosphorylation potential? iv) determine whether glycolytically generated ATP is a preferential source of ATP for this channel. The next two projects will focus on the role of glycolysis in preserving cardiac function during hypoxia and low flow ischemia. In the first, the effects of elevated (50 mM) glucose on action potential shortening during hypoxia (in the presence and absence of beta blockade) will be contrasted in the arterially perfused rabbit interventricular septum vs. the superfused rabbit papillary muscle. In the second, contracture induced by hypoxia and by selective inhibition of glycolysis with iodoacetate will be compared in the septal preparation. The effects of interventions affecting cellular Ca++ homeostasis on contracture development under these conditions will be studied. Using Ca++ microelectrodes changes in [Ca++]i will be correlated with the development of contracture. A method for monitoring the contribution of exogenous glucose utilization vs. glycogenolysis to total glycolytic flux will be applied during hypoxia and iodoacetate intoxication to determine whether any consistent relationship between contracture development and one of these components of glycolytic flux exists. These studies will hopefully contribute significantly to understanding the relationship between specific metabolic pathways and cardiac function, and further enhance our knowledge of the pathophysiology of impaired metabolism as it relates to myocardial ischemia.
Showing the most recent 10 out of 27 publications
