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Objectives and Results

The aims of the experiments conducted so far have been to verify the following hypothesis; As pacing frequency is increased, cytosolic calcium and work increases. This causes a calcium independent fall of NADH (because mitochondrial calcium is still low), and indicates stimulation of oxidative phosphorylation by another control signal (possibly ADP). After a few seconds, mitochondria takes up calcium causing NADH (and possibly ADP) to recover to control values. This rise of NADH presumably restores the mitochondrial energetic state, permitting it and other cellular processes to function normally during demands of increasing energy consumption. Indeed, the results demonstrated that increased pacing frequency and work caused a fall of NADH that only depended on work level but not on calcium, and that the reverse was true for the NADH recovery which only depended on calcium but not on work level. The accompanying illustration shows that, in cardiac muscle, increasing pacing frequency and therefore cytosolic calcium results in increased NADH recovery. This complicated 3D-graph was created in a matter of minutes, demonstrating how virtually any component of a plot can be manipulated through interactions with the mouse and dialog boxes. The use of such a 3D-graph is important in order to illustrate the independent effects of the two controlling variables; Work (proportional to Average Force development) and calcium (proportional to pacing frequency). By varying pacing frequency, both calcium and work is varied, and by varying muscle stretch (sarcomere length) only work is affected. The spheres are the data points for NADH recovery, resulting from a particular combination of sarcomere length and frequency. The wire-frame surface was calculated by using a customer written function, fitting the NADH recovery data simultaneously to both frequency and Average Force (i.e. fitting Z to both X and Y). Also shown are the projections of the spheres on the Average Force-frequency plane illustrating the relationship between these two variables.

Ongoing Research

Loyola researchers are currently engaged in further investigations of the importance of calcium as a controlling factor of oxidative phosphorylation during normal and pathophysiological conditions. They are attempting to directly determine the dynamic relationships of cytosolic calcium versus work, mitochondrial versus cytosolic calcium, and mitochondrial NADH versus mitochondrial calcium. From these studies, they expect to determine the detailed mechanisms of how calcium is involved in the regulation of cardiac energetics, and if alterations of these mechanisms may be correlated with cardiac diseases .

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