ATP depletion and mitochondrial functional loss during ischemia in slow and fast heart-rate hearts

Abstract

In the present study, isolated dog and rat hearts were perfused in the Langendorff mode with Krebs bicarbonate buffer in the absence and presence of 10(-5) M oligomycin. The perfusion protocols employed allowed tissue pH to drop during subsequent ischemic incubations essentially as it would in blood-perfused hearts. Tissue pH, ATP, lactate, and mitochondrial respiratory function were measured during the course of subsequent zero-flow ischemic incubations. The adenosinetriphosphatase (ATPase) activities attributable to both mitochondrial and nonmitochondrial ATPases in sonicated heart homogenates and the actomyosin ATPase in isolated cardiac myofibrils were measured in both species. Consistent with earlier results with a different model in which tissue pH was buffered during the ischemic incubations [W. Rouslin, J. L. Erickson, and R. J. Solaro. Am. J. Physiol. 250 (Heart Circ. Physiol. 19): H503-H508, 1986], the inhibition of the mitochondrial ATPase in situ by oligomycin markedly slowed both tissue ATP depletion and the loss of mitochondrial function during ischemia in the dog. However, oligomycin had only a very small and transient effect on ATP depletion and mitochondrial function in the rat. This was apparently so because of the fivefold higher rate of glycolytic ATP production as well as the nearly threefold higher total nonmitochondrial ATPase activity of ischemic rat compared with ischemic dog heart. These results suggest that although the inhibition of the mitochondrial ATPase makes a major contribution to ATP conservation in ischemic dog heart, it makes only a very small contribution in rat.

Pharmacological Profile of the Selective Mitochondrial F1F0 ATP Hydrolase Inhibitor BMS‐199264 in Myocardial Ischemia

“…Aurovertin B binds between the subunits catalytic F 1 domain of the F 1 F 0 ATPase, where it prevents the conformational changes required for the catalytic cycle of this enzyme, while oligomycin binds to the F 0 domain [42] and blocks proton flow. Jennings et al [9], Vuorinen et al [12], and studies from Rouslin's group [10] showed that the nonselective F 1 F 0 ATPase inhibitor oligomycin B reduced the rate of ATP depletion in rats and dogs. ATP was measured during ischemia per se, and no effects on reperfusion or preischemic ATP were measured.…”

“…Its activity is maximal at a pH of 6.8 and occurs in the absence of a proton motive force, conditions associated with ischemia. While it seems intuitive that this hydrolase inhibition can prevent wasteful ATP hydrolysis during ischemia, this inhibition of the F 1 F 0 ATP hydrolase is not complete as F 1 F 0 ATPase inhibitors such as oligomycin and aurovertin B reduce the rate of ATP decline, suggesting incomplete inhibition of the hydrolase activity [9][10][11][12]. This will be discussed in more detail later.…”

“…IF-1 in the heart is expressed differently in several mammalian species, and this has been subdivided into "fast heart rate species" (rat, mice, and birds) that express low levels of IF-1 and "slow heart rate species" (dogs and rabbits) that express high levels of IF-1 [10,[47][48][49]. It is presently unclear how these differences can affect the pathogenesis of ischemia in the different species.…”

“…Perhaps another pool of ATP exists that can be manipulated pharmacologically, which might be more relevant for the pathogenesis of ischemia. Work published by several groups [8][9][10][11][12] showed that the mitochondrial F 1 F 0 ATP synthase paradoxically becomes an ATP hydrolase under ischemic conditions and that the nonselective (inhibits both synthase and hydrolase functions) F 1 F 0 ATP synthase/hydrolase inhibitors oligomycin B and aurovertin B significantly attenuate the rate of ATP hydrolysis in ischemic myocardium. While there are differences in the reports as to the precise percentage of ATP lost to this mechanism, all studies show a significant percentage to be due to the F 1 F 0 ATP hydrolase.…”

Difference in the Cardioprotective Mechanisms Between Ischemic Preconditioning and Pharmacological Preconditioning by Diazoxide in Rat Hearts

“…Dzeja et al recently found that DZ attenuates cellular and mitochondrial ATPase activities. 34 It appears that reduced ATP degradation during ischemia because of the inhibitory effect of DZ on cellular and mitochondrial ATPase activities preserves the mitochondrial respiratory chain 35 and sarcolemmal integrity, 36 and thereby is associated with cardioprotection in rat hearts.…”