ATPase activity, IF1 content, and proton conductivity of ESMP from control and ischemic slow and fast heart-rate hearts

Abstract

Earlier studies by Rouslin and coworkers showed that, during myocardial ischemia in slow heart-rate species which include rabbits and all larger mammals examined including humans, there is an IF1-mediated inhibition of the mitochondrial ATPase due to an increase in the amount of IF1 bound to the ATPase (Rouslin, W., and Pullman, M.E., J. Mol. Cell. Cardiol. 19,661-668, 1987). Earlier work by Guerrieri and colleagues demonstrated that IF1 binding to bovine heart ESMP was accompanied by parallel decreases in ATPase activity and in passive proton conduction (Guerrieri, F., et al., FEBS Lett. 213, 67-72, 1987). In the present study rabbit was used as the slow heart-rate species and rat as the fast heart-rate species. Rat is a fast heart-rate species that contains too little IF1 to down regulate the ATPase activity present. Mitochondria were prepared from control and ischemic hearts and ESMP were made from aliquots by sonication at pH 8.0 with 2 mM EDTA. Oligomycin-sensitive ATPase activity and IF1 content were measured in SMP prepared from the control and ischemic mitochondrial samples. After identical incubation procedures, oligomycin-sensitive ATPase activity, oligomycin-sensitive proton conductivity, and IF1 content were also measured in ESMP samples. The study was undertaken to corroborate further what appear to be fundamental differences in ATPase regulation between slow and fast heart-rate mammalian hearts evident during total myocardial ischemia. Thus, passive proton conductivity was used as an independent measure of these regulatory differences. The results show that, consistent with the low IF1 content of rat heart cardiac muscle mitochondria, control rat heart ESMP exhibit approximately twice as much passive proton conductivity as control rabbit heart ESMP regardless of the pH of the incubation and assay. Moreover, while total ischemia caused an increase in IF1 binding and a commensurate decrease in passive proton conductivity in rabbit heart ESMP regardless of pH, neither IF1 content nor proton conductivity changed significantly in rat heart ESMP as a result of ischemia.

Excessive ATP hydrolysis in ischemic myocardium by mitochondrial F1F0-ATPase: effect of selective pharmacological inhibition of mitochondrial ATPase hydrolase activity

“…Determination of mitochondrial concentrations of IF 1 show some species differences. Rouslin et al (24,26) grouped different species into several categories according to heart rate, IF 1 content, or IF 1 affinity. Larger animals (slow heart rate species) such as dogs express relatively higher amounts of IF 1 , although the study by Jennings et al (11) showed that during ischemia, inhibition of the ATP hydrolase activity was incomplete.…”

“…The inhibition of the ATP hydrolase activity by IF 1 is reversible upon restoration of the mitochondrial electrochemical gradient and increased pH as might be seen during reperfusion (30). IF 1 may not play an important role in inhibiting ATPase activity in "fast" heart rate species such as the rat, where it is not as highly expressed compared with the dog and rabbit (23,24,26). Nevertheless, the unique feature of IF 1 is that it specifically inhibits ATP hydrolase activity rather than ATP synthetic activity, showing that it is possible to selectively inhibit hydrolase activity.…”

“…In "slow" heart rate species such as dogs, humans, and rabbits, the amount of ATP hydrolyzed by mitochondrial ATPase during ischemia is thought to be significantly reduced by the reversible binding of the IF 1 protein (26). This small 80-amino acid protein specifically inhibits the ATP hydrolase activity of F 1 F 0 -ATPase (5,20,26).…”

“…This small 80-amino acid protein specifically inhibits the ATP hydrolase activity of F 1 F 0 -ATPase (5,20,26). The binding of IF 1 to F 1 F 0 -ATPase is optimal at pH 6.7 and requires the hydrolysis of ATP in the absence of an electrochemical gradient, conditions also seen during myocardial ischemia (13,19).…”

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

“…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.…”