Contribution of ATP synthase to stimulation of respiration by Ca/sup 2+/ in heart mitochondria

Abstract

A variety of experimental conditions were applied with the aim to estimate the correlation between the contribution of ATP synthase to the respiratory flux control and the calcium-induced activation of succinate oxidation in heart mitochondria isolated from rat, rabbit and quinea pig. The sensitivity of respiration in heart mitochondria to the decrease in temperature from 37°C to 28°C decreases in the order rabbit> guinea pig > rat. Ca²+ effect on succinate oxidation rate in state 3 respiration was species- and temperature-dependent and ranged from 0 (rat, 37°C) to +44% (rabbit, 28°C). For mitochondria from all experimental animals, the increase of Ca²+ in physiological range of concentration did not change state 2 respiration rate, and the stimulatory effect of Ca²+ on state 3 respiration was more pronounced at 28°C than at 37°C. The respiratory subsystem was sensitive to Ca²+ ions only in rabbit heart mitochondria. A high positive correlation between Ca²+ ability to stimulate succinate oxidation in state 3 and the control exerted by ATP synthase over the respiratory flux provides argument confirming stimulation of ATP synthase by Ca²+ ions.