Contribution of ATP synthase to stimulation of respiration by Ca2+ in heart mitochondria.

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 guinea pig. The sensitivity of respiration in heart mitochondria to the decrease in temperature from 37 degrees C to 28 degrees 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 degrees C) to +44% (rabbit, 28 degrees 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 degrees C than at 37 degrees 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.