Ca2+ transport in mitochondria of the ciliate protozoan Tetrahymena pyriformis

Mitochondria isolated from the late-exponential non-shaken culture of the ciliate protozoan Tetrahymena pyriformis GL was investigated. The presence of energy-dependent Ca2+ transport system was shown. In the main the properties of this system have been essentially the same as in mitochondria of vertebrate organisms. The isolated mitochondria contained 23 +/- 5 ng-ion Ca2+ per mg of protein. The intramitochondrial free concentration of Ca2+ was measured in the presence of uncoupler FCCP with the use of fluorescent Ca2+ chelator chlortetracycline and null point titration method. In the absence of phosphate, free [Ca2+] varied from 1 to 2.5 mM depending on the internal Ca2+ content. In the presence of 2 mM phosphate, free [Ca2+]in has not exceeded 0.1-0.3 mM. It was shown that ruthenium red and Mg2+ in different manner have an inhibitory effect on Ca2+ transport. Besides this, Mg2+ also has a stabilizing effect on mitochondria, possibly, by preventing passive ions leaks across the membrane.