Abstract
The effects of low temperature on uptake and release of (45)Ca(2+) were studied with sound, well-coupled mitochondria extracted at room temperature from avocado (Persea americana Mill, cv Fuerte) fruits. Low Ca(2+) concentrations (10 micromolar) were employed to simulate physiological conditions. At 25 degrees C, the rate of Ca(2+) uptake decreased with time, whereas at 5 degrees C the initial rate, though lower, remained linear. As a consequence total uptake at 5 degrees C was substantially greater than at 25 degrees C for periods greater than 5 min. Preincubation of mitochondria at 5 degrees C enhanced subsequent Ca(2+) uptake at 25 degrees C. Ca(2+) uptake was inhibited by carbonyl cyanide-m-chlorophenyl hydrazone (CCCP) and by ruthenium red, but neither KCN nor salicylhydroxamic acid separately or together had any major inhibitory effect. Preloaded mitochondria held for 60 min in a Ca-free medium lost little Ca(2+) at 25 degrees C and none at 5 degrees C, except in the presence of ruthenium red or CCCP.