Temperature effects on pH of mitochondria isolated from carp red muscle

Mitochondria isolated from red muscle of carp (Cyprinus carpio) were used to investigate the effects of temperature and extramitochondrial pH (pHe) on the mitochondrial pH gradient and respiratory properties. Mitochondria from animals acclimated to 10 degrees C were isolated and incubated in KCl-based media with 0.2 mM lauroylcarnitine (C-12) as substrate. Maximal respiratory control ratios (RCR = state 3/state 4) were 16-18 between pH 6.7 and 7.4 at 10 degrees C; RCR values were 9-12 between pH 6.5 and 7.1 at 30 degrees C. Changes in RCR values were due primarily to changes in the state 3 rate (in the presence of ADP). Mitochondrial pH was determined by measuring 5,5-[2-14C]dimethyloxazolidine-2,4-dione distribution, using [14C]sucrose as an extramatrical marker. The pH gradient was inversely related to pHe. At any particular pHe, the mitochondrial pH gradient decreased with increasing temperature. However, if pHe was varied in the same manner that intracellular pH changes with temperature in vivo, the pH gradient was maintained constant at approximately 0.4 U at 10, 20, and 30 degrees C. These data suggest that carp red muscle mitochondria defend an appropriate mitochondrial pH gradient with temperature-induced changes in intracellular pH.