OXIDATIVE-PHOSPHORYLATION AND THE REALKALINIZATION OF INTRACELLULAR PH DURING RECOVERY FROM ANOXIA IN ARTEMIA-FRANCISCANA EMBRYOS

The contribution of mitochondrial oxidative phosphorylation to the rea lkalinization of intracellular pH (pH(i)) and resynthesis of purine nu cleotides during recovery from anoxia was investigated in embryos of A rtemia franciscana by assessing the sensitivity of mitochondrial respi ration to pH, calculating proton consumption by oxidative phosphorylat ion, and measuring changes in pH(i) using P-31 nuclear magnetic resona nce. Following short-term anoxia, pH(i) increased from 6.7 to 7.7 duri ng 20 min of aerobic recovery and was temporally correlated with a lar ge increase in ATP. State 3 respiration rates of isolated mitochondria were not substantially compromised at the acidic pH corresponding to the pH(i) during anoxia (pH 6.3-6.8) compared to values obtained at pH 7.7. Both state 3 respiration rates and respiratory control ratios ex hibited broad, substrate-specific pH optima, whereas state 4 respirati on rates increased gradually with increasing pH. P:O flux ratios were near their mechanistic limits and did not vary appreciably with pH bel ow 7.5. Estimates of intracellular buffering capacity indicate that be tween 18 and 37 mmol H+ (1 cytosol)(-1) must be consumed to elevate pH (i) from 6.7 to 7.7. Phosphorylation of mono- and diphosphate purine-n ucleotides during the first 20 min of recovery may account for the con sumption of up to 4.79 mmol H+ (1 cytosol)(-1). An additional 4.77 to 8.18 mmol H+ (1 cytosol)(-1) may be consumed through the oxidation of mono- or dicarboxylic acids, respectively, in the Krebs cycle. Taken t ogether, these data are consistent with a role for oxidative phosphory lation in the realkalinization of pH(i) and resynthesis of purine nucl eotides in A. franciscana embryos during recovery from anoxia.