Dynamic regulation of the mitochondrial proton gradient during cytosolic calcium elevations.

ABSTRACT: Mitochondria extrude protons across their inner membrane to generate the mitochondrial membrane potential (??(m)) and pH gradient (?pH(m)) that both power ATP synthesis. Mitochondrial uptake and efflux of many ions and metabolites are driven exclusively by ?pH(m), whose in situ regulation is poorly characterized. Here, we report the first dynamic measurements of ?pH(m) in living cells, using a mitochondrially targeted, pH-sensitive YFP (SypHer) combined with a cytosolic pH indicator (5-(and 6)-carboxy-SNARF-1). The resting matrix pH (?7.6) and ?pH(m) (?0.45) of HeLa cells at 37 °C were lower than previously reported. Unexpectedly, mitochondrial pH and ?pH(m) decreased during cytosolic Ca(2+) elevations. The drop in matrix pH was due to cytosolic acid generated by plasma membrane Ca(2+)-ATPases and transmitted to mitochondria by P(i)/H(+) symport and K(+)/H(+) exchange, whereas the decrease in ?pH(m) reflected the low H(+)-buffering power of mitochondria (?5 mm, pH 7.8) compared with the cytosol (?20 mm, pH 7.4). Upon agonist washout and restoration of cytosolic Ca(2+) and pH, mitochondria alkalinized and ?pH(m) increased. In permeabilized cells, a decrease in bath pH from 7.4 to 7.2 rapidly decreased mitochondrial pH, whereas the addition of 10 ?m Ca(2+) caused a delayed and smaller alkalinization. These findings indicate that the mitochondrial matrix pH and ?pH(m) are regulated by opposing Ca(2+)-dependent processes of stimulated mitochondrial respiration and cytosolic acidification.

SUBMITTER: Poburko D 

PROVIDER: S-EPMC3064219 | biostudies-literature | 2011 Apr

REPOSITORIES: biostudies-literature