ATP Synthase K+- and H+-Fluxes Drive ATP Synthesis and Enable Mitochondrial K+-Uniporter Function: I. Characterization of Ion Fluxes

ATP synthase (F1Fo) synthesizes daily our body's weight in ATP, whose production-rate can be transiently increased several-fold to meet changes in energy utilization. Using purified mammalian F1Fo-reconstituted proteoliposomes and isolated mitochondria, we show F1Fo can utilize both Delta psi(m)-driven H+- and K+-transport to synthesize ATP under physiological pH = 7.2 and K+ = 140 mEq/L conditions. Purely K+-driven ATP synthesis from single F1Fo molecules measured by bioluminescence photon detection could be directly demonstrated along with simultaneous measurements of unitary K+ currents by voltage clamp, both blocked by specific F-o inhibitors. In the presence of K+, compared to osmotically-matched conditions in which this cation is absent, isolated mitochondria display 3.5-fold higher rates of ATP synthesis, at the expense of 2.6-fold higher rates of oxygen consumption, these fluxes being driven by a 2.7:1 K+: H+ stoichiometry. The excellent agreement between the functional data obtained from purified F1Fo single molecule experiments and ATP synthase studied in the intact mitochondrion under unaltered OxPhos coupling by K+ presence, is entirely consistent with K+ transport through the ATP synthase driving the observed increase in ATP synthesis. Thus, both K+ (harnessing Delta psi(m)) and H+ (harnessing its chemical potential energy, Delta mu(H)) drive ATP generation during normal physiology.

Automated summary

ATP synthase can utilize both Delta psi(m)-driven H+- and K+-transport to synthesize ATP under physiological conditions. The presence of K+ increases ATP synthesis rate in isolated mitochondria while also increasing oxygen consumption rate. The data obtained from purified F1Fo single molecule experiments are consistent with the functional data observed in intact mitochondria.