Proton electrochemical potential in steady state rat liver mitochondria

Delta approximately muH has been determined in steady state mitochondria by measuring the magnitude of delta pH on the distribution of acetate and of deltapsi on the distribution of K+, tetraphenylphosphonium, Ca2+, Sr2+ and Mn2+. (1) The matrix concentration of divalent cations has been calculated from the total cation uptake, from the increase of matrix volume and from the ESR sextet signal of Mn(H2O)L2+. The [cat2+]i based on osmotic data is about five times higher than that based on ESR measurements. The [cat2+]i based on total uptake is much higher than that based on osmotic data at low cation/protein ratios. (2) In the presence of 10 mM acetate the maximal deltapsi on Ca2+ is about 130 mV and on Sr2+ is 95 mV. Deltapsi on Mn2+ is 91 or 109 mV, according to whether [cat2+-a)i is calculated from ESR or osmotic data. Under the same conditions, deltapH is about 60 mV. Hence delta approximately muH on divalent cations is between 151 and 190 mV. (3) Deltapsi on K+, in valinomycin treated mitochondria with 10 mM acetate or 2 mM Pi, drops from 200 mV, at low [K+]0 to almost zero parallel to the increase of [K+]0. DeltapH is 30 mV at low [K+]0 and about 42 mV at 600 muM K+. Hence delta approximately muH drops from 22m mV lower values with the increase of [K+]0. (4) Maximal deltapsi on triphenylmethylphosphonium is 140 mV. (5) When delta approximately muH is measured simultaneously on divalent cations and on K+, the values on K+ tend to approach those on Ca2+ while those on Sr2+ are about 50 mV lower. (6) It is concluded that the steady state mitochondrial energy potential is equivalent to a delta approximately muH between 150 and approx. 190 mV.