Cation Uptake as the Basis for Production of Proton Pulses by Mitochondria at the Anaerobic‐Aerobic Transition

1 Calcium movement and proton pulse production by mitochondria have been studied using pH- and K+-sensitive glass electrodes and the Ca++ indicator murexide. 2 Anaerobic treatment led to the release of free Ca++ into the medium, the quantity depending on the preparative procedure and the composition of the medium. 3 The ejection of protons by anaerobic mitochondria given small additions of oxygen was accompanied by the uptake of approximately equal numbers of calcium ions. Addition of ethylene glycol bis (β-aminoethyl)-N, N′-tetraacetic acid (EGTA) reduced the proton pulses to about 40% of their maximum size in KCl medium, and to 5% in a sucrose medium. 4 Mitochondria treated with EGTA and valinomycin gave proton pulses that were accompanied by approximately equal uptakes of K+. 5 Mitochondria kept anaerobic for 20 min and then aerated were found to be without respiratory control by ADP unless EGTA was added before aeration. 6 It is concluded that the production of proton pulses by untreated mitochondria at the anaerobic-aerobic transition occurs only under conditions where sufficient free Ca++ has leaked out to allow energy-dependent exchange between external Ca++ and internal protons.