Subcellular distribution of phosphagens in isolated perfused rat heart

Abstract

~~p~rt~e~t of ~~d~~~l B~o~h~?~~istr~l, ~~~~~~~s~ty of Zulu, K~j~~~~i~tie 52 A, SF-95225 Oufu 22, Finland It has been suggested that the oxygen consunlption of the mitochondrial respiratory chain is regulated by the extranlitochondrial ATP/ADP X P, ratio and that a near-equilibrium exists between the oxidation-reduction reactions of the mitochondrial respiratory chain and the phosphorylation of cytosolic ADP [ 11. Data on the situation in intact tissues have been largely obtained by measurements of total average concentra. tions of the reactants [2], but corroboration of the near-equilibrium hypothesis [3] of respiratory control needs data on the concentrations of the reactants in specified intracellular compartments. The isolated perfused rat heart has been employed in studies on the regulation of cellular respiration, and total average concentrations of ATP, ADP, Pi, creatine and creatine phosphate used in calculations of the extramitochondrial phosphorylation potential [4,5]. Here, advantage has been taken of the method of tissue fractionation in non-aqueous media [6] to measure the cytosolic and m~tochondrial phospl~orylation potentials. The results show that the error in estimating the cytosolic phosphorylation potential from total tissue concentration of the reactants is quite small when calculated from the creatine kinase equilibrium. The results are compatible with a near-equilibrium between the mitochondrial respiratory chain and the cytosolic adenylate system. Changes in the distribution of the adenylates across the mitochondrial membrane upon transitions in the cellular ATP consumption indicate that the ~nitochondrial membrane potential and transmembrane pH difference also change.