B.: Metabolic aspects of the relationship between contractility and membrane potentials of the rat atrium. Circulation Research 4: 618

Some of the relationships between metabolism, membrane potentials and contractility in cardiac tissue have emerged from a study of the effects of anoxia, depletion of substrate and dinitrophenol on the rat atrium. The repolarization phase of the action potential was shown to be particularly sensitive to disturbances in metabolism. Depression of metabolism resulted in a more rapid re-polarization, which may provisionally be interpreted as an acceleration of K+ efflux; restoration of metabolism reversed this effect. A concept relating membrane potentials and metabolism is pre-sented, involving the presence of bound ATP within the membrane. CERTAIN effects of anoxia on the elec-tric characteristics of the mammalianventricle in situ were noted by the use of contact electrodes ' and a detailed study with intracellular microelectrodes has been re-ported on papillary muscle and Purkinje tis-sue.1 However, no quantitative investigation has been made of the changes in membrane potentials and contractility of atrial tissue under anoxic conditions or during disturbance of the metabolism by other means. The metab-olism of a tissue may be most readily altered by removal of oxygen, removal of oxidizable substrate or by interference with any enzy-matic step in the transfer of energy from sub-strate to the contractile process; all of these methods have been utilized in the present study. METHODS The membrane potentials and mechanical activity of rat atria electrically stimulated at a rate of 200/ min. in Krebs-Ringer-biearbonate medium at pH 7.4 and 30 C. were determined simultaneously using microelectrodes and a sensitive strain gage as pre-viously described. ' A state of anoxia was produced by replacing the usual 95 per cent 0;, 5 per cent COj mixture with 95 per cent Nj, 5 per cent CO5. Solutions to be added were prepared in the tissu