RUBIDIUM AND CESIUM FLUXES IN MUSCLE AS l~ELATED TO T H E MEMBRANE POTENTIAL* BY RAYMOND A. SJODIN

The reduction of membrane potential in frog sartor/us muscle produced by rubidium and cesium ions has been studied over a wide concentration range and compared with depolarization occasioned by potassium ions. The constant field theory of passive flux has been used to predict the potential changes observed. The potential data suggest certain permeability coe~eient ratios and these are compared with ratios obtained from flux data using radioactive tracers. The agreement of the flux with the potential data is good ff account is taken of the inhibition of potassium flux which occurs in the presence of rubidium and cesium ions. A high temperature dependence has been observed for cesium influx (Ql0 = 2.5) which is correlated with the observation that cesium ions depolarize very little at low temperatures. The observations suggest that cesium ions behave more like sodium ions at low temperatures and more like potassium ions at room temperature with respect to their effect on the muscle ~ resting potential. The constant field theory of p~sive ion flux appears to be in general agreement with the experimental results observed if account is taken of the dependence of permeability coe~dents on the concentrations of ions used and of possible interactions between the permeabilities of ions.