Outflux of various phosphates during membrane depolarization of excitable tissues

Abstract

The main purpose of the present work was to study in detail the outflux of P³² from excitable tissues accompanying membrane depolarization or electrical excitation. With the use of P³² as a tracer, it has been demonstrated that orthophosphate and a number of organic phosphates slowly diffuse out of nerve and muscle even after 2 hr of exposure to Ringer's solution. On exposure to calcium-free or potassium-rich media, or during electrical excitation, there is a considerable increase in the outflux of a number of acid-soluble phosphates, particularly orthophosphate and adenosinetriphosphate. Further evidence in support of this concept was based on the fact that the radioactive specific activity of the diffusible phosphates was greater than the internal phosphates of excitable tissues. Since all these procedures are known to result in depolarization of excitable tissues, there was reason to believe that the outflux of muscle phosphates was somehow related to the physicochemical changes associated with membrane depolarization. The changes in the outflux of P³² from the muscle or nerve, either stimulated or soaked in calcium-free or potassium-rich media, appear to be related to the changes in the membrane potential.