Physical and metabolic factors in diffusion of solutes into tissue slices

Abstract

Although the physical factors influencing the diffusion of solutes (such as oxygen) into tissue slices have been clearly defined, conflicting results obtained with this approach indicate that certain of the necessary considerations are not being satisfied. The application of histochemical procedures, such as the tetrazolium technique, to the study of fresh tissue slices provides a means of exploring directly some of the complexities involved since the actual depth of penetration of the solute can be determined by histological inspection. The penetration of tetrazolium salts was found to be influenced in a predictable manner by concentration and by tissue activity as could be anticipated from Warburg's formula governing the diffusion of solutes into tissue slices. The experiments demonstrate that the penetration of solutes (such as oxygen or tetrazolium salt) is frequently decreased under experimental conditions common to many metabolic processes and that quantitative measurements which do not take this factor into account could be in considerable error. In addition to illustrating the variables affecting the penetration of solutes, the tetrazolium salt studies demonstrate the usefulness of applying histochemical procedures to metabolic slice studies. An algebraic modification of Warburg's formula has been presented which provides a means of correcting quantitative data obtained on incompletely penetrated slices.