Radioactive tracer movements across a barrier which can be mounted between two solutions

In general, the experimental procedure is to mount the membrane or the tissue which may be composed of many layers of cells between two compartments as shown in Fig. 1. The two solutions which are homogeneous and of identical composition, are stirred constantly. The labelled substance (THO, or radioactive nonelectrolyte) is 

In the case of the movement of labelled water (THO), the diffusional permeability coefficient, P., in cm/s can be calculated as follows  

Under steady-state conditions, Jj q is constant and Eqn. 1 can be integrated to give 

Ax is the thickness of the pathway, and y the partition coefficient. It is assumed that the concentration in the membrane is related to the concentration in the bulk phase by the partition coefficient y and it is further assumed that the partition coefficient is identical for the two sides of the membrane. Under the usual experimental conditions Cj q tho therefore Pj can be calculated from the experimentally determined /xho tho- The surface area available for diffusion and the volumes of the two compartments must be taken into consideration in calculating 

Basically, identical theoretical analysis as well as experimental procedures are used in the case of studying the movement of small polar nonelectrolytes. 

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