Effects of Angiotensin on Na and K Exchanges in Blood Vessels

Sydney M. Friedman and Constance L, Friedman Department of Anatomy, The University of British Columbia, Vancouver, Canada 

In what follows, we shall show that it is possible to characterize and to distinguish the truly cellular from the paracellular components of both sodium and potassium and, further, to show how these may be related to peripheral vascular resistance. Although our findings are with inulin measurements, essentially similar 

Two basic paracellular components of Na may be distinguished in the phase which inulin does not enter, one temperature-sensitive the other not. These components are mobilized directly upon exposure of the tissue to a medium in which NaCl is replaced by an uncharged substitute such as lactose (Fig, 1), The actual amount mobilized is directly related to the concentration of Na in the medium and more is removed at 37°C than at 2°C in neither case is any associated movement of potassium observed. The duration of exposure is not particularly important since the process is rapid. We classify these components as paracellular since not only are they mobilized within the short time it takes for the new medium to diffuse through the tissue but they are not affected by metabolic inhibitors. These paracellular components are thus probably trapped and bound by the abundant polyelectrolytes of the paracellular matrix. Together, the Na of the free extracellular fluid and of these paracellular components can account for as much as 95% of the total Na in the arterial wall. The remaining amount, which we shall show to be in cells, is of the same order of magnitude as that found in skeletal muscle. 

Na and K content of the inulin-inaccessible phase of rat tail artery following incubation in NaCl-free medium. 

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