Ion exchange properties of the canine carotid artery.

Properties of the ion exchange mechanisms in the arterial wall were investigated by comparing water and electrolyte contents, and by measuring the steady-state entry of (22)Na, (42)K, and (26)Cl under similar in vitro conditions. Overnight incubation of freshly dissected slices at 2 degrees C resulted in an accumulation of sodium, chloride, and water and a loss of potassium. Subsequent incubation at 37 degrees C in a physiological solution resulted in a reversal of these processes. Loss of water, sodium, and chloride at 37 degrees C could also take place into a potassium-free solution. Under all conditions studied the quantity of fast exchanging electrolyte (half time less than 3 min) exceeded that contained in the inulin and sucrose spaces. The excess could not be attributed to connective tissue adsorption. A kinetic model was applied to the flux data which incorporated two simultaneous processes: bulk diffusion and a reversible reaction. The assumption that the cell membrane behaved as a discrete barrier for the exchange of all cell electrolyte was relaxed in this approach. A theory based upon the physicochemical properties of proteins, ions, and water in biological systems provided a physical basis for the kinetic model, and for interpreting the ion exchange properties of the vascular wall.