Electrical conductivity and its use in estimating an equivalent pore size for arterial endothelium

Transport characteristics of capillary endothelia have been studied in numerous preparations. Little is known, however, regarding transport across the ultrastructurally similar arterial endothelium. The present studies describe a method for determining endothelial electrical resistance in the isolated, Ringer-perfused rabbit aorta. By use of silver-silver chloride electrodes, total resistance (RT) of the vessel wall was found to be 18.4 +/- 6.5 omega . cm2 (mean +/- SD; n = 10) in response to transmural passage of constant current pulses. After detergent removal of the endothelium, outer layer resistance (Rol) was 8.7 +/- 5.1 omega . cm2. Endothelial resistance (Re) was calculated to be 9.7 +/- 4.1 omega . cm2, since RT = Rol + Re. Combination of Re with previously measured hydraulic conductivity of this endothelium yielded an equivalent endothelial pore radius of 85 A, whereas a fractional pore area of 6.5 X 10(-4) was estimated from conductivity data. An alternative analysis demonstrated an endothelial slit width of 102 A. Re is similar to electrical resistances of leaky epithelia, frog mesenteric capillary, and frog muscle capillary, suggesting similar permeability characteristics in both arterial and capillary endothelia.