Expression of na' transport and shunt conductance by A6 epithelia: Dependence on substrate of tissue culture inserts

We measured open-circuit voltages (V_oc). short-circuit currents (I_sc). and "resistances" to evaluate expression of Na⁺ transport by mature confluent A6 epithelia grown on a variety of permeabilized supports. Since the cells, growth conditions and all other factors were the same, differences in transport could be attributed alone to the substrate on which the cells were grown. Tissues were grown on both large and small diameter inserts with differing edge length to area ratios (E/A) so that the contribution of the edge conductance to the shunt conductance (edge + tight junction) could be evaluated. Shunt and cellular conductances and the Thévenin ENa were determined after amiloride inhibition of Na transport in control and aldosterone stimulated tissues. Marked differences among substrates were observed not only for the ! of control (0.09 to 3.94 uA/crn:) and aldosterone treated tissues (1.53 to 28.24 uA/cm:), but also the Vc of control (0.6 to 28.6 mV) and aldosterone treated tissues (17.7 to 96.2 mV). Shunt resistance among substrates (large inserts) ranged between 7058 and 38,281 Ocm2, attributable in most inserts entirely to the edge conductance. In some, but not all inserts, aldosterone decreased the junctional conductance. Substrate alone is a major factor in how A6 cells express Na⁺ transport, their tight junctions and aldosterone sensitivity.