Na+ transport properties of the peritubular membrane of cortical collecting tubule.

The effects of varying endogenous aldosterone levels on the passive and active properties of the peritubular membrane were studied. Rabbits that were fed either a low Na+ (normal K+) diet or a high Na+, low K+ diet increased or decreased plasma aldosterone, respectively. Tubules were dissected, filled with oil, and incubated in 0 K+ medium to increase intracellular sodium. Cellular sodium and potassium content was measured by helium-glow photometry. The degree to which cells accumulate sodium and lose potassium is a function not only of time of exposure but also of diet. Tubules from animals on a low Na+ diet are about 6 times more permeable to sodium than those from animals fed a high Na+ diet. When tubules were loaded with sodium and returned to a normal (5 mM K+) bathing medium, net sodium efflux and potassium influx occurred. The rate of sodium efflux by cortical collecting tubules dissected from animals on the low Na+ diet was 2.3 times greater than the efflux rate of tubules from animals on the high Na+ diet. These data suggest that high levels of endogenous aldosterone enhance sodium transport measured in vitro across the peritubular membrane of cortical collecting tubule.