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

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Abstract
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 Na. Cellular Na and K content was measured by He-glow photometry. The degree to which cells accumulate Na and lose K is a function not only of time of exposure but also of diet. Tubules from animals in a low Na+ diet are about 6 times more permeable to Na than those from animals fed a high Na+ diet. When tubules were loaded with Na and returned to a normal (5 mM K+) bathing medium, net Na efflux and K 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 in the high Na+ diet. Apparently, high levels of endogenous aldosterone enhance Na transport measured in vitro across the peritubular membrane of cortical collecting tubule.