Effect of potassium concentration and ouabain on the renal adaptation to potassium depletion in isolated perfused rat kidney
Authors: Ornt Daniel B. 
Published: April 2011

Renal adaptation for potassium (K) conservation has been demonstrated in isolated perfused kidneys from rats within 3 days of K depletion and appears to be independent of aldosterone and sodium excretion. This study was designed to investigate whether the renal adaptation for K conservation is independent of ambient [K] and renal tissue levels of K and whether ouabain may have effects on K excretion, which are in constrast to the effects on K excretion in normal animals, in the first study, rats K depleted for 3 days received 2500 μequiv. KCl intraperitoneally, while other K-depleted rats and a group of control diet animals received intraperitoneal H2O alone to determine whether simple restoration of K deficits would reverse the renal adaptation for K conservation. Intraperitoneal KCl increased plasma [K] and kidney tissue K significantly within 3 h in the K-repleted group compared with the K-depleted rats. Isolated kidneys were perfused from the three groups of rats 3 h after intraperitoneal injection. Despite K repletion in vivo, perfused kidneys from the K-repleted group still had significantly decreased K excretion (1.28 ± 0.085 μequiv./min) compared with controls (2.05 ± 0.291 μequiv./min), and K excretion was still not different from the K-depleted group (0.57 ± 0.134 μequiv./min). However, fractional K excretion by the kidneys from K-repleted rats was increased above K-depleted kidneys (0.48 ± 0.051 vs. 0.18 ± 0.034, p < 0.01). Despite the increased renal tissue K in K-repleted kidneys at the start of perfusion (285 ± 5.1 vs. 257 ± 5.4 μequiv./g), by the end of the perfusion tissue K in perfused kidneys was identical in all three groups. In the second study, isolated kidneys were perfused from 3-day K-depleted or control rats with either 2 or 6 mM [K] in the perfusate. Isolated kidneys adapted to 3 days of K depletion excreted less K at both 2 and 6 mM [K] compared with controls at the same ambient [K]. The linear relationship of K excretion to perfusate [K] was significantly different in controls compared with low K adapted kidneys (p < 0.001). Finally, when 10−4 M ouabain was added after 60 min of perfusion in kidneys from control diet rats, there was a sodium diuresis and fractional K excretion decreased significantly (0.55 ± 0.043 to 0.32 ± 0.044, p < 0.01). However, in low K adapted kidneys, ouabain had no effect on fractional K excretion (0.020 ± 0.051 to 0.18 ± 0.038) despite a similar increase in sodium excretion. Perfusions of kidneys from 3-day K-depleted rats at 4 × 10−3 M ouabain gave similar results, showing no change in fractional K excretion. Low K adaptation to K depletion developed within 3 days and was not totally abolished by acute K repletion. Maneuvers that favored either a decrease in renal tissue K or an increase in tissue K did not reverse low K adaptation, although renal tissue K levels did alter the rate of K excretion in both controls and K-depleted kidneys. Therefore, a reduction in tissue K was clearly not the sole mediator of renal K conservation. Finally, the markedly different response of low K adapted kidneys to ouabain compared with controls strongly suggests a mechanism for K reabsorption that developed within 3 days of K depletion and is ouabain sensitive.