Role of Renal Tubular Secretion in Potassium Homeostasis

Abstract

The changes in Na and K excretion which accompanied induced changes in Cl excretion were studied in K-depleted and K-fed dogs. Diuretic agents and infusions of isotonic sodium chloride solution were used to vary Cl excretion both when the animals were normally hydrated and during water diuresis. In all cases, it was found that changes in Na excretion were accompanied by quite regular and predictable changes in K excretion. In K-depleted dogs, the ratio of the increment in Na excretion to that of K excretion approximated the ratio of the two ions in the glomerular filtrate. This relationship suggests that the renal tubule, in reabsorbing Na and K in conjunction with anions, makes no distinction between the two cations. Thus the renal control of potassium homeostasis depends largely on the tubular secretion of the ion. In dogs in which the stimulus for distal tubular secretion of K had been maintained by a K-rich diet, the increments in K excretion as Na excretion was increased were observed to be much larger than in the K-depleted dogs. It is concluded that this finding demonstrates a partial dependence of distal K secretion upon the availability of the lumenal component of the Na-K exchange mechanism.