Potassium excretion: a story that is easy to digest

The aim of this article is to consider how a large quantity of potassium (K+) can be excreted without the development of hyperkalemia. The hypothesis will focus on interactions between K+ and HCO3- primarily within the kidneys. It is speculated that the absorption of K+ from the gastrointestinal tract is accompanied by an initial addition of HCO3- to the body; this in turn could, via intrarenal events, promote the delivery of HCO3- to the cortical collecting duct (CCD), where interactions may permit the development of a very high rate of excretion of K+. To test one portion of this hypothesis, studies were performed in sheep because they normally consume approximately 10-fold more K+ per kilogram body weight than do humans. In the absence of a significant degree of anabolism, there is only a limited potential to shift K+ acutely into cells. Hence, an extremely large capacity to excrete K+ is required to avoid a severe degree of hyperkalemia. The excretion of K+ depends primarily on the ability to have a sustained rise in the (K) in each liter of luminal fluid exiting the CCD to very high levels and to have a large number of liters of fluid exit the terminal CCD while antidiuretic hormone is acting. A reasonable approximation of this CCD flow rate can be obtained by examining the osmole excretion rate when ADH acts. Because these sheep excreted 1,650 mosmol (2 L x 827 mosm/kg H2O) per day, a minimum estimate for volume delivery out of the CCD is 5 to 6 L/day.(ABSTRACT TRUNCATED AT 250 WORDS)