Short chain fatty acids and potassium uptake in a simple lipid-water partition.

Chemical evidence is presented to demonstrate that short chain fatty acids selectively bind potassium instead of sodium in a simple lipid-water partition. The preference for potassium ions as measured by the K+/Na+ relationship increases from valeric acid (C5) to the higher members of the series, reaching a maximum at pelargonic acid (C9) under physiological conditions (37 C and potassium and sodium concentrations as in normal serum). Anions play a very important role in the selection of K+ ions. When NaHCO3, at the concentration present in normal serum, is added to the aqueous phase, a great increase in the absorption of K+ ions is observed, if compared with the same solution without NaHCO3 and at the same pH. A model is described as a working hypothesis which would explain the behavior of the fatty acids.