Hydrogen and Potassium Ions Are Interrelated in Acid-Base Homeostasis
Acid-base disturbances affect the distribution of potassium within the body. A decrease in blood pH leads to an increase in the plasma K1 concentration [K+] (hyperkalemia), whereas a blood alkalosis leads to a decrease in plasma ∣ K’ ] (hypokalemia).
The hyperkalemia accompanying blood acidosis is a consequence of reduced activity of the Nat-K+ pump and the Na7K7CΓ co-transporter, both of which normally transport K* back into the cell. In addition, intracellular acidosis liberates K+ from nondifiusible intracellular anions so that more Kt is free to diffuse out of the cell. In the case of blood alkalosis, high [HCO3'] can stimulate K' uptake into cells.Just as changes in blood pH affect [ K1 ], the converse also is true. Hypokalemia is frequently associated with metabolic alkalosis, and hyperkalemia with metabolic acidosis. These changes are a consequence of the actions of K+ on the renal tubule. Depletion of Kt increases H^ elimination by (1) increasing tubular Na+∕H+ exchange and basolateral Na7HCO3^ cotransport; (2) increasing NH3 synthesis and NH4‘ excretion; and (3) stimulating K4/Hr exchange in the collecting tubules. Increases in K' cause metabolic acidosis by inhibition of NH3 synthesis and NH ∣, excretion.