Initial effect of sodium bicarbonate on intracellular pH depends on the extracellular nonbicarbonate buffering capacity.

Objective: The effect of sodium bicarbonate on intracellular pH under conditions close to those in vivo, with both bicarbonate and nonbicarbonate buffering systems, is unknown. We postulated that this effect depends on the nonbicarbonate buffering capacity because the alkali-induced back-titration of these buffers results in a concentration-dependent release of CO2 in the extracellular space, leading to a decrease in intracellular pH.

Design: The study was conducted in two stages.