Cancer cells require extracellular acidic pH to maintain high levels of ATP.

To MDA-MB-231 cell suspensions in PBS-10% FBS containing 10 μM oligomycin was added 0.1% glucose under gentle mechanical stirring. The pH of the medium (extracellular pH) was monitored in real time while ATP, glucose and lactate were measured (per million cells) from aliquots taken out at indicated time points (error bars = 2.s.d., n = 3). (A) Steady state ATP and acid extrusion (pH) during glycolysis. The ATP values increased continuously relative to the starting value with gradual decrease in the pH of the external medium. (B) Glucose consumed (open circle) and lactate produced (solid circle) with time for the experiment in panel A. (C) Steady state ATP upon continuous neutralization of acid. The secreted acid was continuously neutralized by adding small aliquots of alkali. The ATP values remained almost unchanged relative to the starting value under this condition. (D) Glucose consumed (open circle) and lactate produced (solid circle) for the experiment in panel C. These experiments were repeated three times.