title: The contributions of respiration and glycolysis to extracellular acid production.
abstract: BACKGROUND
  The rate at which cells acidify the extracellular medium is frequently used to report glycolytic rate, with the implicit assumption that conversion of uncharged glucose or glycogen to lactate(-)+H(+) is the only significant source of acidification. However, another potential source of extracellular protons is the production of CO2 during substrate oxidation: CO2 is hydrated to H2CO3, which then dissociates to HCO3(-)+H(+).
  
  
  METHODS
  O2 consumption and pH were monitored in a popular platform for measuring extracellular acidification (the Seahorse XF Analyzer).
  
  
  RESULTS
  We found that CO2 produced during respiration caused almost stoichiometric release of H(+) into the medium. With C2C12 myoblasts given glucose, respiration-derived CO2 contributed 34% of the total extracellular acidification. When glucose was omitted or replaced by palmitate or pyruvate, this value was 67-100%. Analysis of primary cells, cancer cell lines, stem cell lines, and isolated synaptosomes revealed contributions of CO2-produced acidification that were usually substantial, ranging from 3% to 100% of the total acidification rate.
  
  
  CONCLUSIONS
  Measurement of glycolytic rate using extracellular acidification requires differentiation between respiratory and glycolytic acid production.
  
  
  CONCLUSIONS
  The data presented here demonstrate the importance of this correction when extracellular acidification is used for quantitative measurement of glycolytic flux to lactate. We describe a simple way to correct the measured extracellular acidification rate for respiratory acid production, using simultaneous measurement of oxygen consumption rate.
  
  
  CONCLUSIONS
  Extracellular acidification is often assumed to result solely from glycolytic lactate production, but respiratory CO2 also contributes. We demonstrate that extracellular acidification by myoblasts given glucose is 66% glycolytic and 34% respiratory and describe a method to differentiate these sources.
authors.affiliation: College of Pharmacy, Touro University California, 1310 Club Drive, Vallejo, CA 94592, USA; Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, USA. Electronic address: shona.mookerjee@tu.edu.
authors.forename: Shona A
authors.initials: SA
authors.lastname: Mookerjee
authors.affiliation: Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, USA.
authors.forename: Renata L S
authors.initials: RLS
authors.lastname: Goncalves
authors.affiliation: College of Pharmacy, Touro University California, 1310 Club Drive, Vallejo, CA 94592, USA; Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, USA.
authors.forename: Akos A
authors.initials: AA
authors.lastname: Gerencser
authors.affiliation: Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Nicholls
authors.affiliation: College of Pharmacy, Touro University California, 1310 Club Drive, Vallejo, CA 94592, USA; Buck Institute for Research on Aging, 8001 Redwood Blvd, Novato, CA 94945, USA.
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002478:Cells, Cultured; D006019:Glycolysis; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism; D051379:Mice; D010101:Oxygen Consumption; D051381:Rats
chemical_list: D002245:Carbon Dioxide; D019344:Lactic Acid
keywords: Bicarbonate; Carbon dioxide; Extracellular acidification rate; Extracellular flux; Glycolysis; Oxygen consumption rate