title: Influences of acidic conditions on formazan assay: a cautionary note.
abstract: Formazan assay has been used for several decades to evaluate metabolic activity of eukaryotic and prokaryotic cells. In particular, it has been often applied for quantitative assessment of viable cells under acidic circumstances caused by, e.g., ischemia and hypoxia. However, little attention has been paid to the influence of acidic pH on formazan assays. We found that acidic culture conditions significantly affect outcomes of the assays. Absorbance of tetrazolium-formazan decreased in a pH-dependent manner without affecting cell viability. This nonspecific effect was ascribed to influences of acidic pH on the production of formazan. Replacement of culture media to fresh medium at physiologic pH partially overcame this problem. The influence of acidic culture conditions should be carefully considered when formazan assays are used for the assessment of viable cells under various experimental situations.
authors.affiliation: Department of Molecular Signaling, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Shimokato 1110, Chuo, Yamanashi, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Johno
authors.forename: Shuhei
authors.initials: S
authors.lastname: Takahashi
authors.forename: Masanori
authors.initials: M
authors.lastname: Kitamura
mesh_terms: D000143:Acids / Q000032:analysis; D000818:Animals; D002460:Cell Line; D002477:Cells / Q000737:chemistry / Q000378:metabolism; D005562:Formazans / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051381:Rats
chemical_list: D000143:Acids; D005562:Formazans