Response of yeast pH to weak acid treatment.

<p>(<b>A</b>) pH response of BCECF-AM loaded yeast cells (red) compared with pHlash transformed yeast cells (blue). (<b>B</b>) Response of BCECF-AM loaded yeast cells to weak acid (20 µM sodium butyrate, upper panel). Yeast cells were suspended in 20 mM MES buffer (pH 5.0). After 10 min baseline recording, 20 µM final concentration of Na-butyrate (pH 5.0) was added (total added volume was 20 µl, which is the same volume as that for the pH 5.0 buffer that was used as a control in the lower panel). (<b>C</b>) Response of pHlash-expressing yeast cells to weak acid. Yeast cells were suspended in 20 mM MES buffer (pH 5.0) with 10 µM native coelenterazine. After 10 min baseline recording, 20 µM final concentration of Na-butyrate (pH 5.0) was added (upper panel). An equal volume of pH 5.0 buffer was added as control (lower panel). The change in BRET ratio of pHlash reports the intracellular acidification after treatment with Na-butyrate. (<b>D</b>) Histogram depiction of multiple replicates of the BCECF protocol illustrated in panel B. (<b>E</b>) Histogram depiction of multiple replicates of the pHlash protocol illustrated in panel C. In panels A, D, and E, error bars are +/− S.D., but in some cases the error bars are so small that they are obscured by the symbols (n = 3 for panel A, n = 5 for panels D and E). ** p<0.01.