Figure 5.

Bicarbonate increases total phosphorylation in A431 cells after EGF ligand stimulation. A, A431 cells were grown and incubated overnight in low-serum HEPES-buffered (50 mm) DMEM at pH 7.4 with 0, 40, and 60 mm bicarbonate added and equilibrated with 0, 5, and 10% CO₂, respectively, as indicated. The cells were then stimulated with EGF and analyzed for total phosphotyrosine. B, densitometry for three independent experiments, of short- and long-exposed membranes, for high-molecular weight (HMW) phosphorylated proteins, and ∼28 kDa band, respectively (dashed rectangles in A) quantified in relation to Ponceau staining with 2-, 4-, and 6-min time points combined (n = 3; mean ± S.D. (error bars); *, p < 0.05). Symbols indicate individual results. IB, immunoblotting.