(A) Src kinase activity in fibroblasts derived from mice deficient in src (src⁻) or csk (csk⁻). The results are expressed as the ratio of activity to that wild-type fibroblast cells (src wt) and are the means ± SE of 6 independent experiments. As would be anticipated, the cells deficient in src had negligible src kinase activity, while those deficient in the regulatory csk had significantly increased activity. (*P < .05). (B) RNase protection analysis of gene expression. The cells were exposed in parallel to varying oxygen concentrations for 4 hours (21%, 1%, 0.1%, and anoxia). Results are expressed as the ratio of the mRNA of interest to that of the actin control (×100) and are the means ± SE of 5 independent experiments. Despite the substantial differences in src kinase activity between the cells, no significant differences were seen in the expression of VEGF or Glut-1 at any oxygen tension.