(A) Src kinase activity in Hep3B cells stably transfected with plasmids encoding src, a kinase inactive mutant src, or csk. The stably transfected cells were assayed for src kinase activity in parallel with control cells transfected with the neomycin resistance plasmid alone (neo). Cells were exposed to hypoxia (1%) or normoxia for 60 minutes. The results are expressed as the ratio of activity to that of the normoxic control and are the means ± SE of 3 independent experiments. Alterations in src kinase activity consistent with the overexpression of the src gene, src-dominant negative gene, and the csk gene were seen. Significant differences in src kinase activity from normoxic control transfectants (neo) are indicated (*P < .05). Exposure of cells to 1% oxygen produced no significant changes in src kinase activity in any of the transfectants. (B) RNase protection analysis of expression of genes induced by hypoxia in the Hep3B stable transfectants. The cells were exposed in parallel to 21% oxygen or 1% oxygen for 4 hours. The results are expressed as the ratio of the mRNA of interest to that of the actin control (×100) and are the means ± SE of 3 independent experiments. Despite the substantial alterations in src kinase activity, no significant differences were seen in the normoxic expression or hypoxic induction of any gene.