Figure 1. O₂-evoked changes in I_SC and in transcriptional activity of the α-ENaC promoter.

Experiments were undertaken using cells that were maintained continually at either fetal (a) or neonatal alveolar P_O2 (b), or were transferred between these environments in order to impose a rise in P_O2 equivalent to that seen at birth (c). This shift in P_O2 was imposed 24 h (ic) or 48 h (iic) before the cells were used in experiments. The cells were thus maintained in culture for a total of 96 h (i) or 120 h (ii), the prolonged culture period being needed to allow the cells to be transfected with the reporter constructs. A, the total I_SC generated by cells maintained under each of the three regimes (n = 5 for each). B, transcriptional activity of the α-ENaC promoter was determined for cells maintained under each regime (n = 5 for each). Luciferase production by cells transfected with p GLE2.2, which contains the α-ENaC promoter region, was determined and is presented as a fraction of the luciferase formation determined in cells derived from the same litters that had been transfected with the promoterless p GLE.basic construct but otherwise treated identically. Asterisks denote values that differed significantly from the appropriate data (ia and iia) derived from cells maintained continually at fetal P_O2 (*P < 0.05, ***P < 0.01).