Oxygen‐evoked Na+transport in rat fetal distal lung epithelial cells

1Monolayer cultures of rat fetal distal lung epithelial (FDLE) cells generated larger spontaneous short circuit currents (ISC) when maintained (48 h) at neonatal alveolar PO2(100 mmHg) than at fetal PO2(23 mmHg). When cells were shifted between these atmospheres in order to impose a rise in PO2equivalent to that seen at birth, no rise in ISCwas seen after 6 h but the response was fully established by 24 h.2Studies of basolaterally permeabilised cells revealed a small rise in apical Na+conductance (GNa) 6 h after PO2was raised but no further change had occurred by 24 h. A substantial rise was, however, seen after 48 h.3Reporter gene assays showed that no activation of the α‐ENaC (epithelial Na+channel α‐subunit) promoter was discernible 24 h after PO2was raised but increased transcriptional activity was seen at 48 h.4Studies of apically permeabilised cells showed that a small rise in Na+pump capacity was evident 6 h after PO2was raised and, in common with the rise in ISC, this effect was fully established by 24 h. The rise in ISCthus develops 6‐24 h after PO2is raised and is due, primarily, to increased Na+pump capacity.5The increase in GNathus coincides with activation of the α‐ENaC promoter but these effects occur after the rise in ISCis fully established and so cannot underlie this physiological response. The increased transcription may be an adaptation to increased Na+transport and not its cause.