INCREASED PO-2 ALTERS THE BIOELECTRIC PROPERTIES OF FETAL DISTAL LUNGEPITHELIUM

At birth the lung must efficiently clear the liquid from its air space s and permanently convert from a fluid-secreting to a fluid-absorbing organ. When primary cultures of rat fetal distal lung epithelium (FDLE ) grown on permeable supports were switched from a fetal (3%) to a pos tnatal (21%) oxygen environment, there was an increase in epithelial p ermeability as reflected by a dose-dependent decline in transepithelia l resistance (R(t)) 4h later (3% = 239 +/- 19 Omega . cm(2); 21% = 170 +/- 28 Omega . cm(2); 50% = 98 +/- 20 Omega . cm(2); P < 0.05). The e ffect was transient, since monolayers initially maintained at 3% and s witched to these higher oxygen concentrations subsequently had R(t) va lues comparable to the 3% group at 48 h (3% = 153 +/- 17 Omega . cm(2) ; 21% = 181 +/- 19 Omega . cm(2); 50% = 192 +/- 21 Omega . cm(2); P = NS). Changes in Rt were associated with expected changes in the histol ogical appearance of the interepithelial tight junctions, but intracel lular actin content and distribution remained constant. Amiloride-sens itive equivalent short-circuit current increased within 18 h, with fur ther increases after 48 h of exposure to postnatal oxygen concentratio ns. Ion substitution experiments suggested diminished FDLE Cl transpor t and increased Na transport. The amount of FDLE-alpha, -beta, and -ga mma rat epithelial Na channel mRNA increased within 48 h of increasing the ambient oxygen concentration. These results suggest that the phys iological increase in alveolar PO2 at birth is, at least in part, resp onsible for distal lung's permanent switch from Cl secretion to Na abs orption at birth.