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The effects of P_O2 upon transepithelial ion transport in fetal rat distal lung epithelial cells

S. J. Ramminger, D. L. Baines, R. E. Olver and S. M. Wilson

1. Isolated rat fetal distal lung epithelial (FDLE) cells were cultured (for 48 h) at P_O2 levels between 23 and 142 mmHg. Higher P_O2 levels between 23 and 142 mmHg. Higher P_O2 was associated with increased short circuit current (I_SC) and increased abundance of the Na⁺ channel protein -ENaC. P_O2 had no effect upon I_SC remaining after apical application of amiloride (10 µM).

2. Studies of cells maintained (for 48 h) at P_O2 levels of 23 mmHg or 100 mmHg, and subsequently nystatin permeabilized (50 µM), showed that high P_O2 increased Na⁺ pump capacity. This response was apparent 24 h after P_O2 was raised whilst it took 48 h for the rise in I_SC seen in intact cells to become fully established. Both parameters were unaffected by raising P_O2 for only 30 min.

3. Basolateral application of isoprenaline (10 µM) did not affect I_SC in cells maintained at 23 mmHg but evoked progressively larger responses at higher P_O2. The response seen at 142 mmHg was larger than at 100 mmHg, the normal physiological alveolar P_O2.

4. Isoprenaline had no effect on Na⁺ pump capacity at P_O2 levels of 23 mmHg or 100 mmHg, but stimulated Na⁺ extrusion at 142 mmHg. Increasing P_O2 above normal physiological levels thus allows the Na⁺ pump to be controlled by isoprenaline. This may explain the enhanced sensitivity to isoprenaline seen under these slightly hyperoxic conditions.

5. Changes in P_O2 mimicking those occurring at birth thus exert profound influence over Na⁺ transport in FDLE cells and the Na⁺ pump could be an important locus at which this control is exercised.

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