Figure 6. Effects of isoprenaline upon ouabain-sensitive I_SC at fetal and neonatal P_O2.

FDLE cells were initially maintained at a P_O2 of 23 or 100 mmHg for 24 h and then either transferred between these two environments or allowed to remain at their original P_O2. Both groups of cells were then cultured for a further 24 h before being mounted in Ussing chambers where ouabain-sensitive I_SC was quantified in both unstimulated cells (□) and cells that had been exposed to isoprenaline for 30–40 min (▪). Experiments were undertaken using a strictly paired experimental protocol in which all measurements were made using cells isolated from the same litters (n = 7). Analysis of variance revealed that the data from unstimulated and isoprenaline-stimulated cells belonged to the same statistical population. We thus conclude that this drug has no effect upon the ouabain-sensitive currents recorded from cells maintained under any of the culture regimes tested. This did show, however, that the different culture regimes used provided a statistically significant source of variability between the data. Student's t test followed by Bonferroni's post hoc correction was therefore used to compare the data obtained from cells that had been exposed to increased P_O2 for all or part of the 48 h culture period with the equivalent data from cells maintained continuously at 23 mmHg. The results of this analysis are indicated by asterisks (***P < 0.02, **P < 0.01, *P < 0.05).