Asymmetrical oxygen availability from serosal and luminal sides of rat distal colon epithelium.

ABSTRACT

Short-circuit current (Isc) and transepithelial potential difference (PD) of the rat distal colon mucosa are sensitive to acute hypoxia in vitro. The relative contribution of luminal and serosal oxygenation in sustaining Isc and PD was assessed. Rat distal colon Isc and PD responses to hypoxia and reoxygenation of preparations of mucosa-submucosa, and of isolated mucosa (with and without the mucus gel layer), mounted in an Ussing chamber, and of sacs of everted and non-everted isolated mucosa, were measured. In Ussing chambers, a 5-min total (bilateral) hypoxia reduces Isc and PD by 50 to 70%, while an overshoot was observed on reoxygenation. Serosal hypoxia caused about the same effect as total hypoxia, with complete recovery on reoxygenation. Luminal hypoxia had no effect in either Isc or PD. After total hypoxia, selective serosal reoxygenation allowed complete recovery of Isc and PD; addition of luminal reoxygenation did not further increase Isc and PD. Luminal reoxygenation after total hypoxia did not modify the decrease in Isc and PD, but addition of serosal reoxygenation led to complete recovery. A similar behaviour was seen in isolated mucosa preparations without the mucus gel layer. Baseline Isc and PD of everted sacs were about 45% of those of non-everted sacs, but their response to a hypoxic challenge was slightly attenuated. On reoxygenation, both everted and non-everted sacs showed complete recovery. Summing up serosal oxygenation is both necessary and sufficient to sustain rat distal colon Isc and PD, while luminal oxygenation is not; there seems to exist a barrier, different from the mucus gel layer, for oxygen access from the luminal side of the epithelium; and distal colon isolated mucosa everted sac preparations are suboptimally oxygenated.