Colon epithelial electrical responses to acute hyposia and reoxygenation in vitro

ABSTRACT

Electrogenic epithelial transport depends on oxidative metabolism. Acute hypoxia and subsequent reoxygenation effects on short-circuit current (Isc), transepithelial potential difference (PD) and tissue resistivity (TR) of rat distal colon were assessed. The tissue was mounted in an Ussing chamber filled with Ringer-HCO3 -solution at 37 degrees Celsius and bubbled with 95 per cent O2- 5 per cent CO2 which was switched to 95 per cent N2- 5 per cent CO2 for inducing hypoxia; afterwards normal oxygenation was resumed. The effect of 5, 10, 15 and 20 min-hypoxic periods was assessed in isolataed mucosa preparations. Recovery was complete after 10- and 15-min hypoxia, but not after 20-min hypoxia. After 5-min hypoxia, an overshoot of Isc and PD was seen on reoxygenation. This effect was further characterized comparatively in mucosa-submucosa and isolated mucosa preparations. In the former (n=10), control values were Isc= 71,7 + 8,6 muA,. cm-2, PD = 9,7 + 1,6 mV and TR = 134,9 + 13,6 (. cm2. A 5-min hypoxia reduced Isc by 47.2 + 7,3 per cen+t and PD by 61,5 + 4,9 per cent. Peak values on reoxygenation were 28,1 + 4,1 per cent for Isc and 16,8 + 5,4 per cent for PD, over controls values. In the osilated mucosa (n=9), control values were Isc= 52,04 + 5,5 muA. cm-2, PD = 5,0 + 0,8 mV and TR = 101,04 + 10,5 (. cm2. In hypoxia, Isc decreased by 64,5 + 7,6 per cent and PD by 57,2 + 7,8 per cent. On reoxygenation peak values of 78,0 + 19,0 per cent and 87,5 + 17,1 per cent, respectively, were seen. The response to a 5 min-hypoxia was comparable, but that to reoxygenation was weaker and slower, in mucosa-submucosa than in isolated mucosa preparations. This may be explained by a hindrance to oxygen diffusion caused by the submucosal tissue. TR did not change with any period of hypoxia tested, but decreased slightly (8,9 + 1,3 per cent) upon reoxygenation in the mucosa-submucosa preparations. Ouabain (10(-3)M) markedly blunted the response to reoxygenation. We conclude that hypoxic periods of 20 min lead to irreversible functional deterioration. Hypoxia decreases electrogenic transepithelial pumping, which may allow sodium to accumulate intracellularly and, if the hypoxia is short enough to prevent damage to the epithelium, increase sodium pump activity when oxygenation is resumed.