Concentration-dependence of dithiothreitol effects on rat distal colon electrophysiology

Dithiothreitol (DTT), at 1 mmol/L or higher, is widely used as a mucolytic in gastrointestinal research. Previous observations suggest that it may be toxic to the mucosa. DTT effects on the mucosal electrical behavior were assessed. Cumulative concentration-response relationships of DTT effects on rat distal colon mucosa were studied. Isolated mucosa preparations were mounted in an Ussing chamber under short-circuit conditions. The effects of concentrations ranging from 1 mumol/L to 1 mmol/L, applied to either the mucosal or serosal side, were studied. As compared with control, untreated preparations, DTT depressed short-circuit current at 10 mumol/L and higher when applied to the serosal side, and at 50 mumol/L and higher when applied to the mucosal side of the epithelium. On the other hand, transepithelial resistivity showed a progressive increase with DTT applied to either side at a concentration of up to 500 mumol/L, while at the highest concentration (1 mmol/L) a marked decrease in resistivity occurred. Neither the short-circuit current decrease, nor the resistivity collapse showed recovery after repeated rinsing with DTT-free solution. It is concluded that DTT affects epithelial electrical properties at low concentrations, and therefore its use as a mucolytic for electrophysiological studies should be discouraged.