Ion fluxes and electrical characteristics of the short-circuited rat colon in vitro.

The unidirectional fluxes of sodium and chloride across stripped rat colon mucosa were measured and compared with the electrical characteristics of the tissue under voltage-clamped conditions. The relationship between the serosal-mucosal fluxes of the two ions and an imposed potential revealed that the serosal-mucosal flux of sodium was entirely paracellular, whereas there was also a transcellular component of the corresponding chloride flux. In the absence of sodium, the short-circuit current and net chloride flux were abolished; in the absence of chloride, the net sodium flux was reduced but not abolished, and the short-circuit current was unchanged. From an analysis of the effects of the inhibitors, amiloride, theophylline, acetazolamide, furosemide and piretanide, a plausible model was developed to explain the characteristics of these transports. It was proposed that both membranes possess Cl-/HCO-3 antiports, though their sensitivities to inhibitors were different. There is also a Na+/Cl- symport and an electrogenic sodium entry mechanism in the brushborder membrane.