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

Abstract

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 serosalmucosal 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 shortcircuit 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 posses 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.